Barry’s Introduction to Construction of Buildings 1118977165, 9781118977163

Table of contents :
Title Page......Page 5
Copyright Page......Page 6
Contents......Page 7
Preface......Page 11
How to Navigate this Book......Page 13
1.1 The construction process......Page 15
Function......Page 16
Performance......Page 17
Economics......Page 18
1.3 Building: the (de-carbonised) product
......Page 19
1.4 Responding to climate change......Page 20
Energy efficiency and environmental performance......Page 21
Loadbearing or framed construction?......Page 22
Design and constructability......Page 23
Prefabrication and offsite production......Page 24
Building control and building regulations......Page 25
1.7 Making choices and sources of information......Page 26
A note of caution......Page 27
2.1 Site analysis......Page 31
The ‘desktop’ study......Page 32
Site reconnaissance and surveys......Page 35
Soil investigations......Page 38
Exploratory investigation and foundation systems......Page 41
Ground and soil tests......Page 43
2.2 Site set-up and security
......Page 44
Security and safety......Page 45
Temporary weather protection......Page 46
Site preparation......Page 47
Sustainable drainage system (SuDS)......Page 48
Surface water drainage......Page 49
Laying drains......Page 54
Drainage layout......Page 55
Drainpipes......Page 56
Drain laying......Page 62
Access points to drains......Page 70
Drain testing......Page 78
Sewage collection and treatment......Page 80
Scaffold components......Page 82
Scaffold types......Page 84
Lateral stability – tying into the building......Page 90
Weather protection – scaffold sheetings......Page 92
Independent scaffold systems......Page 93
Edge protection and scaffolding for roofs......Page 95
Trussed-out and suspended scaffolds
......Page 98
Alternative methods of access from heights......Page 102
Rocks......Page 107
Soils......Page 110
Characteristics of soils......Page 112
Volume change......Page 114
Ground instability......Page 115
Bearing capacity......Page 118
Foundation design and subsoil examination......Page 119
Differential settlement (relative settlement)......Page 125
Reusing existing foundations......Page 129
Concrete......Page 130
Foundations on sloping sites......Page 133
Support for foundation trenches......Page 135
Thermally insulated foundations......Page 138
3.5 Strip foundations......Page 140
Stepping strip foundations......Page 141
Wide strip foundation......Page 144
Narrow strip (trench fill or deep strip) foundation......Page 146
Deep strip foundation or mass fill foundations......Page 148
Width of foundations......Page 149
3.6 Pad foundations......Page 151
Combined foundations......Page 155
Gabion pad foundations......Page 158
3.7 Raft foundations......Page 159
Solid slab raft foundation......Page 161
Beam and slab raft foundation......Page 163
Cellular raft foundation (also called ‘buoyant raft’)......Page 165
3.8 Short-bored pile foundations
......Page 167
3.9 Precast pile and beam foundation systems......Page 169
Strength......Page 173
Resistance to the passage of sound......Page 174
Hardcore......Page 176
Damp-proof membrane (DPM)......Page 177
Materials used as DPM......Page 180
Thermal insulation to solid floors......Page 182
Floor surface......Page 184
Floor screeds......Page 185
4.4 Suspended timber ground floors......Page 190
Timber ground floor components......Page 191
Precast ‘T’-beam and infill block floor
......Page 193
Reinforced concrete and clay block floor......Page 194
Monolithic reinforced concrete floor......Page 195
Functional requirements specific to concrete floors......Page 197
Floor joists......Page 198
Functional requirements specific to timber upper floors......Page 201
Jointless floor finishes......Page 207
Floor tiles......Page 209
Concrete tiles......Page 211
Timber floor finishes......Page 212
5.1 Functional requirements......Page 219
Strength and stability......Page 220
Durability and freedom from maintenance......Page 224
Security......Page 225
Stone......Page 226
Bricks and brickwork......Page 227
Blockwork......Page 235
5.3 Mortar......Page 237
Types of mortar......Page 238
5.4 Bonding bricks and blocks......Page 241
Types of bond......Page 242
Bonding blocks......Page 246
5.5 Damp-proof courses (DPCs)
......Page 247
Flexible DPCs......Page 248
Rigid DPCs......Page 252
DPCs in cavity walls......Page 253
5.6 Solid wall construction......Page 255
Rendering......Page 256
Types of render......Page 257
Slate and tile hanging......Page 258
Thermal insulation to solid walls......Page 260
Openings in solid walls......Page 263
Reinforced concrete lintels......Page 266
Pressed steel lintels......Page 269
Brick lintels......Page 270
Brick arches......Page 271
Types of stone walling......Page 276
Openings to stone walls......Page 281
5.7 Cavity wall construction......Page 284
Strength and stability......Page 285
Openings in walls......Page 292
Head of openings in cavity walls......Page 296
Cavity wall insulation......Page 300
Achieving low U-values......Page 307
Preventing heat loss, flanking sound and ensuring fire integrity across party walls formed with a cavity......Page 308
Party walls......Page 312
Straw bale construction......Page 313
Mortar bale......Page 318
5.10 Earth wall construction......Page 319
Earth-sheltered construction
......Page 320
Materials......Page 322
Strength and stability......Page 327
Resistance to weather......Page 328
Resistance to the passage of heat......Page 329
6.2 Pitched roofs......Page 331
Roof types......Page 332
6.3 Pitched roof coverings......Page 352
Plain tiles......Page 353
Interlocking single-lap tiles
......Page 359
Slates......Page 364
Standing seams......Page 370
Felt underlay......Page 371
Cold roof......Page 373
Warm roof......Page 375
Uncontrolled ventilation......Page 377
Thermal bypass at the eaves in warm roofs......Page 378
6.6 Flat roofs......Page 379
Sheet metal covering to timber flat roofs......Page 381
Waterproof membranes for timber flat roofs......Page 389
Laying built-up bitumen felt roofing
......Page 392
Inverted or upside-down roof
......Page 395
Roof coverings......Page 398
Position of the insulation......Page 401
Avoiding thermal bridges......Page 403
Ventilation......Page 405
Weather protection......Page 406
6.11 Green roofs......Page 410
Typical construction......Page 411
6.12 Roof drainage......Page 414
Drainage to pitched roofs......Page 415
Drainage to flat roofs......Page 420
Daylight......Page 425
Quality of daylight......Page 431
Sunlight......Page 433
Strength, stability and airtightness......Page 434
Ventilation......Page 439
Resistance to the passage of heat......Page 442
Resistance to the passage of sound......Page 443
Safety requirements......Page 448
7.2 Window types......Page 450
Hinged opening lights......Page 452
Pivoted opening lights......Page 455
Sliding windows......Page 457
Composite action windows......Page 458
Timber casement windows......Page 460
Steel casement windows......Page 468
Aluminium casement windows......Page 471
Sealants......Page 474
uPVC casement windows......Page 476
Pivoted windows......Page 478
Sliding windows......Page 480
Annealed flat glasses......Page 487
Processed flat glasses......Page 489
Glazing......Page 490
Double and triple glazing......Page 493
Hardware for timber windows......Page 502
7.6 Window cills......Page 503
External cills......Page 504
Internal cills......Page 508
Safe means of access and egress......Page 513
Doors and design considerations (Approved Document M)......Page 514
Privacy......Page 515
Fire safety......Page 516
Airtightness......Page 517
8.2 Door types......Page 518
Panelled doors......Page 521
Glazed doors......Page 531
Flush doors......Page 533
Fire doors......Page 534
Matchboarded doors......Page 538
8.3 Door frames and linings......Page 539
Timber door frame......Page 541
Metal door frames......Page 549
Aluminium doors......Page 550
uPVC doors......Page 551
Garage doors......Page 553
8.4 Hardware......Page 554
Hinges......Page 555
Latches and locks......Page 557
Entry-control systems
......Page 560
Definitions......Page 563
Ease of use......Page 565
Impact sound......Page 566
9.2 Materials, terms and definitions......Page 567
Terms and definitions......Page 568
Stairs with parallel treads......Page 576
9.4 Timber staircases......Page 577
Timber stair construction......Page 578
Open-riser or ladder stair
......Page 586
9.5 Stone stairs......Page 588
Concrete stair construction......Page 590
9.7 Structural glass stairs......Page 594
Internal ramps......Page 595
External ramps providing access to a building......Page 596
External finishes......Page 601
Types of finish......Page 602
Internal plastering......Page 603
Materials used in plaster......Page 606
Background surfaces for plaster......Page 610
Plaster finishes to timber joists and studs......Page 611
Gypsum plasterboard......Page 613
Skirting......Page 618
Architrave......Page 621
10.4 Tiling to walls......Page 622
Colour......Page 623
Paint systems......Page 624
Application of paint......Page 626
Special paints......Page 627
Oils and waxes for timber......Page 628
Wallpaper......Page 629
Resistance to the passage of heat......Page 633
Ventilation......Page 634
Fabric heat loss......Page 635
Calculating U-values
......Page 636
Ventilation heat loss......Page 640
Calculation of total heat loss from a building......Page 641
Heat loss: theory and practice......Page 642
11.3 Indoor climate control......Page 646
Comfort......Page 647
Heating......Page 648
Cooling......Page 649
11.4 Energy sources......Page 650
Renewable sources......Page 652
Open fire......Page 655
Fire safety......Page 657
Flues......Page 660
Chimneys......Page 661
Weathering around chimneys......Page 668
11.6 Domestic gas installations......Page 671
Gas supply......Page 672
Pipework......Page 673
Flues to gas-burning appliances
......Page 674
Electrical distribution......Page 676
Cables and conduits......Page 689
11.8 Artificial lighting......Page 694
Energy-efficient lighting
......Page 695
Lighting outlets......Page 696
11.9 Testing and monitoring thermal performance......Page 697
Inspections during construction......Page 698
Heat flow through building elements......Page 699
Airtightness testing......Page 700
In-use monitoring and building user surveys
......Page 701
Cold water supply......Page 705
Connections to the water mains......Page 706
Cold water supply systems......Page 707
Mains pressure cold water supply......Page 712
Recycled water systems......Page 713
12.2 Hot water supply and distribution......Page 714
Central hot water supply......Page 715
Instantaneous water heaters......Page 716
Mains pressure hot water supply......Page 717
Cistern feed hot water supply......Page 719
Mains pressure supply......Page 722
Gravity feed cold water supply......Page 725
Drinking water storage cistern......Page 727
Low-level cistern
......Page 728
Zoned supply system......Page 729
Copper pipe (copper tubular)......Page 731
Plastic pipe or tube......Page 733
Valves and taps......Page 734
12.5 Sanitary appliances......Page 735
Soil appliances......Page 736
Wastewater appliances......Page 742
Sanitary pipework......Page 746
Soundness test......Page 752
Index......Page 757
EULA......Page 767

Citation preview

BARRY’S INTRODUCTION TO CONSTRUCTION OF BUILDINGS

BARRY’S INTRODUCTION TO CONSTRUCTION OF BUILDINGS Fourth Edition Stephen Emmitt University of Bath UK

This edition first published 2019 © 2019 John Wiley & Sons Ltd Edition History Blackwell Publishing (1e, 2005), Wiley Blackwell (2e, 2010), Wiley Blackwell (3e, 2014) All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions. The right of Stephen Emmitt to be identified as the author of this work has been asserted in accordance with law. Registered Offices John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK Editorial Office 9600 Garsington Road, Oxford, OX4 2DQ, UK For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com. Wiley also publishes its books in a variety of electronic formats and by print‐on‐demand. Some content that appears in standard print versions of this book may not be available in other formats. Limit of Liability/Disclaimer of Warranty While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials or promotional statements for this work. The fact that an organisation, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organisation, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. Library of Congress Cataloging‐in‐Publication Data Names: Emmitt, Stephen, author. Title: Barry’s introduction to construction of buildings / Stephen Emmitt, University of Bath, UK. Other titles: Introduction to construction of buildings | Introduction to the construction of buildings Description: 4th edition. | Hoboken, NJ, USA : Wiley Blackwell, [2019] | Includes bibliographical references and index. | Identifiers: LCCN 2018016658 (print) | LCCN 2018017627 (ebook) | ISBN 9781118977200 (Adobe PDF) | ISBN 9781118977217 (ePub) | ISBN 9781118977163 (pbk.) Subjects: LCSH: Building. Classification: LCC TH146 (ebook) | LCC TH146 .E47 2019 (print) | DDC 690–dc23 LC record available at https://lccn.loc.gov/2018016658 Cover Design: Wiley Cover Image: © sayhmog/iStockphoto Set in 10/12pt Minion by SPi Global, Pondicherry, India 10 9 8 7 6 5 4 3 2 1

Contents

Preface How to Navigate this Book

ix xi

1 Introduction

1

1.1 The construction process 1.2 The function and performance of buildings 1.3 Building: the (de‐carbonised) product 1.4 Responding to climate change 1.5 General principles of construction 1.6 Regulations and approvals 1.7 Making choices and sources of information Chapter 2 AT A GLANCE 2 Site Analysis, Set‐Up, Drainage and Scaffolding 2.1 Site analysis 2.2 Site set‐up and security 2.3 Site drainage 2.4 Foul drainage 2.5 Scaffolding Chapter 3 AT A GLANCE 3 Ground Stability and Foundations 3.1 Bedrock and soil types 3.2 Ground stability 3.3 Foundations: Functional requirements 3.4 Foundation construction 3.5 Strip foundations 3.6 Pad foundations 3.7 Raft foundations 3.8 Short‐bored pile foundations 3.9 Precast pile and beam foundation systems

1 2 5 6 8 11 12 15 17 17 30 34 41 68 91 93 93 100 104 116 126 137 145 153 155

v

vi  Contents

Chapter 4 AT A GLANCE 4 Floors 4.1 4.2 4.3 4.4 4.5 4.6 4.7

Functional requirements Ground‐supported concrete floor slab Suspended concrete floor slabs Suspended timber ground floors Reinforced concrete upper floors Timber upper floors Floor finishes

Chapter 5 AT A GLANCE 5 Loadbearing Walls 5.1 Functional requirements 5.2 Walling materials 5.3 Mortar 5.4 Bonding bricks and blocks 5.5 Damp‐proof courses (DPCs) 5.6 Solid wall construction 5.7 Cavity wall construction 5.8 Internal and party walls 5.9 Straw wall construction 5.10 Earth wall construction Chapter 6 AT A GLANCE 6 Roofs 6.1 Functional requirements 6.2 Pitched roofs 6.3 Pitched roof coverings 6.4 Sheet metal covering to low‐pitched roofs 6.5 Thermal insulation to pitched roofs 6.6 Flat roofs 6.7 Timber flat roof construction 6.8 Concrete flat roofs 6.9 Thermal insulation to flat roofs 6.10 Parapet walls 6.11 Green roofs 6.12 Roof drainage Chapter 7 AT A GLANCE 7 Windows 7.1 Functional requirements 7.2 Window types

157 159 159 162 170 176 179 184 193 203 205 205 212 223 227 233 241 270 298 299 305 311 313 313 317 338 356 359 365 367 384 387 392 396 400 409 411 411 436

Contents  vii

7.3 Window frames 7.4 Glass and glazing 7.5 Hardware 7.6 Window cills

446 473 488 489

Chapter 8 AT A GLANCE 8 Doors

497 499

8.1 Functional requirements 8.2 Door types 8.3 Door frames and linings 8.4 Hardware Chapter 9 AT A GLANCE 9 Stairs and Ramps 9.1 Functional requirements 9.2 Materials, terms and definitions 9.3 Types of stairs 9.4 Timber staircases 9.5 Stone stairs 9.6 Reinforced concrete stairs 9.7 Structural glass stairs 9.8 Ramps Chapter 10 AT A GLANCE 10 Surface Finishes 10.1 Functional requirements 10.2 Wall and ceiling finishes 10.3 Skirtings, architraves and kitchen cabinets 10.4 Tiling to walls 10.5 Painting and decorating Chapter 11 AT A GLANCE 1 1 Internal Environment and Energy Supply 11.1 Principles and performance requirements 11.2 Heat loss calculations 11.3 Indoor climate control 11.4 Energy sources 11.5 Solid fuel–burning appliances 11.6 Domestic gas installations 11.7 Domestic electrical supply and installations 11.8 Artificial lighting 11.9 Testing and monitoring thermal performance

499 504 525 540 547 549 551 553 562 563 574 576 580 581 585 587 587 589 604 608 609 617 619 619 621 632 636 641 657 662 680 683

viii  Contents

Chapter 12 AT A GLANCE 12 Water Supply and Sanitation 12.1 Cold water supply and distribution 12.2 Hot water supply and distribution 12.3 Water services to multi‐storey buildings 12.4 Pipes for water supply 12.5 Sanitary appliances Index

689 691 691 700 708 717 721 743

Preface

Robin Barry’s Construction of Buildings first appeared in print in 1958 and e­ ventually grew into five volumes. When I took on the task of revising and updating the Barry books, a decision was taken to condense the work into two volumes to make it more accessible to readers. This was a big task, and it required the input of a former colleague, Christopher Gorse, and the help of many individuals and companies, for which I remain extremely grateful. Working on the books continues to be a process of addition and subtraction to keep the content topical and informative to a wide readership. Now, as a solo‐authored work, it has been possible to further simplify and clarify the content while making the latest round of revisions. This has resulted in repositioning of material and new features, such as ‘How to navigate this book’ and the ‘At a glance’ fact sheets. The repositioning of material, from one volume to another, and within volumes, has helped to ensure a more logical flow of information that better reflects the process of construction. The main changes to each volume are as follows. This volume has retained the same chapter structure, with changes made within chapters to improve readability. The introductory chapter has been rewritten to better explain the process of construction and to place greater emphasis on its environmental impact. The material on timber‐framed construction has been moved to the Advanced volume, which has allowed for simplification, rewriting and renaming of Chapter 5 to better reflect the content on loadbearing wall c­ onstruction. Scaffolding can now be found in this volume, and the material on foundations has been restructured in both volumes to remove repetition. The Advanced volume has been restructured. Offsite construction has been rewritten and moved to the front of the book (Chapter 2), since most of the m ­ aterial in the volume is concerned with prefabricated and preassembled construction. There is a new chapter on framed timber construction (Chapter 5); thus, the three main materials for framed construction – timber, concrete and steel – are now in the same volume, ­making it easier for readers to draw comparisons. The material relating to existing buildings, demolition and recycling has been moved to Chapter 11, thereby completing the entire building lifecycle. In making these revisions, the original philosophy of Robin Barry – to address the functional requirements of building elements – has been retained. Regardless of building type, the functional requirements of the main elements remain r­ elevant. Similarly,

ix

x  Preface

the underpinning construction principles remain much the same, despite ­ever changing building codes, regulations, guidance and better awareness of the environmental impact of buildings. Professor Stephen Emmitt Department of Architecture and Civil Engineering University of Bath, UK

How to Navigate this Book

The Barry books are presented in two volumes, Introduction and Advanced, with the volumes designed to complement one another. The titles are used to reflect the stage at which these subjects are taught in colleges and universities in the UK. Introduction ­covers the first year, primarily dealing with loadbearing construction and domestic scale ­developments. It also covers the common elements found in most buildings. The Advanced volume includes material usually taught in the second to third year, primarily dealing with offsite techniques and framed construction for larger buildings. Combined, the two volumes take the reader through the entire life cycle of a b ­ uilding – from inception and construction; to the building in use; and the eventual demolition, recycling and reuse of valuable resources. An overview of the chapters in each volume is provided in Table  1 as an aid to ­navigating the books. Chapters are designed such that they can be read from front to back or they can be dipped into as the need arises. Each chapter or section introduces the primary ­functional requirements, and then the reader is introduced to an increasing level of detail. The illustrations and photographs are provided to enhance our understanding of the main principles. ‘At a glance’ sheets are used for each chapter to address the main ‘what’, ‘why’, ‘how’ and ‘when’ questions.

