ROOFS and ROOFING Performance, Diagnosis, Maintenance, Repair and the Avoidance of Defects THIRD EDITION

BRE Building Elements series ROOFS AND ROOFING Performance, diagnosis, maintenance, repair and the avoidance of defects THIRD EDITION

H W Harrison, P M Trotman and G K Saunders BRE Building Elements series

ROOFS AND ROOFING Performance, diagnosis, maintenance, repair and the avoidance of defects

Third edition

H W Harrison, P M Trotman and G K Saunders CONTENTS iii

CONTENTS

Preface to the first edition v Preface to the second edition viii Preface to the third edition ix About the authors x

1 INTRODUCTION 1 1.1 Background 2 1.2 References 11

2 THE BASIC FUNCTIONS OF ALL ROOFS 13 2.1 Strength and stability 14 2.2 Dimensional stability 24 2.3 Exclusion and disposal of rain and snow 25 2.4 Energy conservation and ventilation 29 2.5 Control of solar heat and air temperature 34 2.6 Fire safety and precautions and lightning protection 42 2.7 Daylighting and control of glare 47 2.8 Sound insulation 49 2.9 Durability, ease of maintenance and whole-life costs 51 2.10 Functions particular to pitched roofs 58 2.11 Functions particular to flat roofs 62 2.12 Extensive lightweight green roofs 66 2.13 Modern methods of construction 68 2.14 Roof-mounted photovoltaic systems 70 2.15 References 73

3 SHORT-SPAN DOMESTIC PITCHED ROOFS 77 3.1 Concrete and clay tiles 78 3.2 Slate and stone tiles 108 3.3 Fully supported metal 120 3.4 Fully supported built-up bitumen felt and felt strip slates 127 3.5 Rigid sheets 132 3.6 Shingles 136 3.7 Thatch 139 3.8 Thermal insulation in lofts 147 3.9 Loft conversions 148 3.10 References 157

4 SHORT-SPAN DOMESTIC FLAT ROOFS 161 4.1 Built-up felt 163 4.2 Mastic asphalt 172 4.3 Inverted flat roofs 177 4.4 Fully supported metal roofs 180 4.5 Single-layer membranes 183 4.6 References 186 iv CONTENTS (CONT’D)

5 MEDIUM-SPAN COMMERCIAL AND PUBLIC ROOFS 189 5.1 Pitched roofs 191 5.2 Flat roofs 204 5.3 Vaults and other special shaped roofs such as glazed atria 212 5.4 Roof gardens (intensive green roofs) 219 5.5 Swimming pool roofs 221 5.6 References 223

6 MEDIUM-SPAN INDUSTRIAL ROOFS 225 6.1 Sheeted portals, north lights, monitors and saw-tooths 226 6.2 Patent glazing 237 6.3 Temporary and short-life roofs 241 6.4 References 245

7 LONG-SPAN ROOFS 247 7.1 All kinds of long-span roofs 248 7.2 Skeletal structures 254 7.3 References 258

8 INDEX 259 PREFACE TO THE THIRD EDITION ix

PREFACE TO THE THIRD EDITION

The third edition of this book is being published at a time • extensive lightweight green roofs, when the UK construction industry is facing a significant • modern methods of construction, reduction in its work load, and nearly a decade after • roof-mounted photovoltaic systems, the second edition was prepared. That decade has seen • thermal insulation in lofts, massive changes in public awareness of the need for • loft conversions, sustainability in construction, and the introduction of the • single-layer membranes. Code for Sustainable Homes in November 2006, which since May 2008 has formed a basis for assessment of the New sections have been introduced as appropriate into acceptability of the design of new housing in England and existing chapters, including: Wales. • new forms of metal roofing, But similar needs exist for the whole of the UK’s future • siphonic roof drainage, building programme, new-build hospitals, factories, • new materials technologies, educational buildings and other long-life buildings which • improved protective finishes for timber, metals and will provide challenges to designers in meeting the concrete. conditions brought about by anticipated climate changes and the need to be carbon-neutral and to conserve Where appropriate, each chapter now contains a section our dwindling natural resources. There have also been dealing with provisions that may become necessary to significant changes in British Standards which increasingly accommodate climate change (eg increased rainfall, reflect those taking place in Europe. stronger winds and higher temperatures). However, the UK cannot afford year-on-year to renew There have been considerable changes too in the more than a very small percentage of the stock of existing standards covering roof drainage which have been buildings, and the need for intelligent conservation and reflected in the revised text. upgrading of the old stock is arguably of equal if not more Approximately one-quarter of the photographs are importance. new to this edition. It is against this background that this third edition of Roofs and roofing has been prepared. In addition HWH to thorough revision of the chapters on the more PMT traditional forms of construction, such as tiling and slating, GKS completely new chapters have been prepared on: June 2009 3 SHORT-SPAN DOMESTIC PITCHED ROOFS 77

3 SHORT-SPAN DOMESTIC PITCHED ROOFS

Short-span roofs are normally • natural slate, Fibre-cement products defined as being of less than • manmade slate, 7% Slate 8–9 m span. Pitched roofs are • shingles. Clay tiles 20% conventionally defined as those 12% roofs with slopes greater than 10°, Figure 3.2 shows the current whereas roofs of slope 10° or less are market share held by the first four defined as flat. categories. Following increased For the purposes of this book, appreciation of the need to protect pitched roofs have been categorised the environment, there has been into those covered in relatively limited use of recycled materials Concrete tiles 61% small overlapping units, dealt with such as rubber. The increased in Chapters 3.1, 3.2 and 3.6, those popularity of PV systems is envisaged covered in sheet materials, dealt which will affect the type of roofing Figure 3.2: Roof tile market by value, 2006. Data from Roofing Market with in Chapters 3.3–3.5, and chosen to support them. Report[2] thatch, which forms a category of its Some general information about own, dealt with in Chapter 3.7. defects in pitched roofs in housing Small overlapping units consist of can be found in Assessing traditional the following types: housing for rehabilitation[1]. • clay tile, • concrete tile,

Figure 3.1 This steeply pitched plain tiled roof was built in 1880 but re-covered after bomb damage in the 1939–45 war PAGE3 HEADERSHORT-SPAN RIGHT DOMESTIC – Page header PITCHED subtitle ROOFS 87

Box 3.1: Calculations of rainwater run-off from short span domestic roofing BRE site inspections. Drawings have and gutter size been seen that specifically state that Using Figure 3.25, the effective catchment area that will discharge to each gutter is: the design of gutter systems should • for the slope of a pitched roof, the plan area, A (m2), plus half the elevation area, B be left to the site staff to sort out! (m2) (Figure 3.25a), The pitch of valley gutters is less than • for a pitched roof abutting a wall, the plan area, A, plus half the elevation area, B, the pitch of the roof they join, and plus half the wall area, C, above the roof slope (Figure 3.25b), valley gutters on pitches of less than • for a flat roof, the relevant plan area. 20° are particularly prone to leaking. Poor detailing was commonly found The run-off rate to each gutter is the total catchment area for the gutter divided by in the BRE quality assessments. 48. This produces the run-off in litres per second using the recommended rainfall (thunderstorm) rate of 75 mm/hour. BRE site inspections revealed a number of cases where gutters had The size of the guttering is shown in Table 3.5 using the flow capacity that will not been installed on porches and accommodate the run-off rate. As part of this process, the number of outlets should bay windows: decisions which may be considered: more outlets from a run of guttering spreads the total loading on the be marginal where the drips cause gutter, but the loadings will vary according to where the outlets are positioned (Figure 3.26). no inconvenience to the occupants, but less acceptable for doorways (Figure 3.27). (a) A room in the roof B Where a room is formed within a A pitched roof void, it is sometimes difficult to achieve adequate ventilation for the roof to the outside (Figure 3.28). BRE Defect Action Sheets 118[22] and 119[23] deal with (b) this problem, particularly where it involves the careful placing of This gutter needs to have thermal insulation to ensure an twice the flow capacity of . . . adequate ventilation gap. Thermal insulation: avoiding risks[24] is also helpful. The most important points C to watch are: • that a vapour control layer (eg of B at least 500-gauge polyethylene) A is installed in the sloping part of the roof under the insulation, • that a vapour permeable sarking is used in new construction, • that cupboards should be within the insulated envelope, ensuring continuity of the lining. . . . this gutter, and four times the Figure 3.25: Catchment areas for capacity of . . . MAIN PERFORMANCE calculating rainwater run-off REQUIREMENTS AND DEFECTS Choice of materials for Table 3.5: Flow capacities of structure standard eaves gutters (when Timber has been used as the main level) structural material in the vast majority of tiled roofs: those dating Flow capacity Size of (litres/sec) from before the early 1960s for the gutter True Nominal most part designed with strutted (mm) half round half round purlins (Figure 3.29), more recent 75 0.38 0.27 designs using trussed rafters. The 100 0.78 0.55 structure of most of these is in good 115 1.11 0.78 . . . this gutter, condition (only 1 in 8 of these 125 1.37 0.96 structures being reported as faulty[5]), 150 2.16 1.52 Figure 3.26: Spacing between outlets provided attention has been paid to reduce water load on gutters to routine maintenance of the covering.

