BRE BUILDINGS DESING, Apuntes de Ingeniería Civil

¡Descarga BRE BUILDINGS DESING y más Apuntes en PDF de Ingeniería Civil solo en Docsity! 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 A cv. bre PREFACE TO THE THIRD EDITION The third edition of this book is being published at a time when the UK construction industry is facing a significant reduction in its work load, and nearly a decade after the second edition was prepared. That decade has seen massive changes in public awareness of the need for sustainability in construction, and the introduction of the Code for Sustainable Homes in November 2006, which since May 2008 has formed a basis for assessment of the acceptability of the design of new housing in England and Wales. But similar needs exist for the whole of the UK's future building programme, new-build hospitals, factories, educational buildings and other long-life buildings which will provide challenges to designers in meeting the conditions brought about by anticipated climate changes and the need to be carbon-neutral and to conserve our dwindling natural resources. There have also been significant changes in British Standards which increasingly reflect those taking place in Europe. However, the UK cannot afford year-on-year to renew more than a very small percentage of the stock of existing buildings, and the need for intelligent conservation and upgrading of the old stock is arguably of equal if not more importance. Itis against this background that this third edition of Roofs and roofing has been prepared. In addition to thorough revision of the chapters on the more traditional forms of construction, such as tiling and slating, completely new chapters have been prepared on: + extensive lightweight green roofs, + modern methods of construction, * roof-mounted photovoltaic systems, + thermal insulation in lofts, + loft conversions, + single-layer membranes. New sections have been introduced as appropriate into existing chapters, including: + new:forms of metal roofing, + siphonic roof drainage, * new materials technologies, + improved protective finishes for timber, metals and concrete. Where appropriate, each chapter now contains a section dealing with provisions that may become necessary to accommodate climate change (eg increased rainfall, stronger winds and higher temperatures). There have been considerable changes too in the standards covering roof drainage which have been reflected in the revised text. Approximately one-quarter of the photographs are new to this edition. HWwH PMT GKS June 2009 3 SHORTSPAN DOMESTIC PITCHED ROOFS. | 77| 3 SHORT-SPAN DOMESTIC PITCHED ROOFS Short=span roofs are normally defined as being of less than 8-9 m span. Pitched roofs are conventionally defined as those roofs with slopes greater than 10%, whereas roofs of slope 10? or less are defined as flat. For the purposes of this book, pitched roofs have been categorised into those covered in relatively small overlapping units, dealt with in Chapters 3.1, 3.2 and 3.6, those covered in sheet materials, dealt with in Chapters 3.3-3.5, and thatch, which forms a category of its own, dealt with in Chapter 3.7. Small overlapping units consist of the following types: + dlay tile, + concrete tile, + natural slate, * manmade slate, + shingles. Figure 3.2 shows the current market share held by the first four categories. Following increased appreciation of the need to protect the environment, there has been limited use of recyded materials such as rubber. The increased popularity of PV systems is envisaged which will affect the type of roofing chosen to support them. Some general information about defects in pitched roofs in housing can be found in Assessing traditional housing for rehabilitation". Fibre-cement products 7% Clay tiles 12% Concrete tiles 61% Figure 3.2: Roof tile market by value, 2006. Data from Roofing Market Report" Figure 3.1 This steeply pitched plain tiled roof was built in 1880 but re-covered after bomb damage in the 1939-45 war E US Using Figure 3.25, the effective catchment area that will discharge to each gutter is: + for the slope of a pitched roof, the plan area, A (m3), plus half the elevation area, B| (mí) (Figure 3.25), + fora pitched roof abutting a wall, the plan area, A, plus half the elevation area, B, plus half the wall area, C, above the roof slope (Figure 3.25b), + fora flat roof, the relevant plan area. The run-off rate to each gutter is the total catchment area for the gutter divided by 48. This produces the run-off in litres per second using the recommended rainfall (thunderstorm) rate of 75 mm/hour. The size of the guttering is shown in Table 3.5 using the flow capacity that will accommodate the run-off rate. As part of this process, the number of outlets should be considered: more outlets from a run of guttering spreads the total loading on the gutter, but the loadings will vary according to where the outlets are positioned (Figure 3.26). (a) This gutter needs to have twice the flow capacity of... - .. this gutter, “and four times the Figure 3.25: Catchment areas for capacity of... calculating rainwater run-off TN] standard eaves gutters (when level) Flow capacity Size of (litres/sec) gutter True Nominal (mm) half round half round 75 0.38 0.27 100 115 EE 1 I - this gutter, 150 Figure 3.26: Spacing between outlets to reduce water load on gutters 3. SHORTSPAN DOMESTIC PITCHED ROOFS Ma BRE site inspections. Drawings have been seen that specifically state that the design of gutter systems should be left to the site staff to sort out! The pitch of valley gutters is less than the pitch of the roof they join, and valley gutters on pitches of less than 20” are particularly prone