Table 1  Overview of the chapters Chapter 1 2 3 4 5 6 7 8 9 10 11 12

Introduction Introduction Site Analysis, Set‐Up, Drainage and Scaffolding Ground Stability and Foundations

Advanced Introduction Offsite Construction

Pile Foundations, Substructures and Basements Floors Single‐Storey Frames, Shells and Lightweight Coverings Loadbearing Walls Structural Timber Frames Roofs Structural Steel Frames Windows Structural Concrete Frames Doors Envelopes to Framed Buildings Stairs and Ramps Lifts and Elevators Surface Finishes Fit Out and Second Fix Internal Environment and Energy Supply Existing Buildings: Pathology, Upgrading and Demolition Water Supply and Sanitation

xi

xii   How to Navigate this Book

If readers are studying, for example, loadbearing construction, then they will need to read the Introduction volume and focus on specific chapters to supplement their learning in the classroom. In this situation, the reader will need to read chapters all the way through in the first instance, perhaps returning to specific issues, such as the position of damp‐proof courses. Similarly, if readers are studying framed construction, the Advanced volume will be a valuable resource, supplemented with material on, for example, doors and windows from the Introduction volume. When it comes to revising for examinations in construction technology, the ‘At a glance’ feature will be useful in prompting one’s memory, prior to revisiting key issues within the chapter. When readers use the books to help detail their building designs, dipping into the chapters to see solutions to typical detailing problems will help with understanding. It is, however, important that we understand the principles underlying the construction of buildings – what needs to be achieved, and why. Thus, the details and photographs provided give an indication of how it could be done, and not how it should be done.

1

Introduction

The aim of this introductory chapter is to highlight some of the factors that determine how buildings are constructed and also to provide some context to the chapters that follow. Related issues are dealt with in the introduction to Barry’s Advanced Construction of Buildings. A brief overview of the building process and the function and performance of buildings leads into a discussion about responding to climate change. This is followed by a description of the general principles of construction, concluding with some comments on legislation, sources of information and making informed choices.

1.1  The construction process In simple terms, the process of design and construction starts with a want or need. This may relate to, for example, a new building, or extension, repair and/or alteration of an existing structure. These wants and needs are translated into a set of requirements, a written ‘brief ’ that informs the design team. The design team will develop a conceptual design and increase the level of detail to such an extent that a constructor can interpret written and drawn instructions to realise a physical artefact. The constructor will bring together appropriate resources – people, materials and machinery – to realise the design safely and within the agreed parameters of time, cost and quality. This process, or more correctly this series of interlinked processes, involves a large number of people working towards a common goal. This requires a collaborative and integrated approach to deliver the project and the product (building) to the expectations of the client. It also requires a collective understanding of many issues, including construction technology. The process of design and construction is extensively covered in the literature on design management, project management and construction management, and therefore it does not need to be repeated here. However, it is necessary to make the point that we rarely make decisions in isolation when designing and constructing buildings. The nature of collaboration is determined by the type of procurement route used for a project and the success of  the interactions between the organisations and individuals assembled to realise the ­project. The process is aided by information communication technologies (ICTs) and building information models (BIMs), and conducted within a legislative framework. Digital ­technologies allow project contributors to communicate regardless of physical location and to work collaboratively on the design and construction via a shared virtual BIM. The legislative framework includes regulations and guidance relating to fire protection, health Barry’s Introduction to Construction of Buildings, Fourth Edition. Stephen Emmitt. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd. 1

2   Barry’s Introduction to Construction of Buildings

and safety, the wellbeing of workers and building users, and the protection of our ­environment. Our decisions are also influenced by the physical site on which the building is to be constructed, as well as the availability of materials and technologies to realise the building in an ethical manner. Genius loci – the importance of site Buildings exist within a local context, and they should be designed, detailed and c­ onstructed to be in harmony with nature – that is, they should respond to their genius loci in a positive and sustainable way. Understanding the physical characteristics of the site and its unique  microclimate is fundamental to designing and constructing a building that is in ­balance with its environment. The importance of site characteristics becomes even more critical with some of the alternative approaches and technologies that may be more prone to damage from, for example, water. Sensitivity to the site is a crucial factor in ensuring a durable and trouble‐free building. It follows that the proposed site of the building must be carefully analysed in terms of the microclimate, soil type, position of water table, etc. Then, and only then, should we start to design and make decisions about the most appropriate materials and construction techniques to realise the project within the given parameters of time, cost and quality. Site analysis is described further in Chapter 2.

1.2  The function and performance of buildings Buildings are designed, constructed, altered, upgraded, restored or demolished for a variety of reasons. Whether the aim is simply to provide more space or to make a financial gain from speculative development, all building projects need to fulfil a function and meet set performance criteria, no matter how fundamental or sophisticated the client’s requirements may be. The function of the building, be it, for example, a house, school or, hospital, will influence its design and architectural appearance. Similarly, the performance requirements will influence the type of materials and technologies used to realise the building, factors that also influence the building’s architecture. Both the function of the building and the performance requirements are initially determined through discussions with the client at the briefing stage. The briefing process aims to establish what the client wants and why. The written brief will set out the type of building required and its primary function. Performance requirements, such as the thermal performance of the building, size of rooms, etc., will also be stated, along with a financial budget, timescale for completion of the project and the required level of quality. The brief informs and guides the design team. As the design develops, attention will turn to the function of individual building elements and components and their assembly to meet the agreed performance requirements safely and efficiently. This involves interaction with specialists, manufacturers and constructors to harness knowledge and expertise to the benefit of the building’s design and construction. Function The primary function of a building is to provide shelter from the weather, and as a container for living, working and playing in. This involves understanding how people will use the building and the equipment required to support the comfort and wellbeing of the

Introduction  3

­ ccupants over a long time period. Thus, the daily activities that will take place within and o around the building will influence the building’s function. The principal functional requirements may be broken down into the following: ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏

Provide shelter, security and privacy Provide structural and fire safety Ensure thermal comfort and wellbeing Have low environmental impact Be easy to use and operate (functionality) Be easy to maintain, repair and replace/upgrade Be adaptable and durable Be able to reuse and recycle materials and components at a future date

The overall goal is to achieve these functions in an economical, safe and timely fashion using the most appropriate resources available and with minimal negative impact on the environment. These primary functional requirements are explored in the chapters that ­follow in relation to specific building elements – for example, walls and windows. Performance In construction, the word ‘performance’ is used to describe: (1) the performance of the design and construction team, known as ‘project performance’, and (2) the performance of the building, known as ‘product performance’. In this book, the focus is on the performance of the building, although the manner in which the design and construction team ­performs  –  the decisions made and the actions taken  –  will impact upon the overall ­performance of the building. The design and construction of the building will influence how the users of the building are able to perform their tasks. Good design and construction will encourage positive performance and wellbeing, whereas poor design and construction will have a negative influence on performance and wellbeing. Performance requirements will be specific to the client, the unique physical building site and the time of construction. Thus, performance requirements will vary from project to project, from site to site and over time. However, the main considerations are likely to be: ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏

Space, determined by the floor area and/or volume (and related to anticipated use) Thermal, visual and acoustic performance (quality of indoor climate) Design life and service life of the building and specific building components/elements Cost of construction, cost of use and cost of demolition/deconstruction and recycling Quality of the finished building (functionality, durability and usability) Appearance of the finished building (aesthetics) Environmental impact and ethical resourcing of materials and components Adherence to prevailing legislation and codes

Other specific performance criteria will relate to the use of the building – for example, the provision of special work surfaces for catering establishments. Legislative performance requirements are set out in building codes and regulations (see the section titled ‘Building

4   Barry’s Introduction to Construction of Buildings

control and building regulations’). Specific performance requirements – for example, the thermal insulation of walls and fire protection of doors – must be met or bettered in the proposed construction method. Quality Function and performance will influence the quality of the building. The quality of the completed building, as well as the process that brings it about, will also be determined by the quality of thought behind the design process, the quality of the materials and products specified, and the quality of the work undertaken. There are a number of different quality issues: (1) Quality control is a managerial tool which ensures that both work and products c­ onform to predetermined performance specifications. This applies both to the design and the construction phases. Getting the performance specification right is an important step in achieving the required quality, be it for an individual component or the whole building. (2) Quality assurance is a managerial system that ensures quality service to predetermined parameters. The ethos of total quality management aims at continual improvement and greater integration through a focus on client satisfaction. Manufacturers, contractors and professional consultants use this. (3) Quality of the finished artefact will be determined by several variables that are constant for all projects – namely, the: ❏❏ Interaction and characteristics of the participants engaged in design, manufacture and assembly ❏❏ Effectiveness of the briefing process ❏❏ Effectiveness of the design decision‐making process and resultant information ❏❏ Effectiveness of the assembly process ❏❏ Effectiveness of communications ❏❏ Time constraints ❏❏ Financial constraints ❏❏ Manner in which users perceive their built environment The required quality of materials and workmanship will be set out in the written s­ pecification. Good‐quality materials and good‐quality work tend to carry a higher initial cost than lower‐quality alternatives. However, the overall feel of the building and its long‐ term durability may be considerably improved – we tend to get what we pay for. When making decisions about the materials and components to be used, it is important to consider the whole‐life cost of the materials, and not just their initial capital cost and the cost of labour to assemble the materials. Economics The building site and the structures constructed on the land are economic assets. They have a value to the owner, building users and society at large. In addition to the cost of the land, there are three interrelated costs to consider.

Introduction  5

The first is the initial cost – that is, the cost of designing and erecting the building. This is usually the primary and sometimes the only concern of clients and developers. It covers professional fees and the costs associated with land acquisition and permissions, the capital cost of materials and components, and the labour costs associated with carrying out the work. Material costs are prone to wide swings in price depending on the market, and it may sometimes be necessary to adjust the design to suit the supply and price challenges. An example would be to change from a steel frame to a concrete frame because of the shortage, and hence higher‐than‐anticipated cost, of steel. Labour costs comprise a substantial part of the initial cost of most building projects and are related to the type of construction technologies to be used, be it site based or offsite. Ideally, we should be aiming to use local labour and locally sourced materials to reduce the carbon footprint of the building and to help stimulate the local economy. The second cost to consider is the cost of the building in use – that is, the costs associated with routine maintenance and replacement, and the costs associated with heating and ­servicing the building over its life. These costs can be reduced by sensitive design and detailing – for example, designing a building to use zero energy and to be easy to maintain will carry significant cost benefits over the longer term (not to mention benefits to the environment). All materials and components have a specified design life and should also have a specified service life. Designers and contractors need to be aware of these factors before starting work, thus helping to reduce future maintenance requirements. The third cost is the cost of materials recovery at the end of the life of the building – that is, the cost of demolition, recycling and disposal. Although it may be difficult to predict exactly when the building is likely to be substantially remodelled or dismantled, this should still be an important consideration when detailing and constructing the building. All three areas of cost associated with a building project should be considered within a whole‐life cost model, from which decisions can be made about the type of materials and components to be used and the manner in which they are to be assembled (and ­subsequently disassembled). This links with issues concerning maintenance, repair renovation and recycling.

1.3  Building: the (de‐carbonised) product Adopting the philosophy of ‘leaving this planet in a better state than we found it’ requires an understanding and appreciation of the environmental impact of construction and ­buildings. In many cases, this requires a change in how we think about building, how we construct buildings, how we use buildings and how we dismantle and reuse valuable materials. While the focus is often on the amount of energy used in construction (embodied energy) and the amount of energy used to service buildings once they have been c­ onstructed, we also need to reduce the amount of material waste produced during the construction process. The message is that we must do more to build in a way that has the least negative impact on our natural environment. The environmental impact of buildings will be influenced by many factors – starting in the design phase and moving to construction to include issues such as the responsible (e­thical) sourcing and manufacturing of environmentally sustainable materials and

6   Barry’s Introduction to Construction of Buildings

building products; the (informed) decisions taken during the construction process; the actions of owners and occupants through a long period of use, including decisions relating to maintenance, repair, alteration and reuse; through to deconstruction and the recovery of valuable materials and components at the end of the building’s useful life. At this stage, materials and components can be reused in new projects, or recycled for use in new building products, helping to reduce the amount of material sent to landfills and  improving the environmental impact of buildings. We should seek to minimise ­environmental impact through sensitive design and material selection, which requires a thorough understanding of building construction. The mantra is to: ❏❏ ❏❏ ❏❏ ❏❏

Reduce Reuse Recycle Revitalise

To decarbonise the built environment, we need to consider the amount of energy used at all stages in the life of a building. This includes the energy expended in the extraction, working and transportation of materials to the site and the total resources used during construction. This should be included in the calculation of the building’s embodied energy. The choice of components and the way in which they are brought together to make a building will ­influence the energy consumption of the building in use and the ease or otherwise of dismantling the building at a future date with minimal energy use. The drive to decarbonise the built environment is driving innovation in building technologies and materials and helping to raise questions about how we build.

1.4  Responding to climate change Although we cannot accurately predict the future impact of climate change, the general consensus is that, in the UK, the average temperature will rise, as will the amount of rainfall and the average wind speed. The message from the weather forecasters is wetter, warmer, windier and more ‘extreme’ weather. This has given rise to a number of concerns about the suitability of the existing building stock and also about the construction technologies employed for new buildings. How, for example, do these predicted changes impact on the way in which we detail the external fabric of buildings? Are existing codes, standards and building practices adequate? The general consensus is that we should adopt a cautious approach, although we should also resist over‐detailing and over‐specifying, which may be wasteful. Concern has been expressed about new buildings, especially homes that are built from lightweight materials, such as timber‐framed, steel‐framed, modular and other lightweight construction systems. The fear is that, with the expected increase in temperatures, the ­internal temperature of lightweight construction may become too high during the summer, thus necessitating air conditioning (increased energy demands) and/or better shading and natural ventilation. Buildings constructed with heavy walls, with small windows and sun shading devices (e.g. shutters, verandas), are less susceptible to temperature fluctuation. However, there are plenty of places around the world that have a warmer climate than the

Introduction  7

UK and where lightweight construction is used successfully. The answer to the problem is not so much about the type of construction used as it is about the manner in which the building is designed to respond better to its immediate environment (e.g. by building in verandas and shading devices). Passive design includes the selection of energy‐efficient building materials, so that there is very little or no need to provide heating (or cooling) of the interior space. This is referred to as a ‘fabric first’ approach to design and construction. An example is Passivhaus (German for ‘passive house’), a building standard that effectively eliminates the need for space heating by using a highly insulated building fabric. Taking this c­ oncept a little further, the Activhaus (‘active house’) standard aims to design and construct a building that generates more energy than it uses. Buildings that are constructed using straw bales and rammed earth adopt the ‘fabric first’ philosophy to eliminate the need for space heating. There are a variety of approaches to ecological (alternative) construction. Some have their roots in vernacular architecture and others in technological advancement, although most approaches and products combine features present in both old and new construction techniques. Strategies adopted can include, for example, the reuse of salvaged components and recycled materials from redundant buildings, designing buildings that may be disassembled with minimal damage to the components used and buildings that are designed to ‘decompose’ after a predetermined time frame. We urge readers to look beyond the familiar and explore more ecological approaches to the construction of buildings. Energy efficiency and environmental performance In attempting to reduce the amount of carbon produced by buildings during their lifetime, we need to consider many issues. As a minimum, we should be aiming to: Reduce the running costs of buildings (by reducing energy use) Enhance air quality (natural ventilation) and maximise natural daylight Select low‐allergy and environmentally friendly materials Improve water efficiency and increase (greywater) recycling Design in the possibility of adaption and alteration (thereby reducing wastage of ­materials at a future date) ❏❏ Promote future‐proofing (by employing easily upgradable, energy‐efficient technologies)

❏❏ ❏❏ ❏❏ ❏❏ ❏❏

If these (and related) factors are addressed at the conceptual and detailed design phases, then the initial cost of construction is likely to be similar to that of a less energy efficient and less environmentally friendly project. Add to this the considerable cost savings over the life of the building, and it is difficult to understand why many buildings are still being constructed with such scant regard for the whole‐life performance of the constructed works. Our existing buildings are a little more problematic, simply because it may be a challenge to make improvements to the building fabric and services to improve their environmental impact. This is particularly challenging when buildings are located within conservation areas and/or are designated as being of historic interest (e.g. those having ‘Listed’ status). The ability to upgrade the building fabric and retrofit appropriate technologies is addressed in Barry’s Advanced Construction of Buildings.

8   Barry’s Introduction to Construction of Buildings

1.5  General principles of construction Regardless of the approach taken in the design and construction of buildings, there are several fundamental principles that hold true. The primary principle is that the building must resist gravity and hence remain safe throughout its design life. It also must resist the weather to provide a safe, healthy and durable structure. This is achieved by employing loadbearing or framed construction, comprising the following common elements: ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏

Foundations (see Chapter 3) Floors (see Chapter 4) Walls (see Chapter 5) Roof (see Chapter 6) Windows and doors (see Chapters 7 and 8) Stairs and ramps (see Chapter 9) Surface finishes (see Chapter 10) Services, energy supply and thermal comfort (see Chapters 11 and 12)

It is vital for the success of the building project and the performance of the constructed building that an integrated approach be adopted. It is impossible to consider the choice of, for example, a window without considering its interaction with the wall in which it is to be positioned and fixed, maintained and eventually replaced. It follows that the window should exhibit the same, or very similar, thermal and acoustic performance characteristics as the wall. The same argument holds for all building services, which should be integrated with the building structure and fabric in such a way as to make access for routine maintenance, repair and upgrading a safe and straightforward event that does not cause any damage. Loadbearing or framed construction? A fundamental question for many designers, engineers and constructors relates to which type of construction to use – loadbearing or framed. Masonry loadbearing construction is well established in the British building sector, and, despite a move towards offsite construction and prefabrication, loadbearing construction tends to be the preferred option for many house builders and small commercial buildings. The two approaches are solid wall construction and, more typically, cavity wall construction. In a typical loadbearing cavity wall construction, the main loads are transferred to the foundations via the internal loadbearing wall made of blocks or bricks. The internal wall may also be constructed from timber or metal frames. In both cases, the external skin serves to provide weather protection and aesthetic quality. Primarily, ‘wet’ construction techniques are employed for bricklaying, plastering and so on. Quality control is highly dependent on the labour used and the quality of the supervision on site. Framed construction has a long pedigree in the UK, starting with the framed construction of low‐rise buildings from timber and followed by early experiments with iron and reinforced concrete frames. Subsequent technological developments and advances in production have resulted in three main materials being used: timber, steel and concrete (see Barry’s Advanced Construction of Buildings). Framed construction is also suited to prefabrication and offsite manufacturing. Dry techniques are used, and quality is easier to control because the

Introduction  9

­ roduction process is repetitive and largely carried out in a ­carefully controlled factory p ­environment. Site operations are concerned with the correct placement and connection of individual pre‐assembled component parts in a safe and timely manner. Design and constructability The functional and performance requirements will inform the design process, from the initial concepts right through to the completion of the detailed designs and production of the information (drawings, schedules and specifications) from which the building will be constructed. The design of the junction between different materials, that is, the solution for how different parts are assembled, is crucial in helping to meet the performance and ­functional requirements of the overall building. Good design and detailing will help the contractor and subcontractors in assembling the building safely and economically. Good design and detailing, combined with good workmanship, will contribute to the durability and ease of use of the building over its life. The manner in which materials are joined together will be determined by their material properties, shapes and sizes available, types of joints required, construction method (e.g. framed or loadbearing) and the safe sequence of assembly (and anticipated disassembly). Interfaces between materials and components can be quite complex and will be specific to particular materials and components. However, in simple terms, the following methods are used widely to join separate parts, either in isolation or in combination: ❏❏ Gravity. The simple placing of materials so that they stay in place due to their mass (e.g.

stone on stone) or shape (e.g. interlocking roof tiles) is common, although it tends to be used in conjunction with an adhesive joint or mechanical fixing. Masonry is usually laid in mortar in loadbearing construction, and roof tiles need to be clipped in position at regular intervals. ❏❏ Screws and bolts. Screws and bolts perform a similar function in joining two (or more) materials together by a mechanical fixing. Screws are widely used for joining timber, with the thread of the screw drawing the timber components together through the act of screwing through one piece of the material into the other. Bolts tend to be used for joining two pieces of metal and are (usually) placed in pre‐drilled holes. A nut is threaded onto the end of the bolt, and the bolt and nut are tightened to hold the materials together. The advantage of screws and bolts is that it is relatively straightforward to unscrew the screw or undo the bolt with minimum damage to the materials. Both screws and bolts can be reused. This is helpful for routine maintenance and inspection, and also for recovering materials and reusing them at a future date. ❏❏ Nails. Nails are driven through the first material into the second using a hammer or a nail gun, with the materials held together by friction. This is a common method of joining two materials together, although it is difficult to withdraw the nail without causing damage to the materials and the nail. ❏❏ Adhesives, glues and welds. A wide variety of materials are employed to stick or bond one material to another. These include lime and cement mortars, chemical adhesives, glues and welds. Unless the bond is designed to be comparatively weak in comparison with the materials being joined together (e.g. lime mortar in brickwork), it will be very difficult to disassemble the construction without damaging the materials.