BRE Building Elements Floors and flooring

Performance, diagnosis, maintenance, repair and the avoidance of defects

P W Pye, MRIC, CChem

H W Harrison, ISO, Dip Arch, RIBA iii Contents

Preface v Readership v Scope of the book v Some important definitions vi Acknowledgements vii Second edition vii 0 Introduction 1 Records of failures and faults in buildings 1 BRE publications on floors and flooring 5 Changes in construction practice over the years 5 1 The basic functions of all floors 11 1.1 Strength and stability 12 1.2 Dimensional stability 17 1.3 Thermal properties 20 1.4 Control of dampness and condensation, and waterproofness 25 1.5 Comfort and safety 32 1.6 Fire and resistance to high temperatures 44 1.7 Appearance and reflectivity 51 1.8 Sound insulation 53 1.9 Durability 56 1.10 Inspection and maintenance 65 2 Suspended floors and ceilings 69 2.1 Timber on timber or nailable steel joists 70 2.2 In situ suspended concrete slabs 95 2.3 Precast concrete beam and block, slab and plank floors 106 2.4 Steel sheet, and steel and cast iron beams with brick or concrete infill 116 2.5 Masonry vaults 124 2.6 Platform and other access floors 128 3 Solid floors 133 3.1 Concrete groundbearing floors: insulated above the structure or uninsulated 134 3.2 Concrete groundbearing floors: insulated below or at the edge of the structure 151 3.3 Rafts 154 iv Contents

4 Screeds, underlays and underlayments 157 4.1 Dense sand and cement screeds: bonded and unbonded 158 4.2 Floating screeds: sand and cement 166 4.3 Levelling and smoothing underlayments 170 4.4 Lightweight screeds 172 4.5 Screeds based on calcium sulfate binders 174 4.6 Matwells, duct covers and structural movement joints 177 5 Jointless floor finishes 181 5.1 Concrete wearing surfaces 182 5.2 Polymer modified cementitious screeds 186 5.3 Granolithic and cementitious wearing screeds 188 5.4 In situ terrazzo 191 5.5 Synthetic resins 194 5.6 Paints and seals 199 5.7 Mastic asphalt and pitchmastic 202 5.8 Magnesium oxychloride (magnesite) 206 6 Jointed resilient finishes 211 6.1 Textile 212 6.2 Linoleum 215 6.3 Cork 218 6.4 PVC flexible 220 6.5 PVC semi-flexible or vinyl (asbestos) 226 6.6 Rubber 229 6.7 Thermoplastic 232 7 Jointed hard finishes 235 7.1 Ceramic tiles and brick paviors 236 7.2 Concrete flags 245 7.3 Natural stone 247 7.4 Terrazzo tiles 252 7.5 Composition block 256 7.6 Metal 260 8 Timber and timber products 263 8.1 General 264 8.2 Board and strip 268 8.3 Block 272 8.4 Parquet and mosaic 275 8.5 Panel products 277 Appendix A How to identify less recognisable floorings and their substrates 283 Appendix B How to choose a flooring 284 References and further or general reading 285 Index 295 v Preface

First edition of the underlying structure to enable procedures – or until they make the an understanding of the behaviour of mistakes, or overlook precautions, as It has been said that most problems the whole floor without going very previous generations have done. with floors occur because people far into engineering design The criteria presented in Chapter 1 insist on walking on them, pushing principles. It does not purport, are then related to the different trolleys over them, placing large though, to be a book of construction types of floors and their finishes objects on them and dropping things practice; nor does it provide the (Chapters 2–8). on them – if only they were ceilings reader with the information The text concentrates on those they would never wear out! A small necessary to design a floor, but, aspects of construction which, in the witticism that reflects the way some mainly through lists and experience of BRE, lead to the people, including professionals in comprehensive illustration, shows greatest number of problems or the construction industry, see floors. him or her what to look for as good greatest potential expense if carried Or, rather, don’t see them! After all, and bad features of floors and out unsatisfactorily. It follows that what is there to a floor: floorboards flooring. It also offers sources of these problems will be picked up nailed to joists. What can go wrong further information and advice. most frequently by maintenance with that? And if it happens to form surveyors and others carrying out a ceiling, even better. But the facts Readership remedial work on floors. Although belie this perception. Floors and flooring is addressed most of the information relates to BRE’s figures on faults in primarily to building surveyors and older buildings, surveyors may be buildings of all types (given in other professionals performing called upon to inspect buildings built greater detail in the introductory similar functions, such as architects in relatively recent years. It is chapter which follows) show that a and builders, who maintain, repair, therefore appropriate also to include substantial number concern floors. extend and renew the national much material concerning Despite the advice that has been building stock. Lecturers and other observations by BRE of new available to the industry from the educators in the building field will buildings under construction in the 1920s, faults in flooring, such as also find it to be a useful adjunct to period 1985–95. cracking, detachment and entrapped their course material. Many of the difficulties which are water, recur frequently. If some of referred to BRE for advice stem the errors appear elementary, this Scope of the book from too hasty assumptions about only reflects what happens in the Although books on flooring are few, the causes of particular defects. Very design office and on site. All that we there is no shortage of industry often the symptoms are treated, not can do is show to those who work in guidance on floors and flooring. The the causes, and the defects recur. It is the flooring industry what is being problem is that people do not use the to be hoped that this book will done incorrectly and how to take guidance that exists. encourage a systematic approach to corrective action – preferably before To try to remedy that situation, the diagnosis of floor and flooring faults or defects lead to costly the contents of this book are defects. damage. configured so that the principles, The case studies provided in some This book describes the materials features and functions of floors and of the chapters are selected from the and products, methods and criteria flooring are described first files of BRE Advisory Service and which are used in the construction of (Chapter 1). There needs to be the former Housing Defects floors and flooring. It draws the sufficient discussion of principles to Prevention Unit, and represent the reader’s attention to those elements impart understanding of the reason most frequent kinds of problems on and practices which ensure good for certain practices; without that which BRE is consulted. They are performance or lead to faults and understanding, practitioners will not meant to be comprehensive in failure. There is sufficient discussion have difficulty following correct scope since the factors affecting vi Preface individual sites are many and varied. Ramps, landings and stair treads We have deliberately not provided As has already been said, this are included as elements of floors, more than an outline of the major book is not a textbook on building but not staircase enclosures. There is points which specifiers will need to construction. Hence, the drawings an argument for dealing with take into account in the cleaning and are not working drawings but merely staircases in conjunction with walls maintenance of floorings since this is show either those aspects to which since, in most cases, it is necessary to not a topic which has been studied in the particular attention of readers consider the enclosures for stairs in depth by BRE or its predecessor, the needs to be drawn or simply provide conjunction with stair flights; Building Research Station; in any typical details to support text. enclosures for staircases, and such case there is suitable literature Other more specific aspects of the matters as protected shafts, are available from industry sources and subject not deemed to be relevant to therefore considered as elements of other publishers. this book are mentioned briefly in walls. appropriate chapters – usually in the Much that is relevant to ordinary Some important definitions introductory paragraphs. floor finishes applies also to stair Some of the more general terms Passive fire protection measures tread finishes. used in floors and ceilings will be are those features of the fabric, such The weatherproofing aspects of found in Section 1.3, Subsection 1.3.3 as structural frames, walls and floors, balconies, insofar as they are similar of BS 6100-1 (Glossary of building that are incorporated into building to those of roofs, are dealt with in the and civil engineering terms: General design to ensure an acceptable level book on roofs. Thresholds are and miscellaneous). of safety. These measures, so far as handled as parts of external walls. Since the book is mainly about the they affect floors, are dealt with in In many places through the book problems that can arise in floors, two outline in this book. Measures which we have quoted British Standards words, ‘fault’ and ‘defect’, need are brought into action on the and codes of practice which have precise definition. Fault describes a occurrence of a fire, such as fire been withdrawn; however they departure from good practice in detectors, sprinklers and smoke would have been current at the time design or execution of design; it is exhaust systems are referred to as a particular floor or flooring was laid. used for any departure from active fire protection, and are not We have done this deliberately since requirements specified in building dealt with in this book. they often gave better specifications regulations, British Standards and The standard headings within the than those now current. Indeed, in codes of practice, and the published chapters are repeated only where some cases, standards and codes recommendations of authoritative there is a need to refer the reader have been withdrawn and not organisations. A defect – a shortfall back to earlier statements or where replaced. Copies of old standards in performance – is the product of a there is something relevant to add to and codes are often retained by BRE fault, but while such a consequence what has gone before. We have for use in disputes; they can also be cannot always be predicted with assumed that readers will know seen in the British Library. certainty, all faults should be seen as many of the more common In the United Kingdom, there are having the potential for leading to abbreviations used in the industry – three different sets of building defects. The word ‘failure’ has DPC, PVC etc – and we have regulations: the Building Regulations occasionally been used to signify the declined to spell them out. 1991 which apply to England and more serious defects. This book deals with all kinds of Wales; the Building Standards By ‘floor’ we mean the whole of floorings (ie floor coverings), (Scotland) Regulations 1990; and the the horizontal elements of a building including both in situ and Building Regulations (Northern (excluding roofs but including manufactured products, and these Ireland) 1994. There are many ceilings); ‘flooring’ refers simply to are covered in detail in Chapters 5–8. common provisions between the the finish of the upper surface of the A classification of floorings for use three sets, but there are also major floor. internationally has been published differences. Although the book has Where the term ‘investigator’ has by the European Union of been written against the background been used, it covers a variety of roles Agrément, and this is examined in of the building regulations for including a member of BRE’s more detail later in the book. England and Wales, this is simply Advisory Service, a BRE researcher Ceilings, whether suspended or because it is in England and Wales or a consultant working under applied directly to soffits, are treated that most BRE site inspections have contract to BRE. as integral parts of the element of been carried out. The fact that the floors since many aspects of majority of references to building performance, such as fire and sound, regulations are to those for England affect all parts of both floors and and Wales should not make the book ceilings. Ceilings are mainly dealt inapplicable to Scotland and with in Chapter 2. Northern Ireland. Preface vii