to leaking. Poor detailing was commonly found in the BRE quality assessments. BRE site inspections revealed a number of cases where gutters had not been installed on porches and bay windows: decisions which may be marginal where the drips cause no inconvenience to the occupants, but less acceptable for doorways (Figure 3.27). A room in the roof Where a room is formed within 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! and 1191 deal with this problem, particularly where it involves the careful placing of thermal insulation to ensure an adequate ventilation gap. Thermal insulation: avoiding risks*4l is also helpful. The most important points to watch are: + thata vapour control layer (eg of at least 500-gauge polyethylene) is installed in the sloping part of the roof under the insulation, + thata vapour permeable sarking is used in new construction, + that cupboards should be within the insulated envelope, ensuring continuity of the lining. MAIN PERFORMANCE REQUIREMENTS AND DEFECTS Choice of materials for structure Timber has been used as the main structural material in the vast majority of tiled roofs: those dating from before the early 1960s for the most part designed with strutted purlins (Figure 3.29), more recent designs using trussed rafters. The structure of most of these is in good condition (only 1 in 8 of these structures being reported as faulty!%), provided attention has been paid to routine maintenance of the covering. 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 andresistance 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 atthe 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 Insituterrazzo 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 semiflexible 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 Howto choose a flooring 284 References and further or general reading 285 Index 295 First edition It has been said that most problems with floors occur because people insist on walking on them, pushing trolleys over them, placing large objects on them and dropping things on them - ifonly they were ceilings they would never wear out! A small witticism that reflects the way some people, including professionals in the construction industry, see floors. Or, rather, don't see them! After all, what is there to a floor: floorboards nailed to joists. What can go wrong with that? And ifit happens to form a ceiling, even better. But the facts belie this perception. BRE's figures on faults in buildings ofall types (givenin greater detail in the introductory chapter which follows) show that a substantial number concern floors. Despite the advice that has been available to the industry from the 19205, faults in flooring, such as cracking, detachment and entrapped water, recur frequently. Ifsome of the errors appear elementary, this only reflects what happens in the design office and on site. All that we can do is show to those who work in the flooring industry what is being done incorrectly and how to take corrective action — preferably before faults or defects lead to costly damage. This book describes the materials and products, methods and criteria which are used in the construction of floors and flooring. It draws the reader's attention to those elements and practices which ensure good performance or lead to faults and failure. There is sufficient discussion Preface of the underlying structure to enable an understanding of the behaviour of the whole floor without going very far into engineering design principles. It does not purport, though, to be a book of construction practice; nor does it provide the reader with the information necessary to design a floor, but, mainly through lists and comprehensive illustration, shows him or her what to look for as good and bad features of floors and flooring. It also offers sources of further information and advice. Readership Floors and flooringis addressed primarily to building surveyors and other professionals performing similar functions, such as architects and builders, who maintain, repair, extend and renew the national building stock. Lecturers and other educators in the building field will also find it to be a useful adjunct to their course material. Scope of the book Although books on flooring are few, there is no shortage ofindustry guidance on floors and flooring. The problem is that people do not use the guidance that exists. To try to remedy that situation, the contents of this book are configured so that the principles, features and functions of floors and flooring are described first (Chapter 1). There needs to be sufficient discussion of principles to impart understanding of the reason for certain practices; without that understanding, practitioners will have difficulty following correct procedures - oruntil they make the mistakes, or overlook precautions, as previous generations have done. The criteria presented in Chapter 1 are then related to the different types offloors and their finishes (Chapters 2-8). The text concentrates on those aspects of construction which, in the experience of BRE, lead to the greatest number of problems or greatest potential expense if carried out unsatisfactorily. It follows that these problems will be picked up most frequently by maintenance surveyors and others carrying out remedial work on floors. Although most of the information relates to older buildings, surveyors may be called upon to inspect buildings built in relatively recent years. It is therefore appropriate also to include much material concerning observations by BRE ofnew buildings under construction in the period 1985-95. Many of the difficulties which are referred to BRE for advice stem from too hasty assumptions