10   Barry’s Introduction to Construction of Buildings

❏❏ Mastics. Mastics are primarily used to fill joints. These ‘flexible’ filling materials are

designed to allow movement between adjacent materials and to prevent the penetration of rain and wind through the joint. Mastic materials are usually forced into the joint, often making them difficult to remove, although this varies, depending on the material used and the shape of the joint.

Constructability (or buildability) is an approach to building design and construction that seeks to eliminate non‐productive work on site, make the production process simpler and  provide the opportunity for more efficient site management and safer working. Thus,  designing and detailing for constructability requires an understanding of how ­components are manufactured off site, as well as how the building is to be assembled (the sequence of work packages) on the site. The core message of constructability is more simplicity (of joints between materials), greater standardisation (to avoid unnecessary cutting on site, and hence reduce material waste) and better communication between designer, manufacturer and builder. These three principles also relate to the eventual disassembly of the building, when materials and building products will be recovered, reused and recycled. An ethical approach should be taken to the sustainable sourcing of all ­building materials and products, which means that those making the decisions about which materials and products to specify and purchase must understand the supply chain and seek assurances about the provenance of each and every item. Some of the practical considerations are concerned with: ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏

Timescale Availability of labour and materials (supply chain logistics) Sequence of construction and tolerances (constructability) Reduction of waste (materials, labour, time and energy) Temporary protection of workers and materials from the weather Integration of structure, fabric and services Maintenance and replacement Disassembly and recycling strategies

Prefabrication and offsite production In recent years, the emphasis in construction process improvement has been on prefabrication and offsite production. With the rapid uptake of BIMs and advances in digital manufacturing, the opportunities for using offsite production are more obvious than they may have been previously. While offsite production is still best suited to repeat building types and repeat components and elements of buildings, such as toilet and bathroom pods, it is sometimes also feasible to use offsite production for bespoke projects. Improvements in product quality and health and safety may be made by using prefabricated components and proprietary systems. This has tended to move the labour skills away from the building site into the controlled environment of the factory. Site operations become limited to the lifting, positioning and fixing of components into the correct position, and the emphasis is on the transportation of components from the factory to the site when required, and not before. Offsite construction is described more fully in Barry’s Advanced Construction of Buildings.

Introduction  11

1.6  Regulations and approvals A number of approvals need to be in place before building work commences. The two main consents required in the UK are from the appropriate town planning authority and building control. Specific conditions relating to town planning consent and building regulation approval will be influenced by the physical characteristics of the site and its immediate surroundings. Planning consent Issues concerning local town planning approval are outside the scope of this book. However, it is important to understand that (with a few exceptions) planning approval must be applied for and have been granted before any construction or demolition work commences. The legislation concerning the right to develop, alter and/or demolish buildings is extensive, and professional advice should be sought before applying for the appropriate approvals. The process of obtaining approval can be very time consuming (preparing the necessary information for submission, allowing time for consultation and decisions, etc.), and conditions attached to the approval may affect the construction process (e.g. restricted times of  working, conditions on materials to be used, etc.). The application may sometimes be  unsuccessful, leading to an appeal or the submission of a revised proposal. Planning consent will permit development; it does not deal with how the building is to be constructed safely; this is dealt with by building control. Building control and building regulations In the UK, building control is governed by differing, though broadly similar, sets of legislation, for England, Wales, Northern Ireland and Scotland, respectively. Building regulations aim to ensure the health and safety of people in and around buildings by setting functional requirements for the design and construction of buildings. The regulations also aim to promote wider concerns, such as low environmental impact and the wellbeing of building occupants. In England and Wales, the Building Act 1984 and Building Regulations 2010 set out minimum functional requirements for buildings and the health and safety requirements that may be met through the practical guidance given in the Approved Documents. These in turn refer to British and European Standards and Codes of Practice. In Northern Ireland, construction is covered by the Building Regulations (Northern Ireland) 2012 with Approved Documents, similar to those for England and Wales. In 2014, the Welsh Government brought in a series of changes that now differ from the regulations in England, with the changes binding from April 2017. In Scotland, the Building (Scotland) Act 2003, which came into force in 2005, has replaced the old prescriptive standards with performance standards. The Act is a response to European harmonisation of standards and their use in Scotland as required under the Construction Products Directive (CPD). The Act has two objectives: to allow greater flexibility for designers in meeting minimum performance standards, and to ensure greater consistency across the country. There are separate Guidance Documents for domestic and non‐domestic buildings, both of which are divided into six subject areas that match the essential requirements of the CPD – namely, structure, fire, environment, safety, noise and energy.

12   Barry’s Introduction to Construction of Buildings

The Approved/Guidance Documents give practical guidance to meeting the requirements, but there is no obligation to adopt any particular solution in the documents if the stated functional requirements can be met in some other way. The stated aim of the current regulations is to allow freedom in the choice of building form and construction, so long as the stated (minimum) performance requirements are satisfied. In practice, the likelihood is that the majority of designers will accept the guidance given in the Approved/Guidance Documents as if the guidance were prescriptive. This is the easier and quicker approach to construction, rather than proposing some other form of construction that would involve calculation and reference to a bewildering array of British Standards, Codes and Agrément Certificates. Although the guidance in this book is intended to be as broad as possible, both for consistency and to avoid confusion, reference is made only to the Approved Documents for England. However, the principles for readers in the UK are broadly similar, with differences in detailing buildings arising from a combination of legislation, response to local climate and building tradition. Full details of the Acts as well as the current versions of the Approved Documents and Guidance Documents are available online (http://www.planningportal. gov.uk; http://www.planningportal.co.uk/wales; http://www.beta.gov.scot; http://www. buildingcontrol‐ni.com). Health and safety legislation In addition to the legislation set down in the Building Regulations, other legislations affect the way in which buildings are designed and constructed. For example, health and safety and fire safety legislation are covered in a number of documents that sit alongside the Approved/Guidance Documents. The European Union is particularly active in promoting consistent standards across the Union through a series of directives. For example, the European Union Council Directive 89/106/EEC (1988), the CPD, requires all construction products to satisfy the Essential Requirements, which deal with health and safety issues – namely, mechanical resistance and stability; safety in case of fire; hygiene, health and environment; safety in use; protection against noise; and energy economy and heat retention. Over 600 CEN standards have been mandated under the CPD. In addition to this, there exists a large body of Codes and guidance documents. Health and safety, along with the wellbeing of workers, is covered under a variety of ­statutes and guidance. In the UK, the Construction (Design and Management) Regulations 2015 came into force on 6 April 2015. The regulations set out what people need to do to protect themselves and others from harm when engaged in construction work. Full details and associated advice can be found on the Health and Safety Executive homepage (www.hse.gov.uk/construction). Good health and safety starts early in the design phase and ­continues into the detailing of a building, so that it can be assembled, maintained and dismantled in a safe manner. Constructors need to plan the work to manage the risks involved, and also engage with the workforce about the risks and how they are being managed.

1.7  Making choices and sources of information The design and construction activities of buildings are concerned with making informed choices. Decisions have to be made about the design of the building and its details, which necessitates the selection of materials and components to realise the design intention and

Introduction  13

aspirations of the client. At the construction stage, decisions have to be made about what mechanical plant to use, how best to sequence the work so that operations are conducted safely and efficiently, and what to do when an unexpected problem occurs. During the life of the building, decisions will need to be made about how best to replace damaged or worn components and how to upgrade buildings to improve their functionality and performance. Then, at the end of the building’s useful life, decisions will need to be taken about how to  deconstruct the building safely and economically while also maximising the reuse of materials, products and components. The contents of this book and Barry’s Advanced Construction of Buildings are designed to assist with that decision‐making exercise. Sources of information Construction is essentially a process of assembly where products are chosen from manufacturers’ catalogues and/or from the builders’ merchants and are put together using a raft of different fixing techniques. Each new project brings with it a new set of challenges and a fresh search for information to answer specific problems. Some of the main sources of information for readers working in the UK are: ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏

Building Regulations and Codes British (BS), European (EN) and International (ISO) standards British Board of Agrément (BBA) certificates Building Research Establishment (BRE) publications Trade association publications Manufacturers’ technical literature Compendia of technical literature Technical articles and guides in professional journals Building information centres Organisational knowledge (codified in ‘standard’ details and specifications)

Readers should make use of the information and details provided by manufacturers, but should avoid making a choice based on information from any one source. Explore at least three different suppliers to compare functional and performance requirements, including costs and availability – and then compare this with current legislation and standards – thus making an informed decision based on achieving the best value within given parameters. A note of caution Before proceeding any further, it is necessary to make an important observation about the contents of this book and Barry’s Advanced Construction of Buildings. The principles and details illustrated here are intended as a guide to the construction of buildings. Details should not be copied without thinking about what is really going on. This also applies to details given in guidance documents. Readers should be asking questions such as: How is the building to be assembled, maintained and disassembled safely and efficiently? Is the detail in question entirely suitable for the task at hand? We make this point because approaches to detailing and construction vary from region to region (e.g. a building located in a wet and sheltered area of the UK may benefit from a pitched roof with a large overhang, but a similar building in a dry and exposed part of the country may benefit from a

14   Barry’s Introduction to Construction of Buildings

pitched roof with clipped eaves or even a flat roof). Building practices and regulations also differ from country to country (e.g. differences between the regulations relating to England and Wales), and so it is impossible to cover every eventuality for every reader. Instead, we would urge readers to engage in some critical thinking, analyse the details and seek out alternative (more sustainable) approaches and products. At a practical level, we need to work closely with consultants, manufacturers and suppliers with the aim of applying specialist ­knowledge to the benefit of the construction process, thinking critically and making informed decisions.

Site Analysis, Set‐Up, Drainage and Scaffolding: Chapter 2 AT A GLANCE What?  The main purpose of site analysis is to identify the physical features of the site, its micro‐climate and legal constraints relating to the proposed development. This influences design decisions and also helps to reduce the risks associated with the proposed development. Site set‐up is required to make the site safe prior to construction and/or demolition, and includes the provision of welfare facilities for workers and visitors. Early site activities include ground preparation, site drainage and the construction of foul drainage. Scaffolding will be required to allow safe working at heights above ground level. Why?  Without a thorough site analysis, it is not possible to make informed decisions

about the positioning, design, material selection and construction of the building. Site set up will be specific to each site, with the location of site access, site welfare cabins and temporary storage areas determined by the physical characteristics of the site. Site drainage and foul drainage is usually undertaken before, or alongside, the construction of the building foundations. The amount and type of scaffolding required for the safe construction of the building will be influenced by the building design and the amount of offsite prefabrication to be used.

When?  The site analysis should, ideally, be conducted prior to the client acquiring the site, but must be done before design commences. Data collected will inform the building design and the manner in which the building is to be constructed. Site set‐up will commence once the client has legal possession of the site and is ready to proceed with the development (i.e. relevant permissions are in place). Site accommodation and scaffolding will be required for the duration of the work. Site drainage and foul drainage will be scheduled to suit specific site conditions and to suit the foundations design. How?  A number of techniques may be used to collect appropriate information. This

ranges from desktop studies to walk over inspections of the site and detailed physical surveys. Site set‐up will consist of secure fencing and the creation of controlled access points for personnel, delivery vehicles and plant. Welfare facilities and areas for temporary storage of materials will be located to suit the physical characteristics of the site and the planned flow of work. Site drainage and associated groundwork will help to make the site ready for the construction of the building’s foundations. For new build projects, it is common to erect the scaffolding as the work proceeds. For work to existing buildings, it is usual to erect the scaffolding to allow safe access to all relevant levels and areas prior to the commencement of work.

15

2

Site Analysis, Set‐Up, Drainage and Scaffolding

The physical characteristics of the site and its micro‐climate will influence the decisions made about a building’s design and construction. A thorough site analysis must be completed before any design or construction work commences. Information gleaned from the site analysis can be collated into a performance appraisal document, from which informed decisions may be made by the design and construction team(s). Once the design is complete and approved by the client, relevant town planning and building control approvals are in place, and the contractor has legal possession of the site, work can commence to prepare the site for construction. This is known as the site set‐up phase. This will involve making the site (and site access) secure, installing site cabins for the welfare of workers and undertaking initial site preparation. This may involve full or partial demolition of existing structures, decontamination of the site, installation of site drainage and the connection of services prior to the construction of the foundations. Scaffolding will be erected to suit the planned schedule of work to allow the safe movement of personnel and goods during the construction phase.

2.1  Site analysis A thorough site analysis is an essential first step that will assist development, design and construction decisions. The site analysis helps the: ❏❏ Client to assess whether the proposed project is viable (best done in consultation with

professional advisors)

❏❏ Client, designers, structural engineer and contractor to locate the best position for

❏❏ ❏❏ ❏❏ ❏❏

the building; this includes avoiding or accommodating identified problems where possible, while making the best possible use of physical features and environmental conditions Engineers to design the most suitable foundation system Mechanical and electrical consultants to design the service provision Designers and contractors to ensure that safe construction methods are used Environmental consultants to identify the most suitable way of dealing with any contaminants and problem materials  –  for example, remediation works, material reuse, on‐site treatment and disposal options to licensed tips

Barry’s Introduction to Construction of Buildings, Fourth Edition. Stephen Emmitt. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd. 17

18   Barry’s Introduction to Construction of Buildings

The site analysis comprises three interrelated research activities: the desktop study, the site reconnaissance and the ground (soil) investigations. The soil investigation may also involve laboratory tests on liquids and gases found in soil samples. The order in which these activities are carried out will depend to a large extent on the nature of the development and the timescales involved. Once information has been collected and analysed, it should be presented to the client as a final report, usually known as a performance appraisal. The ‘desktop’ study The ‘desktop’ study is a vital element in any site analysis exercise. The study involves the collection of all available documents and materials that can be obtained without having to visit the site. This includes information from local and national authorities, museums, private companies and published research reports. The client or previous owners of the land may also have relevant information to hand. Ground exploration and soil tests should not be undertaken before the desktop study is complete. This is because it is essential to know where services and potential hazards are located prior to carrying out any physical investigations. Analysis of documents may indicate that the site is unsuitable for development, or that special measures are required to overcome a particular challenge. The main types of information required are described in Table 2.1 and the following text. Ownership(s) and legal boundaries The client should provide, via a legal representative, information pertaining to the exact location of the site boundaries and responsibilities for maintaining them. These will need to be checked against a measured survey, and any areas of uncertainty checked by the legal representative. Other issues to be determined by the client’s legal representative include: Rights of way Rights of light Rights of support (for adjoining properties) Legal easements Ownership of land (essential where parcels of land are being assembled to make a larger site) ❏❏ Rights of tenants, etc. ❏❏ ❏❏ ❏❏ ❏❏ ❏❏

Ground conditions As a first step, it is usual to collect information on soil and subsoil conditions from the county and local authority. This includes knowledge from maps, geological surveys, aerial photography, and works for buildings and services adjacent to the site, which may provide a guide to subsoil conditions. Geological maps from the British Geological Survey; information from local geological societies; Ordnance Survey maps; and mining, river and coastal information may also be useful. Services All suppliers of services should be contacted to confirm the position of pipes and cables and the capacity of the existing supply. This includes gas, mains water, sewage and surface

Site Analysis, Set‐Up, Drainage and Scaffolding   19

Table 2.1  Typical sources of information • Maps: Detailed maps in different formats available from Ordnance Survey, Romsey Road, Southampton S016 4GU (http://www.ordnancesurvey.co.uk) • Historical maps: Online (e.g. http://www.old‐maps.co.uk) and libraries local to the site • Geological maps: Available from the British Geological Survey, the national repository for geosciences data in the UK; information provided: maps, records and materials, including borehole cores and specimens from across the UK; address: London Information Office, British Geological Survey, Earth Galleries, Natural History Museum, Exhibition Road, London SW7 2DE (http://www.bgs.ac.uk) • Hydrogeological maps: Soil reports and publication lists available from Soil Survey and Land Research Centre, Cranfield University, Silsoe, Bedford MK45 4DT • Meteorological information: Monthly and annual reports available on air temperature, wind speed, rainfall and sunshine; such information is useful when designing buildings and scheduling construction operations; statistics on averages and extremes also available; address: The Met Office, Room JG6, Johnson House, London Road, Bracknell, Berks RG12 2SY (http://www.metoffice.gov.uk) • Hydrological information: Surface water run‐off data available from water authorities, private water undertakings and local authorities • Site history: Available from previous owners and developers; site surveys and drawings used for previous development; records held by Building Control; local newspaper archives; and records held by the local planning authority • Location of gas mains: Gas suppliers • Location of electricity cables: Electricity suppliers • Mains electricity cables: Electricity‐generating boards • Water supply mains: Water suppliers • Main and local sewers: Local authority • Telephone and optical cables: Telecommunications authority • Railways: Rail authority • Canals: British Water Board • Mining activity: Coal Authority (http://www.coal.decc.gov.uk) • Aerial photographs: Many collections available of aerial photographs dating back over many decades; a directory of organisations and agencies that hold aerial photographs obtainable from Publications Department, Aslib, The Association for Information Management, Information House, 20–24 Old Street, London EC1V 9AP

drainage pipes, as well as electricity, broadband and telephone cables. It is usual for a representative of the supplier to visit the site to identify their equipment (which may be in a different physical location to that shown on plans). Contaminated land and methane Knowledge of previous land use, together with local authority records, can provide clues as to the likely contaminants to be found. Extensive soil testing should be carried out to ascertain the nature and extent of any contamination. Methane is largely associated with landfill sites, and local knowledge about the position of old tips/landfills may be informative. The most common contaminants include: ❏❏ ❏❏ ❏❏ ❏❏ ❏❏

Asbestos works Chemical or gas works Coal carbonisation plants and ancillary by‐products Industries making or using wood preservatives Landfill sites

20   Barry’s Introduction to Construction of Buildings

❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏

Waste disposals sites Metal works Munitions factories Nuclear installations Oil stores Paper printing works Railway land Scrapyards Sewage works Tanneries

Approved Document C also indicates the action necessary if any contaminants are discovered, as described in Table 2.2. Radon In certain areas of the UK, poses a threat to the inhabitants of buildings. Local authorities can provide advice on the likely level of contamination and regarding the protection required to prevent radon gas from entering buildings. Mining activity The UK has a long history of mining. Coal mining is the most common mining activity, and advice on mining records can be accessed via the Coal Authority. Some regions may have Table 2.2  Possible signs of contaminants and the relevant actions Signs of possible contaminants

Possible contaminant

Relevant action

No sign of vegetation, or poor or unnatural growth

Metals Metal compounds

None

No sign of vegetation, or poor or unnatural growth

Organic compounds Gases

Removal

Surface colour and contour of materials may be unusual, indicating waste

Metals Metal compounds Oily and tarry waste Asbestos (loose) Other mineral fibres Organic compounds including phenols Combustible material including coal and coke dust Refuse and waste

None

Flammable explosive and asphyxiating gases including methane and carbon dioxide Corrosive liquids Faecal animal and vegetable matter (biologically active)

Removal

Various

Remove in accordance with contaminated waste

Fumes and odours may indicate organic chemicals at very low concentrations

Drums and containers (whether full or empty)

Removal, filling or sealing Filling or sealing None Removal or filling Removal or filling Total removal or seek specialist advice