‘Topping’ has been used to Acknowledgements Second edition describe an in situ material laid to Photographs which do not bear an provide good abrasion resistance attribution have been provided from This revised edition of Floors and and to provide the wearing surface. our own collections or from the BRE flooring embodies a considerable It has also been used to refer to a Photographic Archive, a unique number of changes from the first cementitious mix used to lock collection dating from the early edition, particularly with respect to together components of a structural 1920s. changes to standards and codes, and concrete floor, such as hollow pots, To the following colleagues – to building regulations. where it is called a structural many from the BRE Scottish Major changes will be found to topping. Laboratory and the Fire Research the section concerned with revised ‘Underlay’ is a layer used between Station – and former colleagues who guidance for identifying radon the structural deck or slab and the have suggested material for this affected areas (Chapter 1.5); to the flooring, either prefabricated (eg book or commented on drafts or section on tests for sound insulation plywood or hardboard) or a thick in both, we offer our thanks: which has been amended by the situ layer (eg mastic asphalt or D R Addison, Dr B R Anderson, introduction of pre-completion aggregate filled latex cement). R W Berry, Dr A B Birtles, testing (PCT) by Approved ‘Underlayment’ is in situ material Dr P Bonfield, P J Buller, Document E (2003) of the Building used to smooth or level the base Dr R N Butlin, A H Cockram, Regulations (Chapter 1.8); and to prior to laying the flooring. (The Dr J P Cornish, S A Covington, the chapter on panel products term underlay seems to have R N Cox, Dr R C deVekey, (Chapter 8.5) following the become restricted to preformed Diane M Currie, R J Currie, preparation of performance substrates and the term Maggie Davidson, specifications and confirmation of underlayment to those formed in Dr J M W Dinwoodie, former draft International Standards. situ, and we have adopted this Dr B R Ellis, Dr V Enjily, The opportunity has also been distinction. However, in other Dr L C Fothergill, E Grant, taken to update references to the industry publications and documents G J Griffin, C J Grimwood, J H Hunt, hundred or so British Standards the former term will be found to Dr P J Littlefair, T I Longworth, mentioned in the first edition. apply to both applications.) K W Maun, N O Milbank, ‘Wear’ is the progressive loss from Dr D B Moore, W A Morris, PWP the surface of a material or Dr R M Moss, F Nowak, HWH component brought about by E F O’Sullivan, R E H Read, J F Reid, July 2003 mechanical action. M R Richardson, J Seller, A J Stevens, P M Trotman, C H C Turner and Dr T J S Yates, all of BRE. We have also drawn upon some notes prepared by the late Dr Frank Harper and the late Wilfred Warlow. In addition, we acknowledge the contributions of the original, though anonymous, authors of Principles of modern building, Volume 2, from which several passages have been adapted and updated.

PWP HWH August 1997 56 1 The basic functions of all floors Chapter 1.9 Durability

This is a general chapter which includes information relevant to all kinds of flooring – information relevant to a particular kind of flooring, such as typical wear rates on a particular surface, will be given in the appropriate later chapter. Floor finishes may be considered to provide for the following main functions: G protection of the structural floor G better appearance G increased comfort and safety

The relative importance of these functions varies according to circumstances and budgets. Figure 1.61 However, one of the most important This industrial floor has suffered very heavy attributes is the maintenance of the wear in spite of the robust finish. It has functions over time; in other words, been subjected to piecemeal replacement. the finishes must be durable. Because The wheel tracks of mechanical handling of its importance, durability has equipment can be seen often been regarded as a basic property of a floor finish, but it represents only the length of time The European Union of that the chosen properties persist Agrément (UEAtc) have given and depends as much on the priority, in their Method of conditions of use as on the Assessment and Test covering properties of the finish(98). innovative floorings, to assessing the Many factors influence the life of conditions of service for floorings a floor finish: using what has been called the G wear UPEC system. UPEC is the French G water and other liquids acronym for wear (usure) index 1–4, G indenting loads and impacts indentation (poinçonnement) index (Figure 1.61) 1–3, water (eau) index 0–3, and G sunlight chemicals (chimiques) index 0–3 G insects (UEAtc Method of Assessment and G moulds and fungi Te st No 2 (25)). Given the existence of G high temperature an Agrément certificate for a particular product, therefore, a as well as the fundamental properties surveyor should be able to make a Figure 1.60 of the materials and adhesives used, judgement on its performance. The durability of any flooring is governed and the compatibility of these with UEAtc and the British Board of ultimately by the kind of use it gets, other parts of the structure and its Agrément (BBA) have also issued particularly by heavy wheeled vehicles behaviour in use. further guidance on the assessment 1.9 Durability 57

selected flooring, taking all involved, the assessment becomes circumstances into account. What more and more subjective. that minimum might be is a matter Wear and damage can be for debate, but UEAtc have decided considered to arise from a number of on 10 years, and BRE would not causes: dispute that figure(25). G mechanical action (leading to Durability is affected by the care progressive loss of substance) and skill with which the floor is laid, G abrasion caused by fine solid and the behaviour of the subfloor, as particles well as by the choice of material G cutting by the action of vehicles itself. Failure to provide adequate (eg trolleys) and furniture dampproofing and ventilation, and a G corrosion from spillages Figure 1.62 sound screed, can lead to serious G degradation from soluble salts This paint finish is breaking up. There is deterioration in finish; for example rising from the subsoil or little substance to resist further wear as buckling of wood block floors or entrapped moisture in concrete loss of adhesion in tiled or painted G fatigue in the surface material finishes (Figure 1.62). G movement or rocking from of plastics floorings (UEAtc uneven or friable bedding causing Methods of Assessment and Test Resistance to wear chipping of arrises of slabs or tiles No 23(99) and No 36(100), and BBA All floor surfaces wear to some Information Sheet No 2(101)). These degree when subjected to foot or There has been considerable are referred to in greater detail in the wheeled traffic. There may also be concern since the 1960s with the appropriate later chapters. other factors including the degree of wear of floors in heritage Experience has shown that there is a movement of furniture, which may buildings. This is dealt with in detail relationship between wear and scrape or cut the surface, and the in Chapters 5.2 and 5.5. In some indentation of PVC floorings; these movement of heavy loads such as in cases, depending of course on the floorings, invariably, have a C index warehouses. However, using the material involved, it is evident that of 2. For PVC floorings, it has definition of wear as the progressive wear of around one millimetre in ten therefore been found possible to loss from the surface of a body years is occurring(103). omit the C rating, and to combine brought about by mechanical action, the U and P ratings into a single G it is not just the quantitative loss of classification (1–5). material which is important but also Of all the performance factors the qualitative assessment of the described above, wear is perhaps the condition of the worn surface. most influential because: Where changes in appearance are G it is unavoidable in normal use G it applies to all kinds of flooring G in many cases, it can be very obvious to users when it occurs

Expected life of floorings There is a British Standard on durability, BS 7543(102), which applies to floors and flooring. It gives general guidance on required and predicted service life, and how to present these requirements when preparing a design brief. The service life of a floor covering depends as much on the conditions in the building and the degree of use as on the inherent properties of the material and the techniques adopted in laying it. However, even bearing in mind the comparative ease of replacement of many thin floorings, building users should have a Figure 1.63 reasonable expectation of a Measuring the forces applied by foot traffic to flooring. Although these tests were minimum service life for a properly conducted in the late 1950s, the results still apply

BRE Building Elements Walls, windows and doors

Performance, diagnosis, maintenance, repair and the avoidance of defects

H W Harrison, ISO, Dip Arch, RIBA

R C de Vekey, PhD, MRIC, CChem, DIC

BRE Garston Watford

WD2 7JR iii Contents

Preface v Readership v Scope of the book v Some important definitions vi Acknowledgements vi 0 Introduction 1 Records of failures and faults in buildings 1 BRE Defects Database records 3 BRE publications on walls, windows and doors 9 Changes in construction practice over the years 9 1 The basic functions of the vertical elements 15 1.1 Strength and stability 16 1.2 Dimensional stability 24 1.3 Exclusion and disposal of rain and snow 28 1.4 Thermal properties and condensation 38 1.5 Ventilation and air leakage 44 1.6 Daylighting, reflectivity and glare 46 1.7 Solar heat, control of sunlight and frost 49 1.8 Fire 54 1.9 Noise and sound insulation 58 1.10 Safety and security 61 1.11 Durability and maintenance 65 1.12 Anthropometrics and dynamics 74 2 Loadbearing external walls and units 77 2.1 Brick, solid 78 2.2 Brick and block, cavity 90 2.3 Stone rubble and ashlar 103 2.4 Precast concrete 108 2.5 In situ concrete 116 2.6 Earth, clay and chalk 120 iv Contents