Removal, filling or sealing Removal or filling

Site Analysis, Set‐Up, Drainage and Scaffolding   21

different mining legacies, for example, salt mining in some areas of Cheshire and tin mining in Cornwall. The position of mines and mine shafts, as well as their size, depth and condition, may affect the positioning of buildings. Work to make old mine workings safe can add significant costs to the development, necessitating thorough research before finalising the site layout and commencing work on site. Flooding Heavy rainfall, buildings situated on or too close to flood plains and inadequate maintenance of rivers, watercourses and surface water drainage have all contributed to the flooding of properties. Enquiries should be made about previous incidents of flooding on or near the site, proximity to flood plains and any special requirements suggested or required by the various authorities and insurers to mitigate the risk of flooding. Site reconnaissance and surveys Written approvals from the client and/or the property owners must be in place, and a thorough risk assessment exercise must be carried out before entering the site, especially before any invasive investigations are carried out (which may require separate written permission). Obvious considerations are related to trespass and criminal damage, although the prime concern must be for the safety of those doing the investigations. Many sites will have been used previously, may still be in use and may contain buildings that are structurally unsound (which may be redundant or still in use, regardless of condition). Visual inspection of the site A visit to the site and its surroundings should always be made to record everything relevant to the proposed development. This will initially be undertaken by members of the design team, and then again at a later date by members of the construction team prior to construction. Site reconnaissance is often referred to as the ‘visual inspection’ or the ‘walkover’. From experience, we have found that two pairs of eyes (or more) are always better than one, and so the visual inspection should be undertaken by at least two, and preferably three, people – for example, the architect, engineer and contractor – with each taking his or her own notes but discussing features they come across. Careful observation should be made of the nature of the subsoil, vegetation, evidence of marshy ground, signs of groundwater and flooding, irregularities in topography, ground erosion, and ditches and flat ground near streams and rivers, where there may be soft alluvial soil. A record should be made of the foundations of old buildings on the site. Cracks and other signs of movement in adjacent buildings should be noted. When undertaking site reconnaissance on contaminated land, ensure as far as possible that all hazards have been identified and that correct safety procedures are followed. All maps and records should be consulted, so that any differences or omissions found when inspecting the site can be recorded. A visual inspection of physical site boundaries should be made and compared with legal documents that show boundaries. British Standard procedure for walkover surveys The British Standard for site investigations (BS 5930:1999) suggests that the surveyor should do the following when conducting a walkover survey: ❏❏ Traverse the whole area on foot (if possible and safe to do so) ❏❏ Establish the proposed location of work on plans

22   Barry’s Introduction to Construction of Buildings

Identify and record any differences on the plans and maps Record details of existing services, trees, structures, buildings and obstructions Check access and determine capability of sustaining heavy construction traffic Record water levels, fluctuations in levels, direction of flow and flow rate Identify adjacent property and the likelihood of it being affected by proposed works Identify any previous or current activities that may have led to contamination Record mine or quarry workings, old structures and other features Record obvious features that pose immediate hazard to public health and safety or the environment ❏❏ Record any areas of discoloured soil, evidence of gas production or underground combustion ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏

During a site reconnaissance, the following ground information and features should be noted (BS 5930:1999): ❏❏ Record surface features on site and on adjacent land, and note the following:

Type and variability of surface conditions. Compare land and topography with previous records; check for fill, erosions and cuttings. ◯◯ Any steps in the surface that may indicate geological faults. Steps in mining areas may be the result of subsidence. Other evidence of subsidence caused by mining may include compression or tensile damage to structures and roads, structures out of plumb and interference with the line of drainage patterns. ◯◯ Mounds and hummocks in relatively flat country often indicate former glacial conditions – for example, glacial gravel. ◯◯ Where the ground is terraced and broken on hill slopes, this may be due to landslips; small steps and inclined tree trunks may be evidence of creep and ground movement. ◯◯ Crater‐type holes in chalk or limestone usually indicate swallow holes that have been filled with soft material. ◯◯ Low‐lying flat areas in hill country may be the site of a previous lake and can indicate the presence of soft silts and peat. Record details of ground conditions in quarries and cuttings. Record groundwater levels (often different from the water levels of streams, ponds and lakes). Identify the position of wells and springs. Note the nature of vegetation in relation to soil type and wetness of soil. Unusual green patches, reeds, rushes, willow trees and poplars usually indicate wet ground conditions. Investigate structures in the vicinity of areas having a settlement history. ◯◯ ◯◯

❏❏ ❏❏ ❏❏ ❏❏

❏❏

Identification and physical location of services Before undertaking any digging, for example, for trail holes, it is necessary to clearly identify the nature of the services on the site and their actual position. Unfortunately, the majority of the plans provided by the service providers only give an approximate location of their pipes and cables; therefore, some detective work is required on site. The first task is to

Site Analysis, Set‐Up, Drainage and Scaffolding   23

identify all inspection covers and the nature of the service, and to compare their positions with those on the drawings. Handheld sonic and magnetic detecting devices to help locate the position of services are available from most plant hire firms. Exact position and depth can be established by carefully hand digging trial pits to expose pipes, cables and conduits. The service providers will also be keen to establish exact positions in an attempt to prevent damage to their pipes and cables. The organisations responsible for particular services should be invited to the site to help to establish the exact position, size and capacity of their supply and to resolve any uncertainty. In order to develop the site to its full potential, services may need to be re‐routed, if the appropriate authority will give permission. This is usually an expensive option, which can threaten the viability of the project. Alternatively, the proposed position of the building may need to be adjusted to enable the project to proceed without undue disruption to major service routes. Measured survey A land surveyor will conduct a topographical survey to establish the physical boundaries, existing features and variations in ground level. Most land surveyors have a standard list of features to be recorded during the land survey, although it is not uncommon to direct the land surveyors to particular areas of interest on or adjacent to the site. The measured survey will be provided as a digital file to import directly into computer‐aided design (CAD)/ building information modelling (BIM) software. Condition survey Condition surveys are used to record the physical condition of boundaries and adjoining property as well as the buildings on the site to be protected, refurbished or altered. This data helps to inform the design and construction team, in addition to forming a record, should any disputes arise or any claims for damage be made. The condition survey must be complete, and, where appropriate, approved by owners of properties adjacent to the site, before commencing any work that is likely to involve vibrations (e.g. demolition, excavations for foundations and basements, piling and the presence of heavy construction traffic). The condition survey is particularly valuable as a means of establishing how materials and buildings have weathered over time. Detailed drawings and written descriptions should be supported with photographic evidence, which must be identified with the date of the survey and the weather conditions at the time. Structural survey Structural surveys are used to record the structural condition of existing buildings. The need for a structural survey is usually established by analysing the results of the condition survey. However, in some situations, it may be obvious that a structural survey is required to establish the safety of the property before it is deemed safe (or not) to carry out the condition survey. Photographic and video surveys Photographic and video surveys are useful tools to prompt one’s memory when back in the office. Photographic surveys should be conducted in a systematic and thorough manner, with the position of the photographer and direction of view noted on a site plan.

24   Barry’s Introduction to Construction of Buildings

Soil investigations Details of the subsoil should include soil type, consistency or strength, soil structure, moisture conditions and the presence of roots. From the nature of the subsoil, the bearing capacity, seasonal volume changes and other possible ground movements may be assumed. To determine the nature of the subsoil below foundation level, it is necessary either to excavate trial pits some depth below the assumed foundation level or to bore in the base of the trial hole to withdraw samples. When proposing work to existing buildings (e.g. adding another floor), it will be necessary to expose the existing foundation in a number of places to check if it was built as detailed on drawings (if available), and also to check the subsoil below the foundation. The selection of the system will depend on economy, the proposed building works and the nature of the subsoil. Trial pits or boreholes should be sufficient in number to determine the nature of the subsoil over and around the site of the building and should be at most, say, 30 m apart. The common methods of obtaining samples include: trial pits, boreholes (cable percussive boreholes and rotary drilled boreholes), window sampling and dynamic probe testing. Trial pits To make an examination of the subsoil, trial pits and/or boreholes are excavated. Trial pits are usually excavated by a mechanical excavator, or in some cases by hand tools, to a depth of 3–4 m. The nature of the subsoil is determined by examination of the sides of the excavations. Soil and rocks can be examined in situ on the faces of the excavated pit, and samples taken for further laboratory tests. The trial pit also provides an indication of the ease of dig (or excavation), trench stability and groundwater conditions. For exploration of shallow depths (up to 3 m), this is usually more economical than boreholes. The pits are usually rectangular, being approximately 1.2 × 1.2 m in plan. The pits should be excavated in the vicinity of the proposed structure; if the pit is located under a proposed foundation, particular attention needs to be given to the material used to backfill the hole. In such situations, material should be of sufficient strength and well compacted. As each trial pit is excavated and inspected, a report should be made of the inspection. The typical information contained in the inspection – the trial pit log – is shown in Figure 2.1. Boreholes The term ‘borehole’ is often used in a generic sense to represent the various methods used to excavate and extract disturbed and undisturbed soil samples. All samples taken from boreholes should be sealed as soon as possible to minimise any loss of moisture before testing. Some of the most commonly used methods are discussed in the following text. Auger boring – rotary boring methods These holes are usually made by hand or powered auger into the ground. Auger holes are typically 75–150 mm in diameter. Short helical augers are used, and the disturbed samples of soil are collected as they are brought to the surface. Such methods are not widely used as they do not allow the soil to be examined in situ and are not capable of penetrating to the depth of boreholes. Rotary drilling is used where the boreholes are being cut into very dense gravel or bedrock. Samples or bedrocks are recovered in seamless plastic tubes, logged by an engineer and then taken for laboratory testing (Photograph 2.1).

Site Analysis, Set‐Up, Drainage and Scaffolding   25

Sketch of face of trial pit Location: Nicholls Farm – Leeds No 1. – Face A Date 08/6/2004 Coordinates 102.300 : 98.580 (Provided by developer) 0.00

0.50

Depth (m)

1.00

D1

1

D2

2

D3

3

Samples Sample type: Disturbed D1, Depth 0.00–0.25 D2, Depth 0.25–0.65 D3, Depth 0.65–1.25 D4, Depth 1.25–2.25 Note: chemical test results on soils are provided on document CTR/NF-L-1,8/6/2004

D4

1.50

4 2.00

D5 Trial pit completed 2.20 m

2.50

0.50

1.00

1.50

2.00

2.50

Width

Strata (1) (2) (3) (4)

Topsoil and grass 220 mm Made ground: firm to stiff orange brown sandy clay with a little gravel of limestone Made ground: soft to firm dark grey clay with occasional rootlets Medium dense dark grey clay

Notes: (1) (2) (3) (4)

Groundwater: no groundwater encountered Variability of faces: all faces were similar Stability of faces: all faces were stable Weather: overcast

Figure 2.1  Trial pit log.

Window samplers A window sampler is a steel tube of about 1 m length, with a hole cut into the wall of the tube, allowing the disturbed sample to be viewed or soil samples taken from the tube. The tube is driven into the ground using a lightweight percussion hammer and extracted with the aid of jacks. A range of tube diameters are available. In practice, the large tubes are driven in first and removed, leaving a hole for smaller tubes to be inserted and driven in further. Samples can be obtained down to a depth of 8 m.

26   Barry’s Introduction to Construction of Buildings

Photograph 2.1  Rotary drilling rig.

Window sampling can be carried out using either handheld pneumatic samplers or tracked percussive samplers. The samples are retrieved in seamless plastic tubes. A qualified engineer logs the samples (Photograph 2.2). Window sampling is suited to sites with restricted access and contaminated sites where ground disturbance should be minimal. Percussive samplers are also normally capable of performing penetrometer testing. Penetrometer testing is a continuous soil test procedure that enables the relative density or strength of the ground to be determined. Further information can be found at the Structural Soils web site (http://www.soils.co.uk). Percussion boring Boreholes are normally made using light percussion equipment. A weighted hollow tube of 150–200 mm diameter is dropped into the hole, so that the soil becomes lodged within the tube. The tube is then lifted to the surface and the sample removed. In clay soils, the method

Site Analysis, Set‐Up, Drainage and Scaffolding   27

Photograph 2.2  Soil samples ready for logging.

relies on the cohesive properties of the soil to hold it in the tube (clay cutter). In granular soils, a hollow tube with a flap over its base is used (shell or bailer). A single day’s drilling can excavate up to 15 m (typically 7–15 m). The materials that are collected during the drilling and excavation can be retained as disturbed samples; however, in cohesive soils, a tube of diameter 100 mm can be dropped to the bottom of the hole to collect an undisturbed sample (undisturbed sampling is generally confined to cohesive soils). The tube is then taken back to the laboratory for further tests. Standard penetration tests (SPTs) and vane tests can be carried out in the borehole as the drilling and excavation process proceeds. Photographic evidence from boreholes In very stiff clays and fissured rock, it is possible to take photographs of the strata using a remote‐controlled borehole camera. If it is clear that a borehole has entered a void, photographic evidence may determine the nature of the void – for example, mine shaft, sewer, cave, and so on. Exploratory investigation and foundation systems The information obtained from boreholes and trial pits will be used to design suitable foundation systems. Boreholes must penetrate through all unsuitable deposits such as unconsolidated fill, degradable material, peat, organic silts and very soft compressible clay. Once a suitable bearing stratum is reached, the depth of the borehole can be calculated. For low‐ rise buildings, the depth of the borehole can be calculated using the formulae discussed in the following text (BRE, 1995).

28   Barry’s Introduction to Construction of Buildings

Isolated pad or raft foundations Where the structure rests on an isolated pad or raft foundation (Figure 2.2), the following formula is used to calculate the depth of borehole required:



Borehole depth Depth of foundation 1.5 Breadth of foundation BHD D 1.5 B Closely spaced strip or pad foundations Where the structure rests on closely spaced strip or pad foundations (Figure 2.3), the following formula is used to calculate the depth of borehole required: Borehole depth Depth of foundation 1.5 2 (Space between foundations Breadth of foundation) BHD D 1.5 2S B

Structure on friction piles Where friction piles are used (Figure 2.4), the calculation is:



Borehole depth Depth of pile foundation 3 Breadth BHD D 3B BRE (1995) procedure for site investigations in low‐rise buildings suggests that boreholes should be drilled in straight lines to facilitate section drawings (Figure 2.5).

Borehole

Depth of foundation

Breadth of foundation

Borehole depth = Depth of foundation 1.5 Breadth of foundation BHD ≥ (D 1.5 B)

Figure 2.2  Depth of borehole for pad and raft foundations.

Site Analysis, Set‐Up, Drainage and Scaffolding   29

Space or distance between strip of pad footing S

D

Depth of foundation

B Borehole depth = Depth of foundation + 1.5 × (2 × Space between foundations + Breadth of foundation) BHD ≥ D + 1.5(2S + B) Used where S is less than 5 times B

Figure 2.3  Depth of borehole for closely spaced strip or pad foundations. Borehole

Depth Breadth

Borehole depth = Depth of pile foundation +3 × Breadth BHD ≥ (D + 3B)

Figure 2.4  Depth of borehole for friction piles.

Ground and soil tests There are a wide variety of on‐site and laboratory tests that can be used to establish the characteristic ground and soil conditions. The extent of soil investigation will be based on the nature of the building and characteristics of the site. More detailed site and laboratory studies will provide more information, reducing the risks inherent in building on unknown ground. Laboratory and on‐site tests that can be used include the following: On‐site test ❏❏ Plate load test ❏❏ Vane shear test

30   Barry’s Introduction to Construction of Buildings

A1 130

BH 5

140 130

120

BH 4

BH 4 BH 3

BH 3 Position of proposed building BH 2

BH 2

110 BH 1

110 100 90

100 Section A1–A1

Position of boreholes BH 1

120

90

A1 (a) Plan showing the position of boreholes

(b) Sectional drawing

Figure 2.5  Plan (a) and section (b) showing the position of boreholes.

❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏

California bearing ratio (CBR) test Dry density–moisture relationship SPT Lightweight dynamic penetrometers Cone penetration test (CPT) Methane/oxygen/carbon dioxide/barometric pressure test

Laboratory work ❏❏ ❏❏ ❏❏ ❏❏ ❏❏

Triaxial compression tests Liquid and plastic limit tests Sieve analysis – particle size and distribution Moisture content pH value tests

The soil tests will inform the foundation design, as discussed further in Chapter 3.

2.2  Site set‐up and security Site planning is essential to ensure the safe and efficient flow of work, especially for sites with limited space and/or those located in busy areas such as city centres. Although this is covered under the literature on construction management, a brief summary of the main issues to be considered is presented here, because it may influence decisions about how best to design and construct the building.

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Site set‐up Once the constructor has obtained legal possession of the site, it is possible to conduct preparatory work to make the site safe and accessible. Access During construction, safe access to the site is required for personnel, as well as for construction plant and delivery vehicles. Firefighting equipment must also have clear access in case of a fire or emergency occurring during the construction works. Temporary vehicular access may be allowed in consultation with the appropriate highways, police and town planning departments. Safe access for large cranes and wide, heavy and/or long loads will also need to be planned, especially in inner city areas where access may be restricted to certain times of the day. Storage and managing site waste Materials, equipment and machinery (plant) must be protected from the weather, accidental damage from site operations and theft. This applies equally to materials stored on site for short periods and those stored for longer periods. The need for temporary storage can be mitigated to some extent by the use of ‘just‐in‐time’ deliveries and the use of offsite construction. Space for the construction and subsequent protection from damage of sample panels is a related consideration. The reduction of waste on site is linked to good site management and good detailing. When detailing a building, attention should be given to reducing the amount of cutting and hence waste generated on the site (which is expensive to dispose of). Services and accommodation The wellbeing of construction workers and visitors to the site is an important factor to ­consider. Space must be provided for offices and comfort facilities. These are usually provided in specialist prefabricated site units that are hired by the contractor for the duration of the project. On highly constrained sites, these units are stacked vertically to save space. Access to services will also be required, including electricity (for heating and power), water and foul drainage. Security and safety Site security is required to protect materials and plant from theft and malicious damage, and to stop members of the public from inadvertently wandering on to the site and hence endangering their safety. Perimeter fencing must be secure, and all access points constantly monitored. In addition to fencing and physical barriers to unauthorised entry, many contractors also employ security firms to provide additional protection at night and on weekends. Monitoring of materials entering and leaving the site is also required to prevent pilfering. Legal requirements, tools and guidance on how to manage health, safety and welfare can be found on the Health and Safety Executive web site (http://www.hse.gov.uk). Statutory requirements All work must comply with the relevant building regulations, town planning consent (conditions may relate to the protection of trees and boundaries, archaeological digs, restricted

32   Barry’s Introduction to Construction of Buildings

working times, etc.) and other statutory requirements relating to construction works such as topical health and safety legislation (including the Construction Design and Management Regulations 2015). Contractors should also be working to the most appropriate guidelines, such as the Considerate Contractors scheme. House builders may also need to consult the most recent edition of NHBC Standards. Temporary weather protection Workers, building materials and building work will need to be protected from the vagaries of the weather. In the UK, the problem is usually associated with inclement weather and working in cold conditions during the winter. Materials delivered to site will require temporary weather protection until they are placed in the correct position. This may be for a few hours to several days, depending on how the work has been planned and executed. Similarly, work will need to be protected as it proceeds – for example, brickwork requires protection from rain and frost. Getting the building weathertight as quickly as possible is a major help to protecting workers from wind, rain and sun. Temporary weather protection over the entire building will provide protection to all work activities. This usually involves the erection of scaffold, which is then covered in sheeting to provide a weatherproof envelope. Although there may be a significant financial outlay for temporarily covering the entire building, it has the advantage of creating a more stable environment in which to work, resulting in quicker completion of work. This saves labour costs and reduces the risk of damage to materials and work from rain and wind. Cold weather working As a general rule, work should not proceed when the air temperature is below or likely to fall below 2°C. Frozen material must not be used. The temperature should be monitored and recorded at regular intervals. A maximum and minimum thermometer, sited in the shade, will indicate whether the temperature is falling or rising. Weather forecasting services, such as that provided by the Meteorological Office, can help in planning work over a slightly longer period. Work must be planned and adjusted to mitigate the effects of cold weather. Strong winds can reduce the temperature of mortar and concrete (and site personnel) more quickly as compared to still conditions. The wind chill factor must be considered in the planning of work. Similarly, topographical features such as hollows in the ground or sites overshadowed by high trees or buildings are likely to warm slower than sites that benefit from the sun’s rays. Covers must be placed over stored materials to protect them from frost, ice, rain and snow, and must be in place at the end of each working day. Covers should also be used to protect newly laid masonry and concrete. Portable heaters can be used to protect materials from frost damage during prolonged periods of cold weather. Concrete should not be placed in foundation trenches or oversite when the ground is frozen, because ground movement will damage the work when the temperature rises and the ground thaws. All formwork, reinforcement and other surfaces that come into contact with fresh concrete must be free of frost, ice and snow. Ready‐mixed concrete must be a minimum of 50°C when delivered (a requirement of BS 5328). Site‐mixed concrete should not be used if the air temperature is below 2°C. However, work can proceed if the aggregate temperature is above 2°C and free of frost and snow, the water for mixing is heated (but not

Site Analysis, Set‐Up, Drainage and Scaffolding   33

over 60°C), the cement is not heated, the ground is not frozen and the cast work can be protected against frost. At low temperatures, curing times will be extended, depending on the severity of the conditions, by up to 6 days. Masonry should not be laid when the temperature is below or is likely to fall below 2°C, unless heating is provided and the materials have not been damaged by frost or are frozen. New masonry must be protected against frost damage with covers and heating in severe weather. The use of admixtures such as plasticisers and accelerators should be used sparingly and always in accordance with manufacturers’ recommendations. Plasticisers provide improved frost resistance to mature mortar and concrete. Accelerators may help the mortar or concrete to set before the temperature falls below 2°C. Site preparation Turf, vegetable topsoil, plant roots and tree roots should be removed to a depth sufficient to prevent later growth and subsequent damage to the building. Vegetation contained in the soil will decay, which will create voids that may undermine foundations. Usually the vegetable top soil is moved to another site, or stored until required for landscaped areas. Levelling and setting out One of the first tasks to undertake is to establish the positions of the buildings and the various floor/datum levels. This requires careful surveying, measuring and checking against the measured survey drawings and design information. Building and grid lines should be set out, and, before any work can commence, a temporary benchmark should be established. Temporary benchmarks will provide a fixed level on the site for the duration of the works. All other levels for footings, floor levels, road levels, etc., can be determined by working out the difference in levels from the temporary benchmark. In order to establish the on‐site temporary benchmark, a fixed reference point close to the site needs to be found. Ordnance Survey benchmarks can often be found on churches, bridges and other large structures (and should be shown on the land surveyor’s drawings). This level can be transferred to temporary benchmarks placed on sturdy structures in positions where they are not liable to be knocked over or disturbed. The benchmark should be recorded on a site plan for reference during construction. Reference points on the ground also need to be established to allow workers to position the building and associated works correctly. North‐ and east‐based coordinates are used to position grid lines; these may be obtained using a global positioning system (GPS) or using two reference points with known coordinates. Alternatively, the building or grid lines can be set out off existing structures. Reduced‐level dig The existing ground must be taken down to workable levels. For simple housing developments on flat sites the ground floor level is usually positioned slightly higher than the existing ground level to reduce the need for deep excavation and to avoid problems with groundwater penetration. However, for most developments, it will be necessary to carry out a reduced‐level dig once the level has been established and grid lines or building lines have been marked out. Generally, areas of the site where major excavation will take place are

34   Barry’s Introduction to Construction of Buildings

reduced. The reduced‐level dig is excavated to the underside level of the floor construction; this is the largest volume of excavation that should take place. Reducing the level of the site where buildings are positioned helps to provide a level site for ease of work. Foundations that go deeper than the underside of the floor construction are excavated independently from this level. With careful planning, much of the material excavated can be repositioned on the site to avoid sending material to landfills.

2.3  Site drainage The term ‘surface water’ is used for rainwater and melted snow that falls onto the surface of the ground, including open ground such as fields, paved areas and roofs. Rainwater that falls on paved areas and roofs generally drains to surface water (storm water) drains, and then to soakaways or mains drainage. Paved areas are usually laid to a slight fall so that surface water drains to channels and gullies that are connected to surface water drains. Rainwater falling on natural open ground will in part lie on the surface of impermeable soils, evaporate to air, run off to streams and rivers, and soak into permeable soils as groundwater. The term ‘groundwater’ denotes water held in soils at and below the water table (which is the depth at which there is free water below the surface). The level of the water table will vary seasonally, being closest to the surface during rainy seasons and deeper during dry seasons when most evaporation to air occurs. In Approved Document C, there is a requirement for ‘adequate subsoil drainage’, to avoid passage of ground moisture to the inside of a building and to avoid damage to the fabric of the building. Subsoil drainage is also required where the water table can rise to within 0.25 m of the lowest floor, where the water table is high in dry weather and where the site of the building is surrounded by higher ground. Sustainable drainage system (SuDS) One of the impacts of urbanisation is the negative effect on rainwater catchment. Natural catchment would normally slow surface water run‐off by infiltration of water into the ground (recharging groundwater), and by uptake of water from vegetation before it reaches natural water courses. Once a site has been developed, the natural permeability of the ground is usually compromised, resulting in increased surface water run‐off (and reduced groundwater recharge) and reduced uptake by vegetation. Water run‐off reaches water courses much quicker, which may result in an increased risk of flooding and an increased risk of water pollution from the run‐off. The underlying principle behind SuDS is to better manage surface water and groundwater in a sustainable way. The idea is to try and mimic nature and manage rainfall close to where it falls. The aim is to: ❏❏ ❏❏ ❏❏ ❏❏ ❏❏

Reduce flood risk (quantity of water) Minimise water pollution (quality of water) Restore and maintain natural flow in water courses Improve water resources Enhance amenity and biodiversity

Site Analysis, Set‐Up, Drainage and Scaffolding   35

By following the SuDS guidance, it is possible to reduce the impact on natural water drainage. Simple measures can be taken, such as minimising the use of impermeable materials and including water features, such as ponds, to slow the rate of run‐off. Comprehensive guidance is available to designers, and local planning authorities will provide guidance on new development in an attempt to better manage surface water drainage. Surface water drainage To comply with SuDS, it is necessary to limit the amount of impermeable materials around buildings. Permeable materials that allow water to drain into the ground should be used for hard standing areas, such as patios, drives and pathways. In areas prone to flooding, there will be stringent measures in place that must be complied with as part of the town planning permission. External surfaces that are paved with impermeable materials, such as concrete, tarmac, paving slabs, bricks or granite sets, should be laid with slight slopes or falls to gullies or channels. They should also be laid to fall away from the external walls of buildings to prevent the possibility of water collecting at the base of a wall. The fall helps to discharge rainwater reasonably quickly for the convenience of people and to prevent the ponding of water, which would accelerate the deterioration of paving materials by saturation and the effect of frost on water lying in fissures in the material. A minimum fall of 1:60 is generally recommended for paved areas on flat ground. To economise in drain runs, paved areas should drain in two or more directions to yard gullies, with drainage channels between gullies in large paved areas to effect further economies. The drainage of the paved area in Figure 2.6 is arranged in a way known as each way falls, which drain to gullies. In areas prone to flooding, it may be necessary to discharge the water into an underground holding tank or to a pond to reduce the rate of surface water run‐off and hence reduce the quantity of water entering water courses. Channels Channels between gullies may be level and depend on natural run‐off, or may be laid to a slight fall by a gentle sinking towards a gully. A small square area of paving may be laid to fall to one central gully, with channels formed from each corner to the gully by the intersection of slopes. Forming this slope at intersections of falls, termed a ‘current’, Fall of land

Gully Channel Paved area Channel Gully

Figure 2.6  Paved area drainage.

36   Barry’s Introduction to Construction of Buildings

may involve oblique cutting of paving slabs or bricks to provide a level surface. Yard or surface water gullies are set on a concrete bed to finish just below the paved surface. The gullies generally have a 100‐mm square inlet and are either trapped with a water seal when they discharge to combined drains or are untrapped for discharge to a separate storm water drain. Figure 2.7 shows a trapped clay yard gully with loose cast iron grating for access to clear blockages. The graph in Figure 2.8 indicates the area of paving that can be drained relative to the estimated flow and size of the drain and to the gradient or fall. Square grating

To

dra

in

Figure 2.7  Clay yard gully.

9000

120 110 300 mm diam.

7000

100 90

6000

80

5000

70

225 mm diam.

60

4000

50

3000

40 150 mm diam.

2000 1000 0

Litres per second

Area drained in m2 (assuming 50 mm/h rainfall)

8000

30 20

100 mm diam.

10 50

100

150

200

0 250

Gradient 1 in . . .

Figure 2.8  Graph for determining the diameter and gradient of surface water drains.

Site Analysis, Set‐Up, Drainage and Scaffolding   37

Drainage systems With separate drainage systems, roof and surface water drainage will connect to a separate system of underground drains discharging to the mains sewer. For the rain and surface water drains, it will generally be satisfactory to have a system of either clay or uPVC drains with rodding eye access fittings. An inspection chamber will be required near to the boundary of the property. The description of pipe laying, bedding and gradient for foul water drains will apply equally to roof and surface water drains for which untrapped gullies are used. Soakaways A ‘soakaway’ is a pit into which roof and surface water is drained and from which the water slowly seeps into the surrounding ground (Figure 2.9). Soakaways are used where a combined sewer may not be capable of taking additional water and/or where the surface water sewer is too far from the property. It can also be used as an alternative means of discharge. Outside the more densely built‐up urban areas, there is often an adequate area of land surrounding the building to use soakaways. If the soil is waterlogged and the water table or

Concrete cover slab Drain inlet

Simple pit dug in firm pervious ground such as chalk Pit filled with hardcore or clean broken stone in clay Pit lined with dry stone or brick in granular soil

Porous lining to permit water to percolate through Precast concrete drum with lower rings perforated

Figure 2.9 Soakaways.

38   Barry’s Introduction to Construction of Buildings

natural level of subsoil water is near the surface, it is pointless to construct a soakaway. In this situation, the surface water will have to be discharged by pipe to the nearest sewer, stream, river or pond. Soakaways should be positioned at least 3 m away from buildings, so that soakaway water does not affect building foundations, and they should also be on slopes down from buildings rather than towards buildings, to avoid overflowing and flooding. Subsoil drains Subsoil drains are used to improve the run‐off of surface water and the drainage of groundwater to maintain the water table at some depth below the surface to: ❏❏ ❏❏ ❏❏ ❏❏

Improve the stability of the ground Avoid surface flooding Alleviate or avoid dampness in basements Reduce humidity in the immediate vicinity of buildings

Subsoil drains may be designed to be either open jointed or jointed, porous or perforated. The materials used in the manufacture of the pipes are clayware, concrete or plastics. The pipes are laid in trenches to follow the fall of the ground, generally with branch drains discharging to a ditch, stream or drain. On impervious subsoils, such as clay, it may be necessary to form a system of drains to improve the run‐off of surface water and drain subsoil to prevent flooding. Some of the drain systems used are natural, herringbone, grid, fan and moat or cut‐off. Natural system The natural system, which is commonly used for field drains, uses the natural contours of the ground to improve run‐off of surface groundwater to spine drains in natural valleys that fall towards ditches or streams. The drains are laid in irregular patterns to follow the natural contours, as illustrated in Figure 2.10a. Herringbone system The herringbone system, illustrated in Figure 2.10b, features fairly regular runs of drains connected to spine drains that connect to a ditch or main drain. This system is suited to shallow, mainly one‐way, slopes that fall naturally towards a ditch or main drain and can be laid to a reasonably regular pattern to provide a broad area of drainage.

Main drain laid in natural valley Branch drain laid down natural slope (a) Natural system of drains

Branch drains

Main drain laid down slope to ditch stream or drain (b) Herringbone system of drains

Figure 2.10  (a) Natural system; (b) herringbone system.

Site Analysis, Set‐Up, Drainage and Scaffolding   39

Grid system The grid system is an alternative to the herringbone system for draining one‐way slopes where branch drains are fed by short branches that fall towards a ditch or main drain, as illustrated in Figure 2.11a. This system may be preferred to the herringbone system, where the run‐off is moderate, because there are fewer drain connections that may become blocked. Fan system A fan‐shaped layout of short branches, illustrated in Figure 2.11b, drains to spine drains that fan towards a soakaway, ditch or drain on narrow sites. A similar system is also used to drain the partially purified outflow from a septic tank to an area of subsoil where further purification of the water will take place. On sloping building sites on impervious soil where an existing system of land drains is already laid and where a new system is laid to prevent flooding, a moat or cut‐off system is used around the new building to isolate it from general land drains, as illustrated in Figure 2.12. The moat or cut‐off system of drains is laid some distance from and around the new building to drain the ground between it and the new building, and to carry water from the diverted land drains down the slope of the site. The moat drains should be clear of paved areas around the house.

Branch drain

Branch drain

Main drain to ditch stream or drain (a) Grid system of drains

Main drain to ditch stream or drain (b) Fan-shaped system of drains

Figure 2.11  (a) Grid system; (b) fan system.

Land drains connect here

Drains laid around building

Drains to soakaway, ditch stream or drain

Figure 2.12  Moat or cut‐off system.

40   Barry’s Introduction to Construction of Buildings

Laying drains Groundwater (land) drains are laid in trenches at depths between 0.6 and 0.9 m in heavy soils and 0.9–1.2 m in light soils. The nominal bore of the pipes is usually 75 or 100 mm for main drains and 65 or 75 mm for branches. The drainpipes are laid in the bed of the trench and surrounded with coarse gravel (without any fine gravel). A filtering material (traditionally, this was inverted turf or straw) is then placed on top of the gravel; this allows the water to percolate through to the drain without allowing fine material to pass through and block up the surrounding gravel. Excavated material is backfilled into the drain trench up to the natural ground level. The drain trench bottom may be shaped to take and contain the pipe or finished with a flatbed, as illustrated in Figure  2.13, depending on the nature of the subsoil and the convenience of using a shaping tool. Where drains are laid mainly to collect surface water, the trenches are filled with clinker, gravel or broken rubble to drain water either to a drain or without a drain, as illustrated in Figure 2.14, in a model known as the ‘French drain’. The system used will depend on the anticipated volume of water and the economy of dispensing with drainpipes.

Excavated material backfilled

Cohesive soil Clinker, gravel or rubble

Inverted turf or straw Land drain

Clinker, gravel or rubble

Trench shaped for pipe

Figure 2.13  Land drains.

Trench filled with clinker, gravel or rubble

(a) Surface water drain

Figure 2.14  (a) Surface water drain; (b) French drain.

Trench filled with clinker, gravel or rubble

(b) French drain

Site Analysis, Set‐Up, Drainage and Scaffolding   41

2.4  Foul drainage The primary function of a foul drainage system is to facilitate the transfer of foul water and matter quickly, economically and safely from a building to the mains drainage or collecting vessel. The foul drainage system may be constructed once the building is set out and before the foundations are constructed, in parallel with the construction of foundations or after the foundations are complete. Scheduling will depend on the characteristics of the site and the availability of plant and machinery. Drainage layout The layout of foul drains depends on whether foul water and rainwater are discharged to a common drain system (combined) or to separate drain systems (Figure 2.15), which in turn depends on whether there is one sewer or separate sewers for carrying foul and rainwater. Foul drainage systems should be kept simple. Fittings that discharge foul water should be grouped together on each floor to economise on pipe runs; discharge pipe branches should run to a common waste stack; and groups of fittings on each floor should be positioned one over the other to minimise pipework. Rainwater pipes from roof gutters and gullies to collect water from paved areas should also be positioned to simplify drain runs. Wherever practicable, changes of direction and gradient should be limited to minimise the number of access points. Because the drains for foul water and rainwater will generally run across each other at some point, it is necessary to adjust the level or gradient (slope) of the drains to accommodate this. A combined drainage system must be ventilated throughout to conduct foul air discharge to the open air. In this system, it is necessary to fit trapped gullies with a water seal. With separate systems of foul and rainwater drains, it is necessary to fit trapped gullies

Interceptor manhole Combined drain system

Se

we

r

Separate drain system

Se

we

r

Figure 2.15  Combined and separate drain systems.

42   Barry’s Introduction to Construction of Buildings

only to the discharge of foul water fittings, where the discharge pipe does not serve as a ventilation pipe. Foul water drainage systems should be ventilated by a flow of air, with a ventilating pipe to the head of each main drain and any branch drain that is more than 6 m long serving a single appliance or 12 m long serving a group of appliances. Ventilated discharge pipes such as discharge stacks, discharging directly to the drain, are commonly used for ventilation of drains. Drain runs should be laid in straight lines wherever possible to encourage the free flow of discharge water by gravity, with gentle curves in drain runs only where straight runs are not practicable. Bends in drain runs should be limited to positions close to or inside inspection chambers and to the foot of discharge pipes, and should have as large a radius as practicable. Where drain runs are near to or under a building, precautions should be taken to accommodate the effects of settlement without damage to the drain. Drainpipes Drainpipes are classified as either rigid or flexible. Rigid pipes are those that fail by brittle fracture before they suffer appreciable deformation, and these include clay, concrete, cement and cast iron pipes. Flexible pipes are those that suffer appreciable deformation before they fracture, and these include uPVC. The deformation of flexible and rigid pipes is controlled by the use of a granular bed, and limitations of load by the design of the trench and its backfilling. Clay pipes Clay pipes are mass‐produced in highly automated plants. The selected clays are ground to a fine powder, and water is added for moulding. Simple fittings are formed by extrusion, and the parts of junctions are extruded and then cut and joined by hand. The moulded clay pipes and fittings are then dried in kilns to encourage uniform loss of water, to avoid loss of shape, and then fired in continuous tunnel kilns. Pipes and fittings that are to be glazed have a ceramic glaze or slip sprayed on, or they are dipped in the slip before they enter the kiln. The nominal bore (inside diameter) of clay pipes for drains is 75–900 mm – in increments of 25 mm for bores of 75–250 mm, then one 50 mm increment to 300 mm, followed by increments of 75 mm for bores of 300–900 mm, as illustrated in Figure 2.16. A wide range of fittings is made for clay drains such as bends, junctions, channels and gullies, some of which are shown in Figure 2.17. The advantage of using clay pipes for drains is that the comparatively short length of the pipes and the wide range of fittings are adaptable both to the straightforward and the more complex drain layouts, and the pipes themselves are inert to all normal effluents. Jointing Flexible joints should be used with rigid clay drainpipes, so that the drain lines can accommodate earth movements under, around or over the pipeline, within the joint. Flexible joints can be made in all weather conditions and, once made and tested, the trench can be backfilled to protect the pipeline from damage. There are two types of flexible joints in use: the socket joint for socket and spigot pipes, and the sleeve joint for plain‐ended clay pipes. Typical joints are shown in Figures 2.18 and 2.19. These flexible joint seals are made from

Site Analysis, Set‐Up, Drainage and Scaffolding   43

Available lengths: 0.3 and 0.6 for 75 mm, and 0.3, 0.6, 0.9, 1.0, 1.2 and 1.5 m for 100–900 mm

Effective length

Socket

Spigot

Socket end of pipe with grooves on the inside surface Bore of pipe Pipe barrel Spigot end of pipe with grooves on the outside surface

Figure 2.16  Clay drainpipes.

Figure 2.17  Clay drainpipe fittings.

44   Barry’s Introduction to Construction of Buildings

Sealing action achieved by rubber gasket O ring located in the groove in the spigot

Plastic fairings cast round inside of socket and outside of spigot

Figure 2.18  Section at junction of socket and spigot clay pipes. Polypropylene flexible sleeve

Rubber sealing rings Lead-in bevels on plain-ended pipes

Figure 2.19  Section at junction of plain‐ended clay pipes showing flexible coupling.

natural rubber, chloroprene rubber, butyl rubber or styrene–butadiene rubber. The flexible socket joint is made with plastic fairings cast on the spigot and socket ends of the pipe to provide a simple push‐fit joint. It suffers the disadvantages that the joint may be damaged in handling, and the cut pipe lengths may present difficulties on site. The flexible coupling joint is made with a close‐fitting, flexible, plastic sleeve with rubber sealing rings. The ends of the plain‐ended pipes are bevelled to assist in forcing pipe ends into the sleeve to make a close, watertight seal. Concrete pipes Spun concrete pipes are often used for major infrastructure works. The normal diameter of pipes ranges from 300 mm to 1.8 m. The standard pipe is usually around 2.5 m long, and a pipe of 6000 mm diameter weighs approximately 1200 kg. Concrete pipes need to be lifted and manoeuvred into position using mechanical plants. Most concrete pipes come fitted

Site Analysis, Set‐Up, Drainage and Scaffolding   45

with gaskets, and, once lubricant has been applied to the barrel, it can be pushed into the socket for a watertight seal. Cast iron pipes Cast iron pipes are used for drains because of their superior strength where there is unstable or made up ground, in shallow trenches, under buildings, for drains suspended under floors of buildings, in heavily waterlogged ground and where sewage is under pressure from pumping. Cast iron and ductile iron pipes are made with socket and spigot ends or with plain ends. All pipes are hot dip coated with either a bituminous or tar coating inside and out. Pipes are manufactured with bores of 75, 100, 150, and 225 mm and in lengths of 1.83, 2.74, and 3.66 m, together with a wide range of fittings. Jointing A flexible push‐fit joint is used for cast iron and ductile iron pipes. A rubber gasket, fitted inside the socket of pipes, comprises a heel of hardened rubber that aligns the pipes, and a bulb of softer rubber that makes the joint, as shown in Figure 2.20. The pipe ends must be clean, and are lubricated and joined by leverage from a crowbar for small pipes, or a fork tool for larger pipes. The joint is flexible and will accommodate longitudinal and axial movements. The joint is rapidly made in any conditions of weather, the pipeline may be tested immediately and the trench can be backfilled to protect the pipeline. uPVC pipes uPVC pipe is extensively used because of its ease of handling, cutting and jointing, as well as the low cost. The pipe is light in weight and flexible as it can, to some extent, deform under load without fracture. Deformation should be limited to an increase in horizontal diameter of not more than 5% to avoid blockages in pipelines or breaks to joints. Pipe sizes are described for the outside diameter of the pipe as 110, 160, and 200 mm, and lengths are 1.0, 3.0, and 6.0 mm (Figure 2.21). Because of the comparatively long lengths in which this pipe material is made, with consequently few joints necessary, the material lends itself to assembly at the ground level, from where it can be lowered into narrow trenches. Heel of hardened rubber Soft bulb of gasket

Chamfered ends to spigot Retaining bead on inside of socket

Figure 2.20  Flexible push‐fit joint for cast iron.