3 External cladding on frames 125 3.1 Masonry on steel or concrete frame 126 3.2 Precast concrete on steel or concrete frame 132 3.3 Timber frame 137 3.4 Sheet cladding over frames 148 3.5 Glass fibre reinforced polyester and glass fibre reinforced cement 163 4 Glazing and curtain walling 167 4.1 Domestic windows 168 4.2 Non-domestic windows 183 4.3 Curtain walling and glass blocks 187 5 External doors, thresholds and shutters 193 5.1 Hinged, pivoting and sliding pedestrian doors 194 5.2 Thresholds 199 5.3 Garage doors, shutters and gates 203 6 Separating and compartment walls 207 6.1 Brick and block, precast and in situ concrete 208 6.2 Framed 215 6.3 Stairway enclosures and protected shafts 218 7 Partitions 221 7.1 Masonry partitions 222 7.2 Framed, movable and relocatable partitions 227 8 Internal doors 233 8.1 Doors for normal traffic 234 8.2 Fire doors 239 9 Applied external finishes 243 9.1 Tiling 244 9.2 Rendering 248 9.3 Timber and plastics cladding 259 9.4 Paints and other liquid or plastic finishes 262 10 Applied internal finishes 267 10.1 Tiling 268 10.2 Plastering and rendering 271 10.3 Sheet and board finishes 275 10.4 Paints and other liquid or plastic finishes 279 References and further or general reading 281 Index 295 v Preface

This book is about all the main cases an underlying cause is lack of walls, windows and doors and the vertical elements of buildings, both knowledge, in others a lack of care. joints between them are described, external, including walls, windows and sources of further information and and doors, and internal, including Readership advice are offered. The drawings are separating walls, partitions and Walls, windows and doors is not working drawings but merely internal doors. It deals in outline with addressed primarily to building show either those aspects to which the the achieved performances and surveyors and other professionals particular attention of readers needs to deficiencies of the fabric over the performing similar functions – such as be drawn or simply provide typical whole age range of the national architects and builders – who details to support text. building stock. Of course, many maintain, repair, extend and renew the Excluded from the scope of this performance requirements are national building stock. It will also book is consideration of foundations common to buildings of whatever age, find application in the education field. for walls, or basements, which will be the main difference being that In spite of the current explosion dealt with in another publication. occupants tend to make allowances of information, or perhaps because of Wall-to-roof junctions at eaves and for deficiencies when the building it, people do not use the guidance that verges, and fabric or flexible plastics is old. exists. In order to try to remedy that sheathings to buildings were dealt The construction of a wall and its situation, the advice given in Chapters with in the companion book, Roofs constituent materials must have 2 to 10 of this book concentrates on and roofing. adequate strength, be fire resistant, practical details. However, there also As with the other books in this offer the necessary acoustic and needs to be sufficient discussion of series, the text concentrates on those thermal properties, and resist erosion principles to impart understanding of aspects of construction which, in the and corrosion for the life of the the reason for certain practices, and experience of BRE, lead to the building, so that the occupants can use much of this information is given in greatest number of problems or the building safely and conveniently. Chapter 1. greatest potential expense, if carried In addition, the external envelope out unsatisfactorily. It follows that should have adequate resistance to the Scope of the book these problems will be picked up most elements, and must allow the All kinds of external walls, frequently by maintenance surveyors maintenance of a suitable indoor encompassing loadbearing and non- and others carrying out remedial work environment. loadbearing, curtain walls, and on walls, windows and doors. Information on faults in buildings overcladding are dealt with first; then Occasionally there is information of all types show that nearly half windows and external doors, relating to a fault which is concern walls, windows and doors. including thresholds. Later chapters infrequently encountered, and about Despite the advice that has been include separating walls, partitions, which it may in consequence be available to the industry from the and internal doors and stair enclosures difficult to locate information. 1920s, faults which formerly occurred including protected shafts. In Although most of the information on a substantial scale, such as rain principle, all types of buildings are relates to older buildings, much penetration through included, though obvious practical material concerning observations by windows and doors, still recur considerations of space decree that BRE of new buildings under frequently. Some of these faults may information on heritage buildings is construction in the period from 1985 appear to be elementary in character, limited in scope. to 1995 is also included. but this only reflects The book is not a manual of Many of the difficulties which are what happens in practice. Recognition construction practice, nor does it referred to BRE for advice stem from of faults before they occur on site is provide the reader with the too hasty an assumption about the obviously much more preferable to information necessary to design a causes of a particular defect. Very correction after the event. In some wall. Both good and bad features of often the symptom is treated, not the vi Preface cause, and the defect recurs. It is to be that the majority of references to still in current use, we prefer to use it hoped that this book will encourage a building regulations are to those for in this book as a generic term despite systematic approach to the diagnosis England and Wales, should not make the comparable term ‘compartment of walls and walling defects. the book inapplicable to Scotland and wall’ which is found in the national The case studies provided in some Northern Ireland. building regulations. of the chapters are selected from the There is insufficient space in this files of the BRE Advisory Service and book to deal with the highly Acknowledgements the former Housing Defects sophisticated new forms of external Photographs which do not bear an Prevention Unit, and represent the walls, such as the so-called ‘smart’ or attribution have been provided from most frequent kinds of problems on intelligent skins, employing variable our own collections or from the which BRE has been consulted. external fabric, to improve solar BRE Photographic Archive, a unique The standard headings within the control and daylight utilisation. It is collection dating from the early chapters are repeated only where there intended that these form part of a 1920s. is a need to refer the reader to earlier further book in this series. To the following colleagues, and statements or where there is Information relating to these former colleagues, who have something relevant to add to what has techniques may be sought from BRE. suggested material for this book or gone before. commented on drafts, or both, we Since it is necessary to consider the Some important definitions offer our thanks: enclosures for stairways in Since the book is mainly about the M J Atkins, P Bonfield, R Cox, conjunction with stair flights, problems that can arise in walls, E J Daniels, Maggie Davidson, enclosures for stairways (including windows and doors, two words, ‘fault’ C Grimwood, W H (Bill) Harrison, C such items as protected shafts) are and ‘defect’, need precise definition. Holland, M Howarth, therefore considered as elements of Fault describes a departure from good Dr P Littlefair, Penny Morgan, walls and are dealt with in this book in practice in design or execution of F Nowak, Dr R Orsler, M Pound, Chapter 6.3. design: it is used for any departure P W Pye, R E H Read, J Reid, In the United Kingdom, there are from requirements specified in Justine Redshaw, B Reeves, J Seller, three different sets of building building regulations, British A J Stevens, C M Stirling, regulations: The Building Regulations Standards and Codes of practice, and N Tinsdeall, P M Trotman, P Walton, 1991 which apply to England and the published recommendations of and Dr T Yates, all of the BRE. Wales; The Building Standards authoritative organisations. A defect – We wish to acknowledge a special (Scotland) Regulations 1990; and The a shortfall in performance – is the debt to P M Trotman for providing the Building Regulations (Northern product of a fault, but while such a majority of the information in Chapter Ireland) 1994. There are many consequence cannot always be 2.6. common provisions between the three predicted with certainty, all faults In addition, acknowledgement is sets, but there are also major have the potential for leading to given to the original though differences. This book has been defects. The word failure has anonymous authors of Principles of written against the background of the occasionally been used to signify the modern building, Volume 1, from building regulations for England and more serious defects (and which several passages have been Wales since, although there has been catastrophes!). adapted and updated. an active Advisory Service for Where the term 'investigator' has Scotland and Northern Ireland, the been used, it covers a variety of roles H W H highest proportion of site inspections including a member of BRE's R C de V has been carried out in England and Advisory Service, a BRE researcher July 1998 Wales. In addition, the technical or a consultant working under contract aspects of the book are affected more to BRE. by exposure due to location and height Because the term ‘separating wall’ above sea level than by national or has been used in the construction administrative boundaries. The fact industry from the earliest days, and is 15 Chapter 1 The basic functions of the vertical elements

Figure 1.1 Tay House, Glasgow (Photograph by permission of Stoakes Systems Ltd)

This first chapter deals in turn with the basic functions which affect all of the vertical external envelope of a building, whether large (Figure 1.1) or small, and all of its vertical internal subdivisions. In later chapters each of these functions is considered in greater detail where relevant to a particular component. The chapter takes its cue from a passage in Principles of modern building: ‘It will be convenient to consider the whole range of wall functions together, even though any given wall, external or internal, loadbearing or non-loadbearing, may not have to perform all of them’. 16 1 The basic functions of the vertical elements Chapter 1.1 Strength and stability

The predominating factor in the building, or such movement of the design of a wall is whether it has to ground, as will impair the stability of carry an imposed load, for example any part of another building from floors and roofs. Ever since (2) In assessing whether a building Roman times the loading on a non- complies with sub paragraph (1) framed wall has largely governed its regard shall be had to the imposed and thickness, and over the years wind loads to which it is likely to be conventions became established for subjected in the ordinary course of its their construction. use for the purpose for which it is However, it is only comparatively intended.’ rarely that the wall can stand by itself Structural design of walls for without receiving support or restraint buildings is covered by the main from the remainder of the building. British Standard Codes of practice for Even the smaller domestic scale the various materials: building of loadbearing brick often ● steel to BS 5950-1 to 9(16) relies on the floor to provide lateral ● concrete to BS 8110-1 to 3(17) restraint to the external wall. All that ● timber to BS 5268(18) this chapter can do is to draw attention ● masonry to BS 5628(19), Approved to some of the more important Document 1/2(20) or BS 8103(21) considerations in relation to the contribution which walls make to the Loads structure as a whole, but not to provide There is a wide range of structural sufficient information to allow the considerations that may be structural design of walls to be carried required of a walling system, ranging out. from purely non-loadbearing cladding All walls need to be sufficiently to the cellular masonry or concrete strong to carry the self weight of the walling system which ultimately structure, together with imposed carries all the actions on a structure. loads; for example those due to The forces are illustrated by Figure furniture, equipment or the occupants 1.2.