46   Barry’s Introduction to Construction of Buildings Obtainable in 1, 3 and 6 m

Effective length Nominal sizes outside diameter 110, 160 and 200 mm

Socket Spigot

Pipes are manufactured with plain ends also

Figure 2.21  PVC drainpipes.

Section Socket of pipe with moulding to accept ring seal

O ring slid over spigot of pipe

Figure 2.22  PVC socket and spigot push‐fit joint.

Jointing Socket and spigot push‐fit joints with rubber rings depend on a shaped socket end of pipe, as shown in Figure 2.22, or a shaped coupling designed to fit around rubber sealing rings that fit between the socket or coupling and spigot end to make a watertight seal. Because the rubber ring seal has to be a tight fit between the pipes, it requires careful manipulation to fit the spigot end into the socket end of the pipe or coupling while making certain the rubber seal takes up the correct position in the joint. Because of the considerable thermal expansion and contraction of this material, it is necessary to provide for movement along the pipe

Site Analysis, Set‐Up, Drainage and Scaffolding   47

lengths through the allowance between the spigot end of pipes and the shoulder on the socket end of the pipe or coupling, as illustrated in Figure 2.22. Several proprietary systems of push‐fit joints are available. Sleeve joints of polypropylene with rubber sealing rings to plain‐ended pipes depend on a separate plastic coupling sleeve that fits over the spigot ends of plain pipe lengths. Rubber seal rings in the ends of the sleeve compress on the spigot ends of the pipes being joined, as illustrated in Figure 2.23. To provide a tight fit between the coupling sleeve and the pipe ends, it is necessary to apply some force to push the pipe ends into the sleeve, for which cramps or jacks are available. The ends of the pipes being joined fit to shoulders in the sleeve to provide the expansion allowance illustrated in Figure 2.23. Sleeve jointing is generally favoured over the socket and spigot joint. Solvent‐welded joints (Figure 2.24) are available for short lengths of drainpipe. This type of joint is not used for long lengths of drain, as the rigid joint makes no allowance for expansion. The joint is made by bringing together the spigot and socket ends of the pipe after they have been brushed with a PVC solution and methyl chloride. The solvent dissolves the PVC, which fuses together after some time, but takes a while to harden fully. Polypropylene sleeve

Expansion allowance Locked in rubber seal ring

Figure 2.23  PVC sleeve joint. Pipe ends carefully cleaned before jointing

Excess solvent wiped off Welded joint achieved by bringing together spigot and socket of pipes which have been brushed at the ends with solvent (PVC solution and methyl chloride)

Figure 2.24  PVC solvent–welded joint.

48   Barry’s Introduction to Construction of Buildings

Drainpipes made of uPVC are commonly used with proprietary drain systems, which comprise a package of plastic connections, clearing eyes and access bowls for inspection, to combine economy and speed of assembly and laying. Because of the comparatively extensive range of fittings manufactured in clay, it is not uncommon for clay gullies, for example, to be used in conjunction with uPVC pipes. Drain laying Drains laid underground should be of sufficient diameter to carry the anticipated flow, and should be laid to a regular fall or gradient to carry the foul water and its content to the outfall. Pipe gradient or fall Research into the flow load of drains in use has shown that the size of the drainpipe and its gradient should be related to the anticipated flow rate in litres per second, so that the discharge entering a drain will determine the necessary size and gradient of the drain. For short drain runs, the invert level at the top and bottom of the run can be pegged out at the correct level, and either sight lines or string lines used to plot the gradient of the pipe. Pipe lasers are more commonly used today. The laser sits at one end of the pipe run and the target is positioned in the end of the pipe being levelled. When the laser strikes the centre of the target, the pipe is at the correct level (Photograph 2.3). Drains are designed to collect and discharge foul water and rainwater by the flow of water under gravity. Drains are, therefore, laid to a regular fall (slope) towards the sewer or outflow. The necessary least gradient or fall of a drain depends on the anticipated flow of water through it and the necessary size of drain to carry that flow. Table  2.3 gives the recommended minimum gradients for foul drains. Approved Document H1 recommends that a drain carrying only wastewater should have a diameter of at least 75 mm, and a drain carrying soilwater at least 100 mm. The term ‘wastewater’ is generally used to include the discharge from baths, basins and sinks, and soilwater includes the discharge from water closets. Figure 2.25, from Approved Document H1, shows the relationship of flow rate to gradient for three pipe sizes with drains running three quarters of proportional depth. The rate of flow in drains with gradients as flat as 1:200 is given. Drains are not commonly run with gradients below 1:80 because the degree of accuracy necessary in setting out and laying drains required for shallow falls is beyond the skills of most building contractors. Drains should be laid at a depth sufficient to provide cover for their protection, and the excavation should be as narrow as practical for bedding and laying the drain lines. The greater the width of the trenches at the crown of the pipe, the greater the surcharge loads on the pipe. It is advantageous, therefore, to bed the drain in a narrow trench, which may be increased in width above the level of the crown of the drain for ease of working. With modern excavating machinery, flexible joint pipelines may be assembled above the ground, and then lowered into and bedded in comparatively narrow trenches, thereby saving labour and cost in excavation, improving health and safety, and providing the best conditions for the least loads on the pipeline. The depth of the cover to drainpipes depends on the depth at which connections are made to the drain, the gradient at which the pipes are laid and ground levels. Depth of

Pipe laser

(a) Laser set up in manhole. Once set at the correct gradient, pipes can be laid to the correct level

(b) The laser can be used to obtain a level for the pipe bedding; the drainage is placed onto the bedding and positioned to correct fall

Laser target Concrete bed Channels

(c) Once the pipe is correctly positioned, the pipe bedding covers the whole pipe

(d) Channels laid on the bed of concrete, ready to form a new manhole

Photograph 2.3  Laying drains.

Table 2.3  Recommended minimum gradients for foul drains Peak flow (L/s)

Pipe size (mm)

Minimum gradient (1:…)

Maximum capacity (L/s)

75 100 75 100 150

1:40 1:40 1:80 1:80* 1:150†

4.1 9.2 2.8 6.0 15.0

1

*Minimum of one water closet. †Minimum of five water closets.

50   Barry’s Introduction to Construction of Buildings

30

150

Flow rate (L/s)

20

10 8 7 6 5 4

10

mm

0m

75

3

m

mm

dia

me

dia

me

dia

2

1:10

1:20 1:30

ter

1:50 1:70 1:100

ter

me

ter

1:200

Gradient (1 in)

Figure 2.25  Discharge capacities of foul drains running 0.75 proportional depth.

Table 2.4  Limits of cover for standard‐strength rigid pipes in any width of trench

Pipe bore 100

150

Fields and gardens

Light‐traffic roads

Heavy‐traffic roads

Bedding class

Min

Max

Min

Max

Min

Max

D or N F B D or N F B

0.4 0.3 0.3 0.6 0.6 0.6

4.2 5.8 7.4 2.7 3.9 5.0

0.7 0.5 0.4 1.1 0.7 0.6

4.1 5.8 7.4 2.5 3.8 5.0

0.7 0.5 0.4 – 0.7 0.6

3.7 5.5 7.2 – 3.3 4.6

cover is taken as the level of finished ground or paving above the top of a drainpipe. A minimum depth of cover is necessary to provide protection to the pipe against damage, and a maximum depth to avoid damage to the drain by the weight of the backfilling of the drain trenches. Minimum and maximum cover for rigid pipes is set out in Table 2.4. Flexible pipes should have a minimum of 0.6 m of cover under fields and gardens, and 0.9 m under roads. Bedding flexible pipes Flexible pipes should be laid in a narrow trench, on granular material such as clean, natural aggregate. This granular material is spread in the base of a trench that has been excavated and roughly levelled to the gradient or fall of the drains. The granular material is spread and finished to a thickness of 100 mm. Lengths of drainpipe are then lowered into the trench and set in position by scooping out the granular bed from under the collars of pipe ends, to

Site Analysis, Set‐Up, Drainage and Scaffolding   51

Main backfill

Selected fill

200 min

Selected or granular fill

Granular bedding min 100 thick

100 min

Granular side fill up to crown of pipe

Figure 2.26  Bedding for flexible pipes.

set the pipeline in place at the centre of the trench. Further granular material is then spread and lightly packed on each side of the pipeline, to support it against deformation under load, as illustrated in Figure 2.26. A layer of granular material or selected fill, taken from the excavated material, is then spread over the pipeline to a depth of 100 mm. A further layer of selected fill, free from stones, lumps of clay or other material larger than 40 mm, is spread in the trench to a thickness of 200 mm. The trench is then backfilled with excavated material up to the ground level, and consolidated. This drain‐laying operation requires care and some skill to bed the drain line correctly, and further care in backfilling to avoid disturbing the drain. Where the bed of the trench is narrow, it may be necessary to cut the sides of the trench above the level of the bed of the drain, in a ‘V’ shape, sloping out from the centre for ease of access. Bedding rigid pipes Where a drain trench is excavated in cohesive soil such as clay for laying rigid pipelines of clayware, for example, it is possible to lay the pipes directly on the trench bottom that has been finished to the required pipe gradient by hand trimming using shovels. The pipe lengths are lowered into the trench, and soil from the trench bottom is scooped out under each socket end of the pipe, so that the barrel of the pipes bears on the trench bottom and the collars keep the drain line in place. For this operation to be successful, the trench needs to be sufficiently wide for a worker to stand in it astraddle the pipeline to scoop soil out from below the pipe collars. Once the pipeline is in place, a cover of selected fill from the

52   Barry’s Introduction to Construction of Buildings

excavation, free from large stones or lumps of clay, is spread in the trench to a depth of 150 mm above the crown of the pipes, and the trench is backfilled to the surface level. This bedding system is suited to the use of socket and spigot, and clay pipes with one of the flexible joints that can be used in all weather conditions. When the bed of drain trenches cannot be trimmed to the pipe gradient, a bed of granular material is spread in the bed of the trench and levelled to the pipe gradient to a thickness of 100 mm, as illustrated in Figure 2.27. The rigid pipes are lowered into the trench, and a layer of selected fill is carefully spread around the pipes and then filled to a level of 150 mm above the crown of the pipes. The trench is then backfilled to the surface level. This type of bedding is suited to plain clay pipes joined with flexible sleeves. As an alternative, the granular bedding is spread 100 mm thick in the bed of the trench, the pipes are lowered into the trench and granular bedding is scooped out under the collar ends of pipes. The granular material is then spread around the pipes, up to half the outside diameter of the pipe, as shown in Figure 2.28. The selected fill is then spread in the trench to a depth of 150 mm above the crown of the pipes, and the trench is backfilled to the surface. This system of bedding has the advantage that the granular bedding on each side of the pipes maintains them in position as the trench is filled. It may well be that the most economical depth of flexible drainpipes below the surface will provide less depth of cover than recommended. To avoid unnecessary excavation, it is acceptable to lay flexible pipes with less cover when they are laid under fields or gardens. The pipes are laid on a bed of granular material 100 mm thick in the bed of the trench and then surrounded and covered with granular material up to a level of 75 mm above the crown of the pipes, as illustrated in Figure  2.29. Concrete paving slabs are then laid over the granular material, bearing on

Main backfill

Selected fill 150 mm

Granular bedding min 100 mm thick

Lowest edge of a socket to be at least 50 mm above trench bottom

Figure 2.27  Bedding for rigid pipes: granular bedding – Class N.

Site Analysis, Set‐Up, Drainage and Scaffolding   53

Main backfill

Selected fill 150 mm

Granular bedding min 100 mm thick

Granular side fill up to half outside diameter of pipe

Figure 2.28  Bedding for rigid pipes: granular bedding – Class B.

Granular fill surround Concrete paving slabs Main backfill

Minimum 75 mm granular fill Drain pipe Granular bedding

Figure 2.29  Protection for flexible pipes under fields and gardens.

54   Barry’s Introduction to Construction of Buildings

offsets in the trench walls. The trench is then backfilled to the surface level with selected fill from the excavation. The concrete slabs, the granular material bed and the surround of the pipes will provide adequate protection against deformation of the pipes. Rigid drainpipes laid at a depth that provides less than the recommended cover below the surface should be provided with protection from damage by an encasement of concrete, with flexible movement joints at each socket or sleeve joint of the pipeline. The drain trench is filled with concrete, to a depth of 100 mm, in sections along the length of the trench equal to the pipe length. Between each section, a 13‐mm‐thick compressible board, holed for pipes, is set to the width of the trench. Before the concrete is hard, it is scooped out for the socket ends of the pipe against one side of the board. A pipe is set in position up to the board, and the next section of concrete is laid up to another flexible board in the trench. The concrete is scooped out for the next pipe, which is pushed into the flexible joint of the first pipe, and so on along the length of the trench. Once the drain line is laid, it is tested, and then concrete encasement is spread around the pipes, between the flexible boards, to provide a cover of 100 mm all round the drain. The trench is then backfilled to the surface. Drains under buildings and walls When a drain is laid under a building and the crown of the pipes is at all points 300 mm or more below the underside of the ground floor slab, the drains should have flexible joints and be surrounded by granular material at least 100 mm thick all around the pipes. Where the crown of the drain is within 300 mm of the underside of the ground floor slab, it should be encased in concrete as an integral part of the slab. There is a possibility that slight settlement of a wall might fracture the drain where it is laid to run through the wall under a building. There are two methods of avoiding the possibility of damage. The first method is to provide a minimum 50 mm clearance between the wall and the drain. The wall is built with a small lintel over the opening in the wall through which the pipe is to run, to provide at least 50 mm of clearance all round the drain. Where the drain is laid to run through the wall, two rigid sheets, holed for the pipe, are fitted to the pipe and secured in place by screws and plugs to the wall, as illustrated in Figure 2.30, to exclude vermin or fill. The disadvantage of this system is that it is difficult to provide a close fit of a rigid board to a pipe, and to make a watertight joint between the external board and the wall using brickwork. The other method of providing protection to a drain run through a wall is to provide for any slight settlement of the wall by means of rocker pipes. A short length of pipe is built into the wall, projecting no more than 150 mm on each side of the wall. A length of pipe, at most 600 mm long, is connected to each end of the built‐in pipe and connected to it with flexible joints. These rocker pipes are likewise connected to the drain line with flexible joints, so

Opening in wall

Lintel

Rigid sheet

Figure 2.30  Drainpipe through an opening in the wall.

Site Analysis, Set‐Up, Drainage and Scaffolding   55

that any slight movement of the pipe built into the wall is accommodated by the flexible joints of the rocker pipes. This system, illustrated in Figure 2.31, is best executed with plain clay pipes and flexible sleeve joints. Drains close to buildings On narrow building sites where there is only a narrow strip of land on each side of a building, it may be necessary to run a drain parallel to a flank wall of the building. To provide the necessary gradient or fall, the drain may be at or below the level of the wall foundation. To avoid the possibility of the loads on the wall foundation imposing undue pressure on the drain, it may be necessary to provide additional protection. Where the drain trench bottom is less than 1 m from the foundation, the distance indicated by the letter ‘A’ in Figure 2.32, the drain should be laid on a bed of concrete and then covered with concrete up to the level of the underside of the wall foundation. A drain laid 1 m or more from the wall foundation, the distance indicated by ‘A’ in Figure 2.33, and appreciably below Short length of pipe built into wall Rocker pipe

Flexible joints Rocker pipe

600 max 150 max

600 max 150 max

Figure 2.31  Drainpipe built into the wall.

A Concrete

Figure 2.32  Drains less than 1 m from foundations.

A

A less 150 mm Concrete bed and surround to drain

Figure 2.33  Drains 1 m or more from foundations.

56   Barry’s Introduction to Construction of Buildings

the foundation of the adjacent wall, should be bedded on concrete and then covered with concrete up to a level equal to the distance from the wall of ‘A’ minus 150 mm. This additional protection, which is expensive, may not be wholly satisfactory, as it provides a rigid encasement that makes no allowance for possible differential settlement along the length of the drain run, which might fracture the encasement and pipe run. Access points to drains There should be adequate access points to drains to provide means of clearing blockages by rodding through drains. Rodding is the operation of pushing flexible, sectional rods (that can be screwed together) down drain lines to clear blockages. The three types of access points in use are: ❏❏ Rodding eyes, which are capped extensions of drainpipes ❏❏ Access fittings, which are small chambers within, or extensions of, drainpipes ❏❏ Inspection chambers, which are large chambers with an open channel; small inspection

chambers have no working space at drain level; large inspection chambers (sometimes called ‘manholes’) do provide working space at drain level

Access points should be provided on long drain runs and at or near the head of each drain run, at a bend or change of gradient, a change of pipe size and at junctions where each drain run to the junction cannot be cleared from an access point. The limits of the depth and minimum dimensions for access points are set out in Table 2.5, and the minimum spacing of access points in Table 2.6. Inspection chamber An inspection chamber is usually constructed as a brick‐lined pit at the junction of drain branches and at changes of direction and gradient, to facilitate inspection, testing and clearing obstructions. An inspection chamber is formed on a 150‐mm concrete bed on which Table 2.5  Minimum dimensions for access fittings and chambers Internal sizes Type Rodding eye Access fitting Small Large Inspection chamber Manhole

Shaft

Cover sizes

Depth to invert (m)

Length × width (mm × mm)

Circular (mm)

Length × width (mm × mm)

Circular (mm)

– − 0.6 or less

As drain but min. 100 150 × 100

− 150

– 150 × 100

– 150

225 × 100 – 450 × 450 1200 × 750 1200 × 750 1200 × 840 900 × 840

– 190* 450 1050 1200 1200 900

225 × 100 – 450 × 450 600 × 600 600 × 600 600 × 600 600 × 600

– 190* 450† 600 600 600 600

0.6 or less 1.0 or less 1.5 or less over 1.5 over 2.7 over 2.7

*Drains up to 150 mm. †For clayware or plastics may be reduced to 430 mm in order to provide support for cover and frame.

Site Analysis, Set‐Up, Drainage and Scaffolding   57

Table 2.6  Maximum spacing of access points (in metres) Access fitting From

To

Start of external drain* Rodding eye Access fitting Small (150 mm diameter) 150 × 100 mm Inspection chamber Manhole

Small

Large

Junction

Inspection chamber

Manhole

12 22

12 22

– 22

22 45

45 45

– – 22 22

– – 45 45

12 22 22 45

22 45 45 45

22 45 45 90

*Connection from ground floor appliances or stack.

Cast iron frame and cover

Soil vent pipe

225-mm thick brickwork Concrete cover slab Direction of flow

Branch bend

Benching

Section 225-mm brickwork

Concrete base

Plan From yard gulley

Figure 2.34  Cut‐away sectional view of inspection chamber.

brick walls are raised. In the bed of the chamber, a half‐round channel or invert takes the discharge from the branch drains, as illustrated in Figure 2.34. The walls of the chamber may be of dense engineering bricks. If less dense bricks are used, the chamber is lined with cement rendering to facilitate cleaning, and sometimes the outside wall of the chamber is rendered to prevent the infiltration of groundwater. The chamber is completed with a cast iron cover and frame (Photograph 2.4). The word ‘invert’ is used to describe the lowest level of the inside of a channel in an inspection chamber, or the lowest point of the inside of a drainpipe, and measurements to the invert of a drain are used to determine the gradient of that drain (Figure 2.35). In the bed of the chamber, the three‐quarter section branch drains discharge over the channel in

58   Barry’s Introduction to Construction of Buildings

English bond Stoppers inserted ready for air test

Benching to the sides of the inspection chamber (a) Brick inspection chamber – English bond Inspection chamber shores and trench sheets Channel cut in existing pipe

(b) Channels and benching in inspection chamber

Trench box

Adjustable box

(c) Deep inspection chamber: existing pipe run exposed and ready to form a new Inspection chamber

(d) Temporary ground support used to allow safe laying of drain and formation of inspection chamber

Photograph 2.4  Laying inspection chambers.

Soffit Bore size of pipe

Invert

Invert

(a) Pipe

(b) Half-round channel

Figure 2.35  Section through drainage showing the invert level.

Site Analysis, Set‐Up, Drainage and Scaffolding   59

the direction of flow, and fine concrete and cement rendering (termed ‘benching’) is formed around the branches to encourage flow in the direction of the fall of the drain, as shown in Figure 2.34. Backdrop inspection chamber Where a branch drain is to be connected to a main drain or a sewer at a lower level, it is often economical to construct a backdrop inspection chamber to avoid the deep excavation of a drain line. The backdrop chamber is constructed of brick on a concrete bed, and the higher branch drain is connected to a vertical or drop drain that discharges to the channel in the backdrop chamber, as illustrated in Figure 2.36 (the near side and end walls are omitted for clarity). The drop drain is run in cast iron drains, supported by brackets screwed to plugs in the wall. Access bowl drain system Where uPVC drains are used for small buildings such as houses, a system of PVC access bowls or chambers may be used. The hemispherical access bowl (Figure 2.37) is supplied Galvanised malleable step-irons built into courses of brickwork to simplify access into deep drop inspection chamber; galvanised malleable to be used in inspection chambers over 4.5 m in depth

Access bend Cast iron pipework drop inside manhole

Open channel to permit inspection and clearance of blockages Concrete base Concrete benching finished with steel-floated cement mortar

Figure 2.36  Backdrop inspection chamber.

Direction of flow

60   Barry’s Introduction to Construction of Buildings

Branch inlet

Branch inlet

Hemispherical access bowl with drain hole in the lowest position for outlet connector Cast iron frame and cover

Concrete casing min thickness 100 mm PVC outlet connector Outlet

Section through access pit

Figure 2.37  Mascar access bowl drain system.

with one hole for the outlet drain, and up to five additional holes can be cut on site to suit inlet branches. Purpose‐made inlet and outlet PVC connectors are provided for solvent welding to the bowl for outlet and inlet connections to drains. One access bowl is sited close to the building for the discharge from the soil pipe and ground floor foul water and wastewater fittings. The access bowl is extended to the ground level with PVC cylindrical extension sections, one of which is illustrated in Figure 2.37. The access bowl is set on a concrete bed, and, after the drain runs have been connected, it is surrounded with a minimum of 100 mm of concrete for protection and stability. A cast iron frame and cover is set on top of the access bowl at the ground level. These access bowls may be used at changes of direction in drain lines and at the site boundary, before the connection to the sewer, for the purposes of rodding to clear blockages and inspection of flow. Rodding point drain system This sealed underground drain system combines the advantages of the long lengths of pipe and the simplicity of jointing uPVC drain lines, with rodding points and one or more inspection chambers for access for inspection, testing and clearing blockages. Figure 2.38 shows a typical layout. The rodding points are used as a continuation of straight drain runs extended to the ground level with an access cap. It is possible to rod through each drain run

Site Analysis, Set‐Up, Drainage and Scaffolding   61

Rodding point access cap

Precast concrete sectional inspection chamber

Adjustable bends

Adjustable bend Access cap

110-mm uPVC pipe Adjustable bend 110-mm uPVC drain

Branch from WC Branch from RWP

Adjustable bends

To sewer

135° branch

Rodding eye RWP

Rodding eye Stack

RWP

Rodding point access cap 110-mm uPVC drain

RWP WC RWP Rodding eye To sewer Key plan to drain layout

Figure 2.38  Rodding point drain system. RWP, rain water pipe.

to clear a blockage, and this arrangement dispenses with the need for inspection chambers at all junctions and bends, with appreciable savings in cost. Soil stack pipe to connection drains In the single‐stack system, a single pipe serves to carry both soilwater and wastewater discharges directly down to the drains, so that the soil pipe or stack may serve as a ventilation stack pipe to the drains. In this system, the water trap seals to each of the sanitary appliances serve as a barrier to drain smells entering the building. At the base of the soil pipe is a large radius or easy sweep bend to facilitate clearing blockages. Whether the soil pipe is run inside or outside the building, there should be a large radius bend at its connection to an inspection chamber. Where the drain connection to a soil or waste pipe passes through the wall of the building, there should be at least 50 mm of clearance all around the drain to allow for any settlement of the wall that might otherwise fracture the pipe if it were built into the wall. The opening in the wall around the pipe is supported by small lintels or brick arches and covered with rigid sheet on both sides, as illustrated in Figure 2.39.

62   Barry’s Introduction to Construction of Buildings

100-mm discharge stack

Cavity wall

Arch or lintel Sheet to keep opening clear

50-mm clearance

100-mm drain branch

921/2° large radius bend

Figure 2.39 

Soil stack connection to the drain.

Rainwater down pipe Back inlet trapped gulley Grating GL

To drain

Figure 2.40  Trapped gully.

Gullies Where there is a combined sewer that takes soil and wastewater discharges and rainwater from roofs and paved areas, it is necessary to use a trapped gully at the foot of rainwater downpipes, so that the water seal in the gully serves as a barrier to foul gases rising from the drains. The trapped gully illustrated in Figure 2.40 has a back inlet connection for the rainwater pipe and a grating that serves as an access to clear blockages and to take water running off paved areas. These gullies are made with either back or side inlet connections for rainwater pipes. Where there are separate drain and sewer systems for foul water and rain and surface water, the gullies that collect rainwater and surface water can be connected directly to the surface or storm water drain. The fitting (Figure 2.41) is described as a rainwater ‘shoe’ to

Site Analysis, Set‐Up, Drainage and Scaffolding   63

Rainwater down pipe

Grating To storm water drain A raising piece can be inserted into tray to suit ground level

Figure 2.41  Rainwater shoe.

differentiate it from a gully that has a water seal. The shoe has a grating that fits loosely into a tray to provide access. As there is less likelihood of blockages in surface water drains as compared to soilwater drains, it is not considered necessary to form inspection chambers at all junctions, bends and changes of gradient to the drain, as is the case with foul water drains. Rodding eyes at salient points to facilitate clearing drains are generally considered adequate for the purpose. Because of the wide range of fittings available, it is common to use clayware gullies and rainwater shoes for most drainpipe materials. Gullies and shoes are usually bedded on a small concrete base to provide a solid base for connection to stack pipes and drains. Private sewers, common drain There is no exact distinction between the words ‘drain’ and ‘sewer’, but the most generally accepted definitions are that pipelines under privately owned land, laid and maintained by the owner, are called drains, and pipelines laid and maintained by the local authority under roads are called sewers. A private sewer, also termed a ‘combined drain’, is a system of drains laid for the use of two or more buildings, paid for and maintained by the owners of the buildings and making one connection to the public sewers. A common drain or sewer to a terrace of houses such as that illustrated in Figure 2.42 requires one drain connection to the public sewer. Where properties do not directly front onto public roads and sewers, as shown in Figure 2.43, it is convenient to lay a private sewer (sometimes called a ‘combined drain’). This allows a connection from each house to the private sewer and only one connection to the public sewer. With this type of drainage layout, it is necessary to apportion the cost of maintenance and repair for the private sewer to the properties connecting to it. Connections to sewers Connections to public sewers are generally made by the local authority or the building owner’s contractor under the supervision of the local authority. In both cases, the connection is paid for by the building owner. In new developments, a branch connection is constructed in a new sewer, which is then connected to an existing sewer.

64   Barry’s Introduction to Construction of Buildings

Inspection chambers or rodding points

Terraced housing

Combined drain collects discharge from each house Road Sewer Combined drain discharges to sewer

Figure 2.42  Common drain.

Access bowls connect to combined drain that discharges to sewer

Road Sewer

Figure 2.43  Combined drains (private sewers).

Drain testing All newly laid drain lines should be tested for watertightness after jointing and laying, and again after backfilling and consolidation of trenches. Existing drains may also need to be tested prior to and after building works to existing buildings. The methods available are discussed in the following text. Water test The drain is tested by water pressure, applied by stopping the low end of the drain and filling it with water to a minimum head of water, as illustrated in Figure 2.44. The head of water should be 1.5 m above the crown of the high end of the pipeline under test. Where long drain lines are to be tested, and the head of water would exceed 6 m due to the length and gradient of the drain, it is necessary to test in two or more sections along the line. The loss of water over a period of 30 minutes should be measured by adding water from a measuring vessel at regular intervals of 10 minutes, and noting the quantity required to maintain

1.5 m above crown of drain

Site Analysis, Set‐Up, Drainage and Scaffolding   65

Bend with rubber ring fitted at top of drain

Aluminium pipe to provide head of water

Drain plug Drain filled with water

Figure 2.44  Water test.

the original water level. The average quantity added should not exceed 1 litre per hour per linear metre, per metre of nominal internal diameter. The water test is a test of watertightness under pressure, a condition that a freely flowing drain will never suffer, and is thus a test of watertightness far more rigorous than the drain line is designed for. Air test The air test is generally accepted as less rigorous test than the water test. The drain line is stoppered at both ends, and air pressure is provided by a pump, the pressure being measured by a graduated U‐tube or manometer. Expanding drain stoppers – suited to take the tube from the pump at one end of the drain line, and the tube to the pressure gauge or manometer at the other – are fitted to the ends of the drain line to be tested. Air pressure is applied to the drain through a hand‐ or foot‐operated pump until a pressure of 100 mmHg is recorded on the graduated U‐section pressure gauge, and the valve to the gauge is shut. An initial period of 5 minutes is allowed for temperature stabilisation, and the pressure is then adjusted to 100 mmHg. The pressure recorded by the U‐gauge or manometer should then not fall below 75 mm over a further 5 minutes for a satisfactory test. Where trapped gullies and ground floor appliances are connected to the drain line being tested, a pressure of 50 mmHg is adopted as the measure. Smoke test The smoke test has been used for old drains where the water or the air test is too rigorous. The drain is stoppered at suitable intervals and smoke is introduced under pressure from a smoke capsule or smoke machine. The purpose of the test is to discover leaks by the escape of smoke, which will find its way to the surface through a considerable depth of soil and all but the most dense concrete. The reason for using a smoke test, particularly on old drains, is to give some indication of the whereabouts of likely leaks before any excavation to expose drains is undertaken. This may be of use on long runs of drain and where drains run under buildings. The appearance and smell of smoke may give a useful indication as to where the excavation to expose drains should take place. Water, air and smoke tests act on the whole of the internal surface of drains. These tests may indicate leaks due to cracks in the crown of the drain. As drains never run full bore, a crack in the crown of a drain may not cause any significant leakage and may not warrant repair.

66   Barry’s Introduction to Construction of Buildings

Closed‐Circuit Television (CCT) surveys Modern technology provides a means of conducting a visual inspection of the inside of drain runs by the use of a small digital camera that is inserted into and run down the line of a drain to provide a digital record of the condition of the inside of the drain. This data can be used to obtain an estimation of the extent of work required and help to establish the position of excavation. Sewage collection and treatment In rural areas where connection to a main sewer is not possible, it will be necessary to use a cesspool, septic tank or sewage treatment plant. It is necessary to make sure that the installation conforms to current pollution prevention requirements and is appropriate for the intended purpose. Advice is available from local authority environmental control officers. Cesspool A cesspool is an underground chamber or container used to collect and store all foul and wastewater from buildings. Cesspools are emptied by pumping the contents out to a tanker, and are used where there is no ready access to a sewer and where ground is waterlogged or the slope of the site does not allow the use of a more compact and convenient septic tank. The traditional cesspool was a brick‐lined pit, with engineering brick walls 220 mm thick, lined inside with cement and sand rendering, set on a concrete base. A reinforced concrete cover over the cesspool would be formed at, or just above, ground level, with some form of access cover for emptying and a fresh air inlet (FAI). A range of prefabricated cesspools is available today. These are made from glass‐reinforced fibre plastic (GRP) in the form of sealed containers with capacities of 7500–54 000 litres. Larger capacities of up to 240 000 litres can be made. The ribbed cylindrical cesspool, with access point, inlet and FAI, is delivered ready to lower into an excavated pit with the cylinder lying on its long axis. The cesspool is laid on a bed of concrete and surrounded with a lean mix of concrete, with the cover to the access point at or just above the ground level. Septic tank A septic tank is designed to take the outflow of soil and wastewater, retain some solid organic matter for partial purification and discharge the liquid sewage through a system of land drains to the surrounding ground to complete the process of purification. The usual capacity of septic tanks is from 2800–6000 litres, equating to the waste produced by approximately 4–22 people. A range of moulded, high‐grade‐polyethylene, bulb‐shaped tanks is available, with access turret, inflow and outflow connections and an FAI (Figure 2.45). The tank is bedded on concrete and surrounded with lean mix concrete with the access cover at or just above ground level. The septic tank is divided into three chambers. The outflow of the foul and wastewater drains is discharged to the lower chamber (A in Figure 2.45), in which the larger solid particles of sewage settle to the bottom. As more sewage flows down the inlet, liquid rises through the slots in the bell‐shaped division over the lower chamber and enters the middle chamber (B). In this chamber, fine particles of solid matter settle on top of the bell‐shaped division and settle through the slots into the lower chamber. As the tank fills, the liquid, now comparatively free of solid sewage matter, rises through the slots in the inverted bell‐shaped division to the third and upper chamber (C).

Site Analysis, Set‐Up, Drainage and Scaffolding   67

Floating ball

FAI

Inlet

Outlet

C B

A

Figure 2.45  Prefabricated septic tank.

As this upper chamber fills, the now partially purified liquid rises through the outflow to a system of perforated land drains. The land or leaching drains, laid in trenches surrounded by granular material, spread the liquid sewage over an area sufficiently large to encourage further purification of the liquid sewage by aeration and the action of microorganisms in sewage. The accumulated sludge of solid sewage that settles in the base of the tank should be removed into a tanker at intervals of not more than 12 months. A hose from the tanker first empties the upper chamber, by suction. As the liquid level falls, the ball that seals the division between the upper and ­middle chambers falls away. This provides access to remove the sludge from the lower chamber. Sewage treatment plant The preferred and more expensive system for sewage outflow, where no sewer is readily available, is the installation of a sewage treatment plant that will produce a purified liquid outflow that can be discharged to nearby ditches and streams without causing pollution of water supplies. A form of sedimentation tank, similar to a septic tank, causes solid sewage to settle. The resultant liquid outflow is further purified by exposure to air to accelerate the natural effect of microorganisms, native to sewage, combining with oxygen to purify the sewage. The three systems used to speed up the exposure of the liquid sewage to air are: (1) By spreading over a filter bed (2) By spreading over rotating discs (3) By pumping in air to combine with the liquid (aeration) A range of prefabricated treatments is available from specialist suppliers for this purpose.

68   Barry’s Introduction to Construction of Buildings

Natural systems It may be feasible to discharge the foul water to specially designed and constructed reed beds (ponds), which naturally filter the waste. This method is suited to sites with plenty of space in which to construct the reed beds. Advice should be sought from the appropriate local authority and specialists at an early design stage to ensure that there is no pollution of natural water courses.

2.5 Scaffolding Scaffolding is a temporary structure that is designed to provide a safe and level working area above the ground level. Scaffolding is used on new‐build projects and for work to existing structures, including maintenance and repair work. This temporary structure needs to be structurally safe, yet also capable of rapid erection, disassembly and reuse. Scaffold may be owned and maintained by a contractor, although it is more common for the scaffolding to be hired from a scaffolding subcontractor as and when required. Temporary structures must be designed and inspected by a competent person (e.g. certified structural engineer). It must be erected, altered and dismantled in accordance with guidance from the National Access & Scaffolding Confederation (NASC) and the relevant standards – for example, BS 5973: 1993 Access and Working Scaffolds and Special Scaffold Structures in Steel. Further information can be found on the Health and Safety Executive web site, including guidance on inspection and maintenance. The structure must be checked on a regular basis and immediately following extreme weather to ensure it remains safe to use. Scaffold components Scaffold is usually constructed from aluminium or steel tubes and clips, with timber or metal scaffold planks used to form a secure and level working platform. Access between levels is by timber or metal ladders, secured to the scaffold. The configuration of the tubes, clips and ties is discussed and illustrated further under the different types of scaffold systems. Some components, such as scaffold boards and edge protection, are common to all scaffold systems. Scaffold boards A standard timber scaffold board is made from sawn softwood, the span determined by its thickness, as shown in Table 2.7. The most common size is 225 mm wide by 38 mm thick. Lightweight metal scaffold boards are used in some systems. The boards must be closely Table 2.7  Scaffold board thickness and span Thickness of scaffold board (mm) 32 38 50 63

Maximum span between bearers (ledgers) (mm)

Minimum overhang from bearer (mm)

Maximum overhang (mm)

1000 1500 2600 3200

50 50 50 50

128 152 200 252

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Hop-up scaffolding brackets for two/three boards can be used to increase the width of the working platform. Should only be used to gain access; materials must not be stored on the platform Note: Care must be taken when using ‘hop-up’ brackets to avoid inducing secondary bending into standards

Gaps between the working platform and the building should be kept as small as possible, but must not exceed 300 mm

Figure 2.46  Hop‐up brackets.

butted together, so that there is no chance of them slipping off the supporting tubes. Each board must overhang the ledger by 50 mm, but the overhang must not exceed four times the thickness of each scaffolding board. Scaffolding boards are butted together to make a working platform; the minimum working platform depth is three boards. When materials are loaded onto the platform, the clear passage for workers should be at least 430 mm, and a minimum clear width of 600 mm must be maintained at all times to allow for the manoeuvring materials. When laying bricks, the scaffold platform should be at least five boards wide (1150 mm). Hop‐up brackets may be used to increase the working height of the lift and to increase the working width of the scaffolding platform (Figure 2.46). When using hop‐up brackets, care must be taken not to overload the scaffold. The cantilevered bracket induces bending moments in the standards. Toe boards Toe boards must be used at the end of the scaffolding to ensure that materials and tools do not fall off the scaffold. The toe boards must be a minimum height of 150 mm. The boards also prevent the possibility of people slipping off the edge of the platform. Toe boards may be removed to allow access for materials and workers, but must be replaced immediately afterwards.

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Sheeting and netting preventing objects and equipment from falling off the scaffolding Toe board clip holds toe board securely in position Close boarding, tightly butted preventing objects from falling

Adequate lighting and signage to alert and warn of the hazard Protective padding prevents injury from collision Netting and safety fencing preventing access under the scaffold. Where access is allowed under the scaffold, the walkway should be fully boarded, protecting from falling objects

Figure 2.47  Independent scaffolding with safety signs, lights and hazard warning.

Safety for pedestrians When scaffolding is positioned in areas accessed by pedestrians, it is necessary to use high‐ visibility warning tape and lighting. Lagging and padding can be placed around the standards to reduce the risk of injury from accidental impact with the scaffold (see Figure 2.47). Close boarding, netting and sheeting must be used to prevent objects from falling onto anyone below. While the scaffolding is being erected, it will be necessary to use a physical barrier to protect the area and to provide appropriate signage at access points to warn against unauthorised access. Scaffold types Putlog scaffolds Putlog scaffolds are erected as the external wall is constructed. The scaffolding uses the external wall as part of the support system (Figure 2.48 and Photograph 2.5). Standards and ledgers are tied to the putlogs. Each putlog has one flat end that rests on the bed or perpendicular joints in the brick or blockwork. The blade end of the putlog is usually placed horizontally and inserted fully into the brickwork joint, ensuring a full bearing is achieved. Where putlog scaffolds are used on refurbishment work, joints may be raked out to insert the blade end. In such works, the blade may also be placed vertically. Where the putlog scaffold is used in new works, the putlog is placed on the wall at the required lift height, and

Site Analysis, Set‐Up, Drainage and Scaffolding   71

-

Figure 2.48  Putlog scaffold.