Shear (in plane) of the building. Current requirements as far as the Dead loads Compressive structure of walls is concerned are The dead weight of any floors,

Shear embodied in the various national partitions, ceilings, roofs and (in plane) building regulations. Taking the claddings must be carried to the England and Wales Regulations(15) as ground (foundations) via a structural an example: frame or a loadbearing wall. The ‘(1) The building shall be design dead load at any point is the constructed so that the combined sum of all the individual dead loads Lateral (flexural) dead, imposed and wind loads are acting at that point from above sustained and transmitted by it to the factored up to allow for the variability Shear ground of materials. The partial factor of (normal) (a) safely; and safety is normally around 1.2–1.4 for Figure 1.2 (b) without causing such deflection unfavourable loads and 0.9 for Different loadings on a wall or deformation of any part of the favourable loads. Eccentric loads

BRE Building Elements Foundations, basements and external works

Performance, diagnosis, maintenance, repair and the avoidance of defects

H W Harrison, ISO, Dip Arch, RIBA

P M Trotman

BRE Garston Watford

WD25 9XX iii Contents

Preface v Readership v Scope of the book v Design criteria vi Some important definitions vi Acknowledgements vii 0 Introduction 1 Records of failures and faults in buildings 2 BRE Defects Database records 2 BRE publications on foundations, basements and external works 4 Changes in construction practice over the years – a historical note 6 Summary of main changes in common practice since the 1950s 11 Building user requirements in the third millenium 14 1 The basic features of sites 15 1.1 Geology and topography 17 1.2 Fill, contaminated land, methane and radon 43 1.3 Surface water drainage requirements, water tables and groundwater 57 1.4 Site microclimates; windbreaks etc 62 1.5 The effects of vegetation on the ground 70 2 Foundations 77 2.1 General points on foundations 79 2.2 Old brick and stone footings 109 2.3 Concrete strips, pads etc 112 2.4 Piles 121 3 Basements, cellars and underground buildings 129 3.1 Structure 132 3.2 Waterproofing 138 3.3 Other aspects of performance 150 iv Contents

4 Public and other utilities 157 4.1 Water supply 158 4.2 Wastewater drainage 162 4.3 Surface water drainage, soakaways and flood storage 185 4.4 Other utilities 193 5 Walls, fencing and security devices 195 5.1 Embankments and retaining walls 196 5.2 Freestanding walls 206 5.3 Fencing 212 5.4 Exterior lighting and security devices 220 6 Hard and soft landscaping 225 6.1 Pavings 227 6.2 Trees, plants and grass 233 References and further reading 239 Index 249 v Preface

This book is the fifth of the BRE experience of individual surveyors. Large civil engineering Building Elements books and Clients need to be advised on when to structures such as port installations, completes the planned series which call in other consultants to rectify bridges and tunnels, underground car was begun in 1996. The first four existing problems. The book is parks and very large non-building books are Roofs and roofing (first certainly not addressed to the structures such as storage tanks are published in 1996), Floors and geotechnical engineer or the excluded from the scope of this book. flooring (1997), Walls, windows and landscape architect, though it will in Included in external works are all doors (1998) and Building services all probability find application in the items outside the building footprint (2000). education field. but inside the site boundary, encompassing wastewater and surface Readership Scope of the book water drains, supply of utilities (eg As with the other books, Foundations, The descriptions and advice given in gas, electricity and cabled services), basements and external works is this book concentrate on practical footpaths, and access for vehicles addressed primarily to building details. But there also needs to be including car parks and hard standings surveyors and other professionals sufficient discussion of principles to to be found in the vicinity of performing similar functions; for impart understanding of the reason for buildings. Perimeter and freestanding example, architects and builders who certain practices. In previous books in boundary walls are also dealt with, as maintain, repair, extend and renew the this series, some of the information is security fencing and, in outline national building stock. Surveyors and which applied generally to the subject only, lighting; CCTV surveillance architects undertaking routine surveys matter of the book was given in systems, though, are normally left in of existing buildings may identify site Chapter 1, but here the topics, though the hands of specialist consultants and problems or issues – in particular all closely related to the site, are rather contractors, and are therefore not concerning the behaviour of more disparate, and the principles covered in detail. foundations – which need to be which govern practice will in With such a broad scope, it will be referred to specialists for advice. consequence be found dispersed in apparent that only brief reference can The larger non-domestic buildings individual chapters. be made to most topics, and the text built in the second half of the Included in foundations and therefore concentrates on those twentieth century, and perhaps even basements is all work below DPC aspects with which BRE has been some in the first half of the century – level, including strip foundations, most heavily involved, whether in the standard textbooks of the time piles, retaining walls to basements; laboratory research, site investigation were quite explicit – will most likely but not including ground floor slabs or or development of legislation. have had the benefit of adequately rafts, which were included in Floors In principle, all types of buildings designed foundations. In the case, and flooring, and building services are included. However, it is inevitable though, of relatively small buildings within the footprint of the building, that the nature of foundations such as houses, many decisions which were included in Building becomes very sophisticated in some concerning ground and foundations services. building types such as those which are will have been made by building Many points relating to the use of very tall, and these installations rarely professionals who had little or no particular materials in close proximity lend themselves to simple guidance training in geotechnical engineering. to the ground, such as the durability of for use by non-specialists. Indeed, Some topics, such as deterioration brick, block and concrete have been there may well be no professional role in drainage installations, may often be dealt with in Walls, windows and whatsoever for them in this respect. amenable to straightforward doors to which reference can be made. However, even the relatively simple rectification, but other aspects, such systems used in the majority of as the installation of dampproofing in domestic construction provide basements, may be outside the adequate potential for improvement. vi Preface

Foundations, basements and material to be described requires a Design criteria external works is not a manual of further breakdown into diagnosis, While this book is mainly about construction practice, nor does it monitoring and remedial work. existing buildings and not specifically provide the reader with the Chapter 3 also does not follow the about the design of new buildings, it information necessary to design standard headings; it was found to be has been necessary in several foundations, basements or external more appropriate to deal separately circumstances to give some design works. Both good and bad features of with structure and waterproofing of criteria so that subsequent these elements are described, and basements which is reflected in the performance of the completed sources of further information and sub-chapter headings. building may be assessed against what advice are offered. The drawings are In the United Kingdom, there are was required or intended. not working drawings but merely three different sets of building show either those aspects to which the regulations: The Building Regulations Some important definitions particular attention of readers needs to 1991 which apply to England and The term ‘footprint’ has been used to be drawn, or simply provide typical Wales; The Building Standards describe the area actually covered by details to support text. The discussion, (Scotland) Regulations 1990; and The the building fabric. Note that this term for the most part, is deliberately Building Regulations (Northern is not synonymous with the term neutral on matters of style and Ireland) 1994. There are many curtilage, as used in legislation, which aesthetics and is wary of suggesting common provisions between the three in its normally accepted meaning that there is ever a unique optimum sets, but there are also major includes any ground forming a part of solution. differences. The book has been the enclosure within which the In a similar fashion to the other written against the background of the building stands. books in this series which deal with building regulations for England and The term ‘surcharge’ as used in this other building elements, the present Wales, since, although there has been book has two distinct meanings: a text concentrates on those aspects an active Advisory Service for preloading of the ground (eg to induce relating to the subject matter of the Scotland and Northern Ireland, the consolidation), and a condition in book, in this case the site, and which, highest proportion of site inspections which water is held under pressure in the experience of BRE, lead to the has been carried out in England and within a gravity drain, but which does greatest number of problems or Wales. The fact that the majority of not escape to cause flooding. greatest potential expense if carried references to building regulations are So far as water terms are concerned, out unsatisfactorily. It follows that to those for England and Wales should there has been a significant change in these problems will be picked up most not make the book inapplicable to usage since the 1980s. The term frequently by maintenance surveyors Scotland and Northern Ireland. ‘potable water’ to describe water of a and others specifying and carrying out Although practically all topics quality suitable for drinking is now no remedial work. Occasionally there is relating to the construction of longer popular though it is still information relating to an item, buildings are encompassed in the contained in current Standards, and perhaps a fault, which is infrequently Construction (Design and the words ‘drinking’ and ‘wholesome’ encountered, and about which it may Management) Regulations 1994, the to describe water are preferred. be difficult to locate information. ramifications for each of the topics The use of the term ‘foul water’ in Although most of the information covered in this book are quite relation to sewage has fallen out of relates to older buildings, much different. It is therefore not practical official use, being superseded by the material concerning observations by to spell them out, beyond noting that term ‘wastewater’ which is often more BRE investigators of new buildings there must be a Health and Safety Plan closely defined as ‘greywater’ or under construction in the period from and File for all construction work ‘blackwater’; ‘greywater’ is 1985 to 1995 is also included. which should include information on wastewater not containing faecal The case studies provided in some how to manage health and safety matter or urine, ‘blackwater’ is of the chapters are selected from the issues after the installation is wastewater that contains faecal matter files of the BRE Advisory Service, completed and throughout its life until or urine. However, for the purposes of and the former Housing Defects demolition(1). this book, we tend to retain the term Prevention Unit, and represent the foul water when referring to most frequent kinds of problems on greywater and blackwater; which BRE has been consulted. wastewater, though, can include The standard headings within the surface water (eg run-off from car chapters are repeated only where there parks). is a need to refer the reader to earlier The term ‘aerobic’ indicates statements or where there is conditions in which free oxygen is something relevant to add to what has present, and ‘anaerobic’ in which it is gone before. An exception to the not present. sequence of standard headings occurs in Chapter 2.1 where the amount of Preface vii

Since the book is to a considerable Acknowledgements extent about the problems that can Photographs which do not bear an occur in the below-ground fabric of attribution have been provided from buildings, two words, ‘fault’ and our own collections or from the ‘defect’, need precise definition. Fault BRE Photographic Archive, a describes a departure from good unique collection dating from the early practice in design or execution of 1920s. design; it is used for any departure To the following colleagues, and from requirements specified in former colleagues, who have building regulations, British suggested material for this book or Standards and codes of practice, and commented on drafts, or both, we offer the published recommendations of our thanks: authoritative organisations. A defect – R B Bonshor, Lesley Bonshor, a shortfall in performance – is the R Cox, Maggie Davidson, product of a fault, but while such a R M C Driscoll, Hilary Graves, consequence cannot always be J Griggs, M S T Lillywhite, predicted with certainty, all faults have Dr R Orsler, C R Scivyer, J Seller and the potential for leading to defects. E Suttie, all of the Building Research The word failure has occasionally Establishment. been used to signify more serious We are particularly grateful to defects and catastrophes. Richard Driscoll, who contributed Where ‘investigator’ has been used, much of Chapters 1.1 to 1.3, 1.5, and it covers a variety of roles including a the majority of Chapter 2; to Ron and member of BRE’s Advisory Service, a Lesley Bonshor who prepared BRE researcher or a consultant historical and other material on working under contract to BRE. foundations and geotechnics, and on Particular terms relating to topics cracking; to Mike Lillywhite who under discussion will be found in the prepared some of the historical studies various chapters which follow. on foul drainage upon which we have drawn; and to John Ramsay, Member of The Landscape Institute, who commented on Chapters 1.4 and 1.5 from the point of view of the landscape architect, and also contributed much of Chapter 6.2.

HWH PMT December 2001 109 Chapter 2.2 Old brick and stone footings

Before the introduction of concrete Local authority byelaws in the last Main performance strip foundations for masonry walls, it years of the nineteenth century was common practice to provide required the course above the concrete requirements and defects masonry footings wider than the wall to be twice the width of the wall to be Strength and stability above in order to spread the imposed carried, with successive courses above There is an important difference load on the soil. Where the ground that reducing by quarter brick width between the behaviour of brickwork was of poor bearing capacity, with each side until the required thickness built in lime mortar, and brickwork high water tables leading to boggy of wall was achieved. In modern built in cement mortar. Masonry areas, there may even have been construction, this stepped profile has footings which used lime mortars are brushwood faggots or fascines placed been dispensed with as a simple mass much more tolerant of movement than beneath the footings in the hope of concrete strip adequately distributes are those built with cement mortars, improving bearing capacity. the load. the ductile nature of the lime mortar As well as describing the lower allowing the bricks to move slightly courses of corbelled brickwork, this relative to each other when under chapter deals with masonry below stress. In consequence, footings of DPC level – particularly its durability. buildings built before the 1930s, before lime mortars began to be superseded by cement mortars, are Characteristic details much less likely to crack when the soils on which they are founded shrink Basic description or heave. In Georgian and Victorian times the foundations of small buildings tended to be very shallow in depth, often no more than half a dozen or so courses of bricks. This brickwork below ground level was often stepped in order to spread the load, as shown in Figure 2.24. Before the widespread introduction of concrete in footings towards the end of the nineteenth century, unless the walls were founded on rock, progressively wider courses of bonded masonry were absolutely necessary to spread loads over adequate widths of subsoil. It was common practice to use as many bricks as possible laid as headers, that is to say, normal to the line of the wall so that the corbelling action was maximised. Where the wall was of stone, the same principle would apply, Firm ground with the maximum use of through Figure 2.24 Maximum use of brick stones (Figure 2.25). headers in footings gives the best Figure 2.25 Typical stone footings widely loadbearing qualities used until the end of the nineteenth century 110 2 Foundations

Where alterations are to be made to salts are transported by water to the an old building, it is crucial to expose interior of the brick and can derive and measure any masonry footings, from the external environment or from and to carry out an assessment of the the rehydration of the soluble phase of loadbearing capacity of the soil on the brick. The most deleterious salts which they are carried (Figure 2.26). are those that are readily hydratable (eg sulfates of sodium and calcium). Durability The site of crystallisation is It should be noted that discussion of determined by the dynamic balance this topic in this chapter applies only between the rate of evaporation of to those materials used below ground water from the brick surface and the level. Different considerations apply rate of solute migration to the site of to materials used above ground level, crystal growth. If the rate of solute and reference should be made to the migration is faster then the rate of appropriate parts of Walls, windows evaporation, then crystallisation and doors (101). occurs on the surface of the brick Only a few influences are known to (efflorescence). Although reduce the normally indefinite life of efflorescence is unsightly it is not materials recommended for harmful. If the rate of solute migration Figure 2.26 A narrow diameter hole has construction of foundations, the most is slow, or if the salt is relatively been excavated in a confined space significant of these being sulfate insoluble, crystallisation will take alongside a one brick solid external wall to attack and frost. Mortar for brick and place within the pores of the brick. establish the depth and width of what blockwork can have very variable This is usually referred to as sub- turned out to be brick footings. Both depth durability. Breakdown may be florescence or cryptoflorescence, and and width had to be established by probing hastened by the use of unsuitable, it can result in delamination, flaking with a long crowbar. The footings were on poor quality or incorrectly prepared and spalling(77). shrinkable clay, and were unusually deep materials. The relevant codes give A more detailed explanation of the for an Edwardian house. Tree roots are extensive guidance on the preferred effect of crystallisation of visible in the sides of the excavation specifications for given soluble salts on clay bricks is to be circumstances. Local building control found in Chapter 2.2 of Walls, departments should have information windows and doors. on the presence of aggressive soil or groundwater in particular areas. Calcium silicate bricks Where any doubts exist, samples Calcium silicate bricks are resistant to should be taken for analysis. attack by most sulfate salts in the soil Washing out mortar from footings and groundwater. The durability of or fines from the ground beneath calcium silicate bricks under salt foundations can result from leaking crystallisation attack can be attributed water mains or drains. to a combination of their very low soluble salt content, and their low Clay bricks porosity and coarse pore structure. So far as the bricks themselves are However, calcium silicate bricks may concerned, there is a wide range of be attacked by high concentrations of performance. Engineering bricks are magnesium and ammonium sulfate. highly durable, the inherently good They may also suffer severe resistance of these materials being due deterioration if they are impregnated principally to their low porosity. The by strong salt solutions, such as deterioration of brick depends on the calcium chloride or sodium chloride, nature of the contamination to which it and then subjected to frost(77). is exposed, and can occur as a result of either a chemical interaction with the Figure 2.27 A variety of contaminants ceramic materials – leading to the has obviously been in contact with this dissolution of the glassy phase, which 100 year old clay brickwork below DPC in some cases can constitute as much level, but only minor damage has resulted. as 60% of the brick – or a physical There is also evidence of previous expansion mechanism due to the alterations and some repointing crystallisation of salts within the brick pores(77); this is potentially a more serious problem (Figure 2.27). The

BRE Building Elements Building services

Performance, diagnosis, maintenance, repair and the avoidance of defects

H W Harrison, ISO, Dip Arch, RIBA

P M Trotman

BRE Garston Watford

WD2 7JR iii Contents

Preface v Readership v Scope of the book v Some important definitions vi Acknowledgements vii Some less common technical abbreviations viii 0 Introduction 1 Records of failures and faults in buildings 1 BRE Defects Database records 1 BRE publications on building services 6 Changes in construction practice over the years 6 Summary of main changes in common practice since the 1950s 10 1 Building physics (services) 17 1.1 The building as a whole 18 1.2 Energy, heat transfer and thermal comfort 21 1.3 Condensation 29 1.4 Artificial lighting 34 2 Space heating and cooling 43 2.1 Solid fuel, open fires and stoves 46 2.2 Boilers and hot water radiator systems 58 2.3 Floor and ceiling heating, and electric storage radiators 77 2.4 Warm air systems and air conditioning 80 2.5 Geothermal and heat pumps 91 2.6 Solar energy 93 3 Ventilation and ducted services 99 3.1 Natural ventilation, through windows, trickle vents and airbricks 101 3.2 Natural ventilation, passive stack 119 3.3 Forced air mechanical systems 125 iv Contents