-

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Ledger

Sway bracing

Putlogs built into wall

Standards

Scaffold base plate

Scaffold board sole plate

Photograph 2.5  Putlog scaffolding.

the wall is constructed around the blade end of the putlog. While the system uses less scaffolding and is less expensive than independent scaffolding, it is essential that the erection of the scaffold be coordinated with the sequencing of brickwork. Zigzag (sway) bracing is applied diagonally to the face of the scaffold, tying the ledgers and standards together. Plan bracing and ledger bracing should be used where specified. Independent scaffolding These scaffolds are erected ‘independently’ of the building structure, and are tied to the structure through window openings (Figure 2.49 and Photographs 2.6 and 2.7). Ties are required to ensure horizontal stability is maintained. Independent scaffolds are constructed from two parallel rows of standards tied by transoms, which bridge the width of the scaffold, and ledgers, which run along the length of the scaffold. A space is usually maintained between the scaffold and the building to allow the masonry to progress unhindered by the scaffold. The gap allows the brickwork to be checked for plumb, and also helps to reduce damage to the brickwork caused by mortar snots splashing off the scaffold and onto the

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Max gap between working platform and building 300 mm Inner board Boarded platform comprises defect free scaffold boards, 225 × 38 × 3900 mm

Guard rail

Intermediate guard rail Mesh guard prevents materials falling from platform Toe board clip holds toe board securely in position Double coupler

Ledgers Coupler

Diagonal façade bracing Plan bracing used above 8m Transom Ledger Ledger brace or cross brace (alternate bays) Standard Inner standard

Base plate Sole plate 38 × 225 mm Note: Sway bracing is also required across the face of the scaffold to stabilise the outside row of standards. Independent scaffolds have to be tied to the building to provide lateral and longitudinal stability. Tying needs to be enhanced if the scaffold is debris netted or sheeted

Figure 2.49  Independent tied scaffold.

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Standard

Double coupler Ledger brace

Transom Ledger

Innerstandard

Photograph 2.6  Independent scaffold

wall. On long stretches of scaffold, continuous diagonal tubes can be used to run from the top to the bottom of the scaffold structure. These act as façade bracing. Bracing is used to resist horizontal loads and to stiffen the structure, preventing distortion to the rectangular grids. Sway (zigzag) bracing may be applied diagonally to the face of the scaffold, tying the ledgers and standards together. Lateral bracing is also applied across the ledgers. Proprietary scaffold systems Proprietary systems are another type of independent scaffold. Proprietary systems rely on the same principles as independent scaffold but use standard lengths for ledgers, transoms and standards, all of which are capable of being clipped together and dismantled easily and quickly (Figures 2.50 and 2.51). The standards often come with spigot ends, which allow the next standard to be located over the locating spigot very quickly. The jointing systems vary depending on the manufacturer. Proprietary systems rely on ledgers and transoms having a locating lug or bracket fixed to each end; these ends can be quickly dropped into the clips, sockets or cups, which are fixed at regular intervals on the standards (Figure  2.51 and Photograph 2.8a and b). Components, such as ledgers and transoms, are designed so that they can be interchanged.

Site Analysis, Set‐Up, Drainage and Scaffolding   75

Handrail

Intermediate guard rail Mesh guard prevents materials falling from platform Toe board clip holds toe board securely in positioned

(a) Guard rail and toe board

(b) Double coupler

Diagonal façade bracing (sway bracing)

Transom or putlog Ledger

Standard Base plate Timber sole plate

(c) Standard base plate

(d) Scaffold clip

Photograph 2.7  Scaffolding components.

For small scaffolds, bracing may not be required across the width of the scaffold since the frame is very rigid. Bracing must, however, run across the bays in accordance with the manufacturer’s instructions. Where loads are increased or hop‐ups are used, additional bracing is required. Each proprietary system varies with manufacturer and system, and the manufacturer’s instructions must be carefully followed to ensure that the scaffold is erected safely. To aid the flow of work, ‘hop‐up’ scaffolding units can be used to increase the height that the workforce can access at each lift (Figure 2.50). These can be used between the standards or between the internal standard and wall, providing a platform that is closer to the area of work and not reducing the width of the standard platform.

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Hop-up brackets for two/ three boards

Spigot locating tube for the next lift of standards Steel standards Intermediate guard rail (made from interchangeable transom) Connecting brackets every 500 mm Toe board clip holds toe board securely in position Scaffold boards span between 1.2 and 1.5 m Transom

500 mm

300 mm maximum

System scaffolds are very rigid and may not require bracing at low heights across the width. Bracing is required across bays Bracing is required if the load capacity is increased or hop-ups are used.

Jack Base plate Timber sole plate 38 × 225 m Note: System scaffolds need to be tied to the building façade to ensure stability

Figure 2.50  Proprietary scaffolding system – based on the SGB CUPLOK system.

Proprietary scaffolds have the benefit of rapid erection and disassembly; however, their use is limited to relatively standard operations due to the size of the components. Where loads are known to be considerable and the scaffolding arrangement is complicated due to specific project layout/geometry, traditional scaffolding designed by a structural engineer may provide a more flexible and appropriate solution. Lateral stability – tying into the building Independent, putlog and proprietary scaffold systems must be tied into stable parts of the building structure to ensure that the scaffolding remains stable. Ties must not be linked to fittings and fixings such as balustrades or service pipes. Ties can be locked behind the walls of window openings, between floors or braced against the cill and head of window openings (Figures 2.52, 2.53, 2.54 and Photographs 2.9, 2.10). Loads are transferred at the tie points, and the structure must be capable of supporting the load.

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System connections for standard ledgers and transoms

As the bevelled cup is rotated it locks against lugs which are welded to the standards

Steel standards

Transom

The upper cup slides over the ledger and transom location ends. The upper cup is rotated by tapping the lugs with a hammer

Ledgers and transoms are lowered into the bottom cup

Ledger

Bottom cup is welded to the standard

Figure 2.51  System method of connecting standards, ledgers and transoms – based on the SGB CUPLOK system.

(a)

(b)

Photograph 2.8  (a) Proprietary connection for standards, ledgers and transoms. (b) Standards with adjusting jack and base plate.

The scaffold design must always be checked to ensure that it is capable of carrying the load of the scaffold, as well as the loads imposed by materials, the workforce and the wind. Additional ties may be required if the loads exerted on the scaffolding are increased. Where protective sheeting is used (discussed later), extra ties will be needed to transfer the wind loads.

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close to building prevents the scaffold moving inwards

Protective cap protects the building from damage Through tie could be positioned horizontally or vertically

Packing or resilient pad

Double coupler

Timber protection to cavity and reveal Scaffold board or timber packing protects masonry and holds tie firmly in place

Transom Ledger Standards

Figure 2.52  Scaffold through tie.

Ties can, and often do, obstruct work. For example, it may not be possible to fit windows where a through tie is fitted. Before any ties are removed, the scaffold design must be checked to ensure that it will remain stable while the tie is temporarily removed or repositioned. Weather protection – scaffold sheetings Protective sheeting is tied to the scaffold structure to provide some protection to the workers and the building works from wind and rain. The sheeting may also help to protect the public from dust and debris falling from the scaffolding as work proceeds. Protective sheeting is usually made from polythene sheets, although other materials such as timber panels, corrugated steel sheeting and natural fabrics may be used. It is common practice to use the external face of the weather protection for advertising. The protective sheeting will be subject to wind load, increasing the wind loading on the scaffold considerably. Thus, scaffolding must be designed to ensure that the wind loads can be accommodated and safely transferred to the ground. When scaffolding is sheeted, the number of ties used is normally doubled. As a rule of thumb (CIRIA, 1995), the sum of B (the number of bays between each tie) × L (the number of lifts between ties) must be less than or equal to eight for unsheeted scaffolds and less than or equal to three for sheeted scaffolds. This can be expressed as:

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Head plate Reveal pin (adjustable strut – fixed horizontal of vertical) Sole plate

Transom Ledger Standards

Note: Scaffolds must not rely on revel ties for stability – a maximum of 50% reveal ties is permitted

Figure 2.53  Scaffold reveal tie.

For unsheeted scaffolds: B × L = ≤8 For sheeted scaffolds: B × L = ≤3 It is becoming common practice to construct temporary, sheeted framework over construction works that are sensitive to the weather. These temporary structures help to create a relatively stable ‘internal’ environment in which work can proceed without interruption from rain and snow. These temporary works are usually based on scaffold systems and are designed to suit specific circumstances. Independent scaffold systems Independent scaffold towers Independent scaffold towers are usually delivered to site as prefabricated units that simply clip together. Most are fabricated from aluminium, due to its light weight and easy handling properties, but steel is also used. When working above one or two lifts, outriggers are usually required to increase the stability of the tower. When using prefabricated towers, it is essential that the manufacturer’s instructions be rigorously followed. Scaffold towers have a notorious reputation for collapsing and/or falling over when overloaded or used incorrectly.

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Head plate

Tie braced to ceiling Reveal pin (adjustable steel strut – must be secure) Sole plate

Transom Ledger

Protection to cill

Transom helps improve lateral stability preventing the scaffold from moving inwards Figure 2.54  Scaffold through tie braced against floor and ceiling.

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Photograph 2.9  Through tie. The scaffold penetrates the window and is braced against the inner wall.

Birdcage scaffolding Birdcage scaffolds provide a stage with a large surface area, and is suited to high‐level work on ornate or complex ceiling structures, intricate decorative finishes to ceilings and restoration works. Birdcages stand on the floor without being tied to walls, and are therefore considered to be a type of independent scaffold system. The scaffold comprises rows of standards placed at regular intervals in a grid formation connected by ledgers. The ledgers and braces run in both directions, connecting and linking all the standards to form a cage‐like scaffold. The decking of the platform at the top of the cage is usually boarded out with two layers of scaffold planks. Each layer of planks runs at 90° to each other. The boards are laid and trapped, ensuring that there are no loose ends or gaps that would present a hazard. Polythene sheeting or dust mats are placed below the scaffold, preventing dust or small objects from falling onto those working below the cage. Birdcage scaffolds have only one working deck, which is fully boarded, and they are hence only suitable for light work. Edge protection and scaffolding for roofs Accidents occur due to people falling from the eaves of a roof, slipping down pitched roofs and over the eaves, and from people falling over the gable end of roofs. When working on

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Photograph 2.10  Proprietary system tied to building using a fixing eye.

roofs for prolonged periods of time (anything over a few hours), full edge protection should be provided. The edge protection should be designed and constructed to prevent people and materials from falling from the edges of the roof. Edge protection normally consists of guardrails and toe boards extended from an existing scaffold or installed and fixed into the perimeter walls or the edge of the roof. If scaffolding is below the eaves, additional edge boards and intermediate rails may be required to prevent people from falling over or through the scaffold. Where the roof is particularly steep, the edge protection needs to be strong and should be capable of withstanding the force of a worker and materials falling onto the scaffold. If the roof is particularly long, intermediate platforms across the slope of the roof may need to be provided. Typical methods of providing support to the edge of a roof are shown in Figures 2.55, 2.56 and 2.57.

Site Analysis, Set‐Up, Drainage and Scaffolding   83

Guard rail Steel mesh guard Intermediate rail

Scaffold board

Such arrangements are useful where space is limited, but the scaffold cannot carry load or act as a working platform Scaffolding tied and braced through the open window

Scaffold board or timber packing protects brickwork place

Figure 2.55  Scaffold: roof edge protection through open window.

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Guard rail Steel mesh guard Intermediate rail

Toe board Scaffold boards Working platform

Note: Where the projection of the roof is such that workers may fall between the scaffolding rails, two or more toe boards may be necessary

Figure 2.56  Scaffolding roofs: working platform below eaves.

Trussed‐out and suspended scaffolds It is sometimes unsafe, uneconomical or simply not practical to construct a scaffold from the ground. In such situations, trussed‐out or suspended systems are used. Trussed‐out scaffolding systems A trussed‐out scaffold is one method of scaffolding the higher levels of a building without transferring the load to the ground (Figure 2.58). Another method of high‐level scaffolding is to cantilever the loads out of the building using a secured beam (Figure 2.59). Truss and cantilever scaffolds are highly dependent on the strength of the structure. A full structural survey of the building and the designing of the scaffold must be undertaken by a competent structural engineer. With such complicated scaffolding systems, all steel tubes, fittings and

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Maximum gap between rails 470 mm

Handrail 920 – 1150 mm

Maximum gap 450 mm

Boarding to rise to line of the roof (minimum height 150 mm)

Note: Where the projection of the roof is such that workers may fall between the scaffolding rails, two or more toe boards may be necessary

600 mm Minimum width of working platform

Figure 2.57  Scaffold: dimensions for top lift of scaffold.

beams must be specially checked before and during use. All anchorage points must be securely fixed to suitable structural components of the building. Suspended scaffolds Cradles can be permanently rigged to the roof or may be temporarily installed to provide access at heights when it is not possible or simply uneconomical to erect a scaffold from the ground. Cradles and other suspended scaffold systems are becoming much more common and can be designed to suit heavy‐ and light‐duty work. The area directly below the suspended cradle should always be cordoned off, preventing people walking under the cradle from being struck by falling objects. All personnel using cradles must be trained and certified to use the equipment.

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300 mm maximum gap between building and working platform Guard rail 910–1159 mm

Head plate

Working platform

Guard rail Fibrereinforced sheeting tied to scaffold Minimum 150 toe board

Reveal pin (adjustable steel strut – must be secure) Sole plate

Transom Ledger Scaffold board sole plate

Note: Adequacy of existing structure to be checked to ensure it is able to support the loads applied by the scaffold (such scaffolding must be designed and checked by a structural engineer)

Figure 2.58  Trussed‐out scaffolding.

Ledgers Bracing

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Guard rail

Guard rail 910–1159 mm

Fibrereinforced sheeting tied to scaffold

Working platform Head plate

Minimum 150 toe board

Through tie Adjustable steel strut – must be secure

Ledgers Ledger bracing

Sole plate

Scaffolding specially designed to transfer the loads from the cantilever beam to the structure

Outer standard

Cantilevered steel beam designed to transfer loads 150 mm minimum

High-stress concentration – adequacy of structure must be checked Note: Adequacy of existing structure to be checked to ensure it is able to support the loads applied by the scaffold and cantilever beam

Figure 2.59  Cantilevered scaffolding.

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Alternative methods of access from heights Other methods of gaining access from a height include: ❏❏ ❏❏ ❏❏ ❏❏

Slung scaffolds (Figure 2.60) Bosun’s chairs Abseiling Mobile elevating work platforms (MEWPs) – for example, scissor lifts (Photograph 2.11)

Figure 2.60  Slung scaffold – suspended cradle.

Photograph 2.11  Mobile elevating work platforms (MEWP) – scissor lift.

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❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏ ❏❏

Mast climbing work platforms (MCWPs) Man‐riding skips Hoists (passenger and goods hoists) Ladders Ladder towers Stair towers (Photograph 2.12) Vehicle‐mounted platforms (cherry pickers) (Photograph 2.13)

When working at heights or from platforms, it is often necessary to have a secondary mechanism to prevent people from falling from the structure or platform. Safety harnesses and belts, clipped to sound anchorage, with personnel using shock absorbers and arrest devices, should be used. Working at heights always presents a hazard; a full risk assessment of the task should be undertaken, and all the processes and equipment used to reduce the risks must be clearly identified. In the majority of cases, personnel will need to be trained in the use of the equipment, and regular supervision is necessary to ensure that the equipment is used properly.

Photograph 2.12  Stair towers.

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Photograph 2.13  Vehicle‐mounted platforms (cherry pickers).

Ground Stability and Foundations: Chapter 3 AT A GLANCE What?  All buildings and associated structures must bear onto stable ground. The foundation of a building is that part of walls, piers and columns in direct contact with, and transmitting loads to, the ground. The foundation forms the interface between the ground and the loadbearing structure. There are four main types of foundations: strip, pad, raft and pile. Their selection is dependent on ground conditions and the design of the building. The main material used to construct foundations is reinforced concrete, which is usually cast in situ but may also be ­supplied as prefabricated units. Why?  Failure to design and construct a suitable foundation on stable ground will result in damage to the building, either through subsidence or ground heave. All new developments bear on foundations that are designed to comply with current regulations and codes. Some existing buildings have less robust foundations, and these may need to be strengthened to accommodate a change of use and the increase in loading brought about by a change of use.

When?  Investigation of the ground is necessary to establish the ground conditions and the bearing capacity of the soils and/or rock. This will inform foundation design and construction. This applies equally to new buildings and to existing buildings that are being altered or extended. Foundations are constructed after the ground has been prepared for construction. Alongside ground works and site drainage, the construction of the foundations is one of the first tasks to be completed on the construction site. How?  Each of the four main foundation types are suited to different types of building and

ground conditions. Foundations are usually constructed within excavated trenches (strip and pad foundations), on prepared ground (raft foundations) or driven into the ground (piled foundations). Ground levelling and excavation for foundation trenches is usually done by machine, or by hand in difficult‐to‐access areas and on very small developments. The foundations may be constructed onsite or delivered to site as prefabricated units to suit ground conditions and the construction schedule.

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3

Ground Stability and Foundations

The foundation of a building is that part of walls, piers and columns in direct contact with, and transmitting loads to, the ground. Early buildings were founded on rock or firm ground, and it is not unusual to find buildings without foundations when carrying out work on older properties. It was not until the beginning of the twentieth century that concrete was increasingly used as a foundation for loadbearing walls. With the introduction of local and then national building regulations, standard forms of concrete foundations have become accepted practice in the UK. This has been accompanied by more rigorous investigation of the nature and bearing capacity of soils and bedrock to inform foundation design. In this chapter, we start by looking at the nature of rocks and soils, and the stability of soils, before moving onto foundation design and a description of the four typical types of foundations: strip, pad, raft and piled. Piled foundations are usually associated with framed buildings and are described in further detail in Barry’s Advanced Construction of Buildings.

3.1  Bedrock and soil types ‘Ground’ is the term used for the Earth’s surface, which varies in composition within the following five groups: rocks, non‐cohesive soils, cohesive soils, peat and organic soils, and made‐up ground and fill. Rocks include the hard, rigid, strongly cemented geological deposits such as granite, sandstone and limestone, and soils include the comparatively soft, loose, uncemented geological deposits such as gravel, sand and clay. Soils, made‐up ground and fill are, unlike rocks, compacted under the compression of the loads of buildings on foundations. Under the imposed load of a building, rocks suffer negligible compression, and soils suffer measurable compression. The size and depth of a foundation is determined by the structure and size of the building it supports and also the nature and bearing capacity of the ground supporting it. Rocks Rocks may be classified as sedimentary, metamorphic and igneous according to their g­eological formation, as shown in Table 3.1, or by reference to their presumed bearing value (Table 3.2). Igneous rocks Igneous rocks, such as granite, dolerite and basalt, are those formed by the fusion of ­minerals under great heat and pressure. Beds of strong igneous rock occur just below or at the surface of the ground. Because of the density and strength of these rocks, it would be Barry’s Introduction to Construction of Buildings, Fourth Edition. Stephen Emmitt. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd. 93

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Table 3.1 Rocks Group

Rock type

Sedimentary Formed as particles; are laid on top of one another under pressure of the ground, air or water above

Sandstones (including conglomerates) Some hard shales Limestones Dolomite Chalk Some hard shales Slates Marble Quartzite Schists Gneisses Granite Dolerite Basalt

Metamorphic Transformation of an existing rock (metamorphism); formed owing to the high temperatures and pressures deep beneath the Earth’s surface

Igneous Formed from molten rock, magma

Table 3.2 

Bearing capacities

Group

Types of rocks and soils

Bearing capacity (kN/m2)

I Rocks

10 000

IV

1. Strong igneous and gneissic rocks in sound condition 2. Strong limestones and strong sandstones 3. Schists and slates 4. Strong shales, strong mudstones and strong siltstones 5. Clay shales 6. Dense gravel or dense sand and gravel 7. Medium‐dense gravel or medium‐ dense gravel and sand 8. Loose gravel or loose sand and gravel 9. Compact sand 10. Medium‐dense sand 11. Loose sand 12. Very stiff boulder clays and hard clays 13. Stiff clays 14. Firm clays 15. Soft clays and silts 16. Peat and organic soils

V

17. Made‐up ground or fill

II Non‐cohesive soils

III Cohesive soils

Source: Based on BS 8004:1986.

4 000 3 000 2 000 1 000 >600 >200–600 300 100–300 600 200–600 300