4 Piped services 133 4.1 Cold water supply and distribution 134 4.2 Domestic hot water services 145 4.3 Sanitary fittings 155 4.4 Above ground drainage 167 4.5 Fire protection 182 4.6 Gas, including storage of LPG 189 4.7 Refuse disposal 192 5 Wired services 197 5.1 Electricity 198 5.2 Telephone, radio, TV and computer 210 5.3 Security and fire detection systems 216 5.4 Rooms for speech and sound reinforcement systems 221 6 Mechanical handling devices 229 6.1 Passenger and goods lifts, escalators and dumb waiters 230 6.2 Goods handling devices, conveyors and warehouse storage 240 References and further reading 245 Index 257 v Preface

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+:+ 307 -XO\ 17 Chapter 1 Building physics (services)

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Integration of building services Tanks and feeds Communications Ductwork and trunking into the overall design process $OWKRXJKLWPLJKWEHWKRXJKWWKDW VHUYLFHVZRXOGDOZD\VEHIXOO\ Pipework LQWHJUDWHGLQWRWKHFDUFDVVHVRI EXLOGLQJVIURPWKHVWDUWRIWKHGHVLJQ Sprinklers SURFHVVZLWKFRRUGLQDWLRQSURFHHGLQJ WKURXJKWRWKHVLWHDVVHPEO\LWLVRQO\ ZLWKLQUHFHQW\HDUVWKDWVLJQLILFDQW SURJUHVVKDVEHHQPDGH:KHQ EXLOGLQJVZHUHVLPSOHDQGKDGIHZ VHUYLFHVRWKHUWKDQSURYLVLRQIRU VSDFHKHDWLQJDKDQGSXPSLQWKH NLWFKHQDQGEHOOZLUHVWRVXPPRQWKH VHUYDQWVFRRUGLQDWLRQRIWKH Electrical supply LQVWDOODWLRQVZDVUHODWLYHO\ XQLPSRUWDQWDQGFRXOGEH DFFRPPRGDWHGSLHFHPHDO6RPHZHUH OHIWH[SRVHGLQDQ\FDVH Radiators or convectors Boilers and air heating Figure 1.3 A schematic illustration adapted from Designing for production (31) showing some of the environmental services for a large building About the authors

Peter Trotman served a student apprenticeship with Bristol Aero-Engines Ltd (now Rolls- Royce Ltd), qualifying as a mechanical and structural engineer. He was involved with the provision of facilities for ground running of aero engines. Peter joined BRE in 1967 and spent five years in the Public Health Engineering Section, carrying out research into water services and drainage. He has served on BSI committees dealing with waterproofing of below-ground structures and was a founder member of the Basement Development Group. In 1975 he joined the BRE Advisory Service, and became its Head in 1990, managing programmes of site investigations, lecturing to construction professionals and preparing

BRE technical publications. More recently he has become Co-ordinator for the CIB, Understanding dampness International Council for Research and Innovation in Building and Construction, Commission W86 – Building Pathology. Understanding Chris Sanders graduated in physics and meteorology in 1973 and worked for BRE in Scotland for 29 years, initially on the risk of condensation and mould in houses and roofs and the assessment of the effects of moulds and mites on health. He carried out the analysis of the condensation and mould data in four English House Condition Surveys. He dampness has produced guidance documents giving advice on avoiding thermal bridging in housing and other buildings and carried out the thermal analysis of the Robust Details that were produced in association with Approved Document L1 of the English Building Regulations. He is Convenor of the CEN Working Groups developing European standards on moisture and Peter Trotman climatic data and chairman of the BSI committee revising BS 5250, the code of practice for Chris Sanders condensation in buildings. He was actively involved with the UK Climate Impacts Programme and the BRE programme investigating the effects of climate change on future buildings and Harry Harrison developing cost effective measures for the repair of housing after flooding. Chris left BRE in August 2003 to become the director of the newly established Centre for Research on Indoor Climate and Health at Glasgow Caledonian University.

H W (Harry) Harrison is an architect. After short periods with a large UK building contractor and a small architectural practice, he joined BRE. He retired 34 years later as Head of Construction Practice Division. At BRE he carried out research into many aspects of the design and specification of buildings and building components, especially of weathertightness, accuracy and jointing. He has served on British and International

Standards Committees responsible for putting into practice the results of BRE and other HW research, and for several years was the secretary of Commission W60, the Performance Concept in Building, of the International Council for Building Research, Studies and

Documentation (now the International Council for Research and Innovation in Building and Trotman M and P Harrison Construction). He was a founder member of the International Modular Group. In later years he became a specialist in building defects, and was responsible for the Housing Defects Prevention Unit and the BRE Advisory Service. In the 1990 Queen’s Birthday Honours he was appointed a Companion of the Imperial Service Order for services to building research.

BRE Bookshop, Building Research Establishment, Watford WD25 9XX Tel: 01923 664761 Fax: 01923 662477 email: [email protected]

BR 466 Understanding dampness Effects, causes, diagnosis and remedies

Peter Trotman, Chris Sanders and Harry Harrison

constructing the future Contents

A complete list of contents starts on page 212 Preface Readership vii Scope of the book vii Some important definitions viii Acknowledgements viii

1 Introduction What is dampness? 1 Types of dampness 1 Condensation 2 Rain penetration 2 Rising damp 3 Construction moisture 3 Leaking pipes 3 Leaks at roofing features and abutments 3 Spills 4 Ground and surface water 4 Contaminating salts 4 Where is dampness apparent? 4 Records of dampness -related problems in buildings 5 BRE Advisory Service records 5 BRE Defects database records 6 House Condition Surveys 6 Changes lifestyle and construction 10 Changes in domestic lifestyles 10 Changes in external walling practice 10 Changes in floor construction practice 11 Changes in roof construction practice 12 Changes in levels of risk 13 BRE publications on dampness 13

2Visible and hidden effects of dampness Health effects of mould and damp 15 Mould problems and health 15 Diagnosis 18 Surveys 18 Staining 18 Visible moisture 18 Condensation 18 Rain penetration 19 Rising damp 19 Mould growth 20 Surface moulds 20 Algae, lichens and mosses 21 Toxic mould 21 Remedies 21 Salts 23 Diagnosis 23 Remedies 23 Frost 23 Diagnosis 23 Remedies 25 Timber rot 25 Types of fungi 25 Occurrence of rot 25

iii Understanding dampness

Remedies 26 Metal corrosion 28 Parts of the building at risk 28 Diagnosis 32 Remedies 34 Hidden dampness 36 Diagnosis 36

3Measuring moisture Instruments for measuring moisture 39 Sampling 39 Electricalresistance moisture meters 40 Resistance gauges 42 Microwave techniques 42 Capacitance methods 43 Physical sampling by independent cores 43 Drilled samples 43 Moisture contents at which action may be required 46 Laboratory tests for salts 47 Procedure 47 Typical salts contents 48 Instruments for measuring the humidity 48 Thermohydrograph 48 Electronic sensors 49 Wet bulb and dry bulb thermometers 49 Dewpoint sensors 49

4 Condensation Water vapour 51 Behaviour of water vapour in the air 51 Production of water vapour within buildings 54 Effects of condensation 55 Condensate on surfaces 55 Mould growth 55 Design to control condensation 59 Interstitial condensation 59 Effects of interstitial condensation 60 Controlling interstitial condensation 61 Vapour control layers 62 Construction 62 Joints 62 Performance 62 Hygroscopic materials 63 Materials affected 63 Reverse condensation 63 Incidence of condensation 64 Case studies of surface condensation 64 On walls 64 On windows and doors 65 In roofs 65 On floors 67 Investigating and curing condensation 69 Measuring temperature and humidity by data-loggers 69 Diagnosis 69 Case studies 72 Condensation in a terraced bungalow with ceiling heating 72 Water dripping from the ceiling in a fine-art store room 74 Condensation in an infants’ school 76 Condensation in steel-framed houses 78

iv 5 Rain penetration Driving rain 84 Wind-driven snow 85 Driving Rain Index 85 Protection given by overhangs 85 Rain penetration in walls 91 The mechanisms 91 Run-off 92 Solid walls 95 Masonry cavity walls 98 Panelled walls 100 Curtain walling 102 Timber frame walls 104 Survey methods 105 Diagnosis 105 Remedies – external 105 Remedies – internal 109 Workmanship 110 Damp-proof courses 111 Rain penetration at openings 116 Windows 116 The window-to-wall joint 116 Doors and thresholds 119 Rain penetration in roofs 122 Pitched tiled and slated roofs 122 Incidence of defects 127 Diagnosis 130 Other pitched roofs 130 Patent glazing 133 Flat and low pitch asphalt and bituminous felt roofs 134 Bays and porches 140 Chimneys 140 Case studies 142 Water dripping from a bakery roof 142 Rain penetration at a medieval church 144 Water ingress through a solid brick parapet 145 Rain penetration in a Victorian stately home 146

6 Rising damp and groundwater movement The theory 150 Saturated ground 150 Soluble salts 150 Rainfall splashing 151 Diagnosis 151 Failures of existing DPCs 151 Range of possibilities 152 Using an electrical moisture meter 153 Drilled samples 154 Rising damp in walls 155 The problem 155 Earth, clay and chalk walls 155 Solid masonry walls 155 Cavity masonry walls 156 Materials for DPMs and DPCs 157 New build 158 Treatment 158 The choice of DPCs 158 Replastering as a solution 162 Dry lining 162

v Understanding dampness

Monitoring of the behaviour of a replacement DPC 163 Replastering following a new DPC 163 Impervious linings 164 Floors 164 The problem 164 Characteristics of failure 165 Sources of moisture 165 Excluding rising damp 169 Materials for DPMs 176 Volatile organic compounds 177 Waterproofness of floorings 179 Groundwater and basements 182 The problem 182 Level of protection required 183 Waterstops 184 Converting basements during rehabilitation 185 Curing dampness problems 186 Drained cavity 187 Mastic asphalt tanking 187 Cementitious render or compound 188 Self-adhesive membranes 188 Liquid-applied membranes 188 Ventilated dry lining 189 Partition walls 189 Basement ceiling level 189 Door thresholds 190 Door and window frames 190 Fixing services 190 Chimney breasts 190 Built-in timbers 190 Case studies 191 Dampness in internal walls in a converted stable block 191 Severe damp and related problems in N0-fines houses 192 Moisture in chipboard flooring over foamed polystyrene 194 Dampness from leaking pipes in commercial properties 196 Damp in a listed building 198 Soluble salts in the Tower of London 200

7 More about dampness Construction water and drying out 203 Entrapped water 203 Surface DPMs 205 Flooding 205 Immediate action 205 Inspections 207 Remedies 207 Spills and leaks 209 Contaminated materials: sources and treatment 210 Animal residues 210 Chimneys 210 Storage of salts 210

Complete list of contents 212 References and further reading - a complete list 215

vi Preface

Many years ago, before the Building Research Station was founded, the British Medical Association asked the Royal Institute of British Architects to investigate the causes of dampness in dwelling houses to help them find the reasons for the prevalence of certain diseases. The RIBA committee found that direct penetration of rain through walls and lack of a damp-proof course (DPC) accounted for nearly two-thirds of all cases; condensation contributed only 2%. The causes may have since changed in relative importance with changes in construction techniques, such as cavity walls and the tendency for houses to be better heated. Unfortunately, though, dampness is a continuing source of distress to occupants. It is possibly a source or a contributor to illness, it encourages deterioration in the building fabric, and it is involved in half of the investigations undertaken over the years by BRE.

As well as damp patches on walls, ceilings and floors, dampness can lead to blistering paint, bulging plaster, rot in building timbers, mould on surfaces and fabrics, and sulfate attack on brickwork. It can also lead to less visible problems, such as reduced effectiveness of thermal insulation or cracking in brickwork as a result of corrosion of embedded metal components. Despite all the technical advice that has been published in the past, there is still a significant set of problems. This book seeks to address them.

Readership This book is aimed primarily at all professionals involved in the design, maintenance and management of domestic, public, commercial and industrial properties; this includes surveyors, architects, builders and facilities managers. It will also be useful to student members of these professions. Much of the text and many of the illustrations will also be of relevance to householders and other users of buildings.

Scope of the book The emphasis of this book is on existing buildings with some coverage of the design of new build. It lists the causes of dampness in buildings and explores the consequential effects of that dampness on the fabric, the maintenance of protection against dampness, and the remedies which the detrimental results of dampness will call for.

It is illustrated with photographs of defects from the BRE Advisory Service collection and drawings of construction elements that need careful design and execution. Case studies illustrate some of the more typical problems which have been investigated as well as some interesting but informative non- typical cases, although it must be recognised that it is rare to find two cases which are identical in every detail.

Chapter 1 contains background information. Chapter 2 provides a visual indication of the most common manifestations of dampness to be seen in buildings, tabulated according to building element. When the appearance of the defect under investigation has been matched with the appropriate photograph, a key provides a link to later chapters which give explanations of the physics, further information to confirm the diagnosis, and the remedies which might be specified to put right the defect.

Although this book is mainly about existing buildings, and not specifically about the design of new buildings, it gives some design criteria so that subsequent performance of the completed building may be assessed against what was either required or intended.

vii Understanding dampness

Some important definitions Condensation: the process whereby water is deposited from air containing water vapour when its temperature drops to or below the dewpoint.

Dampness: used here to cover a wide variety of phenomena relating to the unwanted presence of water or water vapour, whatever its cause.

Deliquescent substance: substance which becomes damp and finally liquifies on exposure to the atmosphere, owing to the low vapour pressure of its saturated solution.

Dewpoint temperature of the air: the temperature at which condensation of liquid water starts when air is cooled, at constant vapour pressure.

Hygroscopic substance: usually applied to solids which tend to absorb moisture from the atmosphere without actually becoming liquified.

Psychrometric: Relating to the measurement of water vapour in the air, including the use of the wet and dry bulb hygrometer.

Rain penetration of walls and roofs: results from water entering the structure to such an extent that the resulting dampness or dripping of water becomes a nuisance.

Relative humidity: the ratio, normally expressed as a percentage, of the actual amount of water vapour present to the amount that would be present if the air were saturated at the same temperature.

Reverse condensation (old term: summer condensation): interstitial condensation that can occur when moisture within a wall is driven in by solar radiation on south-facing walls.

Rising damp: normally the upward transfer of moisture in a porous material due to capillary action.

Thermal bridge (old term: cold bridge): part of a structure of lower thermal resistance which bridges adjacent parts of higher thermal resistance and which can result in localised cold surfaces on which condensation, mould growth and/or pattern staining can occur.

Vapour control layer (VCL): usually a thin sheet material with a vapour resistance greater than 200 MNs/g, used on the warm side of thermal insulation to restrict moisture which diffuses through the insulation from condensing on any colder outer surface.

Acknowledgements Unless otherwise attributed, photographs have been provided from our own collections or from the BRE Photographic Archive, a unique collection dating from the early 1920s.

We offer our thanks to the following colleagues and former colleagues who have suggested material for this book or commented on drafts, or both: Phil Cornish Stephen Garvin Colin Hunter Tony Roberts Charles Stirling Tim Yates

PMT CHS HWH April 2004

viii Chapter 5 Rain penetration

Driving rain and the driving rain index Rain penetration in walls Rain penetration at openings Rain penetration in roofs

This chapter tells you how to assess the risk of specific designs in actual locations in the UK using the driving rain index, and deals with rain penetration in solid and cavity masonry walls, cavity wall insulation, cladding systems, DPC detailing principles and well-tried details, rain penetration of pitched and flat roofs, parapets and leaking windows.

Figure 5.1 A disfiguring deposit of carbonate from rain penetrating the sloping brickwork parapet

Figure 5.2 Although much of this results from condensation, there is also some rain penetration

83 Understanding dampness

There are regional construction differences throughout the UK as a result of local experience and practice as well as available materials. In more exposed locations, walls may be sand:cement rendered and slate or tile- hung in Cornwall and Scotland. Pitched roofs are given a second line of defence with a sarking material of felt or plastics. In Scotland, boarding is used as the sarking. Windows in Scotland are usually inset to give protection; other parts of the UK use a narrow sill with the window much closer to the line of the outer leaf.

DRIVING RAIN In the Building Regulations, control of moisture is a functional requirement and the building must be designed to adequately resist such penetration – see Approved Document Part C and Part G.

An International Council for Research and Innovation in Building and Construction (CIB) Working Commission on Rain Penetration meeting in the 1950s adopted a definition of rain penetration: By rain penetration is meant that rainwater penetrates into a wall either through the surface of the wall, or due to leakage at windows or similar installations. It is not necessary that water penetrates so far that it may be discernible on the inside of the wall. More information is in Rain Penetration Investigations - A summary of the findings of CIB Working Commission on Rain Penetration - Oslo 1963.

Rain penetration in modern cavity walls tends to show as a well-defined roughly circular area on internal finishes. Sometimes surface salts will define the outer limits of such wetting. If the wetting persists, most of the wall may become visibly damp. In older, solid wall buildings, wetting may not be visible because successive coats of emulsion paint or vinyl wallpaper have masked the effects. The extent of the dampness, or if dry the salts which define it, can be traced with a moisture meter.

Moisture can be deposited on external surfaces in several ways: ❐ Gentle rain or drizzle normally falls vertically and will accumulate on flat surfaces. Some splashing may wet adjacent surfaces. ❐ Driving rain, which is heavy rain blown by a strong wind on to horizontal and vertical surfaces. Water can also be blown uphill on sloping surfaces. ❐ Snowfall and wind-blown snowdrifts have little effect at the time but when the snow melts, it can cause severe wetting, particularly very fine snow blown into pitched roofs. ❐ Fog wets external surfaces but in small quantities and has little effect. ❐ Condensation can occur on outside surfaces in tropical climates, particularly with air-conditioned buildings. Storms in these climates are more likely to be a test of weathertightness. Figure 5.3 Severe wetting from driving rain on an exposed wall

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