about the causes of particular defects. Very often the symptoms are treated, not the causes, and the defects recur. It is to be hoped that this book will encourage a systematic approach to the diagnosis of floor and flooring defects. The case studies provided in some of the chapters are selected from the files ofBRE Advisory Service and the former Housing Defects Prevention Unit, and represent the most frequent kinds of problems on which BRE is consulted. They are not meant to be comprehensive in scope since the factors affecting 56 1 The basic functions of all floors Chapter 1.9 Figure 1.60 The durability of any flooringis governed ultimately by the kind of use it gets, particularly by heavy wheeled vehicles 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 ona particular surface, will be given in the appropriate later chapter. Floor finishes may be considered to provide for the following main functions: e protection ofthe structural floor 0 better appearance e increased comfort and safety The relative importance of these functions varies according to circumstances and budgets. However, one ofthe mostimportant attributes is the maintenance of the functions over time; in other words, the finishes must be durable. Because ofits importance, durability has often been regarded as a basic property of a floor finish, but it represents only the length of time that the chosen properties persist and depends as much on the conditions ofuse as on the properties ofthe finish, Many factors influence the life of afloor finish: O wear 6 water and other liquids e indenting loads and impacts (Figure 1.61) 0 sunlight 0 insects e moulds and fungi e high temperature as well as the fundamental properties of the materials and adhesives used, and the compatibility ofthese with other parts of the structure and its behaviour in use. Figure 1.61 This industrial floor has suffered very heavy wear in spite of the robust finish. lt has been subjected to piecemeal replacement. The wheel tracks of mechanical handling equipment can be seen The European Union of Agrément (UEAtc) have given priority, in their Method of Assessment and Test covering innovative floorings, to assessing the conditions of service for floorings using what has been called the UPEC system. UPEC is the French acronym for wear (usure) index 1-4, indentation (poingonnement) index 1-3, water (eau) index 0-3, and chemicals (chimiques) index 0-3 (UEAte Method of Assessment and Test No 20”). Given the existence of an Agrément certificate fora particular product, therefore, a surveyor should be able to make a judgement on its performance. UEAtcand the British Board of Agrément (BBA) have also issued further guidance on the assessment 1.9 Durability 57 Figure 1.62 This paint finish is breaking up. There is little substance to resist further wear of plastics floorings (UEAte Methods of Assessment and Test No 23% and No 36%, and BBA Information Sheet No 2%). These are referred to in greater detail in the appropriate later chapters. Experience has shown that there is a relationship between wear and indentation ofPVC floorings; these floorings, invariably, havea C index of2. For PVC floorings, it has therefore been found possible to omit the C rating, and to combine the U and P ratings into a single G classification (1-5). Ofall the performance factors described above, wear is perhaps the most influential because: € itis unavoidable in normal use e itapplies to all kinds of flooring 6 ¡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), 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 ofa floor covering depends as much on the conditions in the building and the degree ofuse as on the inherent properties ofthe 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 reasonable expectation ofa minimum service life for a properly selected flooring, taking all circumstances into account. What that minimum might be isa matter for debate, but UEAtc have decided on 10 years, and BRE would not dispute that figure”. Durability is affected by the care and skill with which the floor is laid, and the behaviour ofthe subfloor, as well as by the choice of material itself. Failure to provide adequate dampproofing and ventilation, and a sound screed, can lead to serious deterioration in finish; for example as buckling of wood block floors or loss of adhesion in tiled or painted finishes (Figure 1.62). Resistance to wear All floor surfaces wear to some degree when subjected to foot or wheeled traffic. There may also be other factors including the movement of furniture, which may scrape or cut the surface, and the movement of heavy loads such asin warehouses. However, usingthe definition of wear as the progressive loss from the surface ofa body brought about by mechanical action, it is not just the quantitative loss of material which is important but also the qualitative assessment of the condition of the worn surface. Where changes in appearance are Figure 1.63 Measuring the forces applied by foot traffic to flooring. Although these tests were conducted in the late 1950s, the results still apply involved, the assessment becomes more and more subjective. Wear and damage can be considered to arise from a number of causes: e mechanical action (leadingto progressive loss of substance) e abrasion caused by fine solid particles e cutting by the action of vehicles (eg trolleys) and furniture e corrosion from spillages e degradation from soluble salts rising from the subsoil or entrapped moisture in concrete e fatigue in the surface material e movement orrocking from uneven or friable bedding causing chipping ofarrises of slabs or tiles There has been considerable concern since the 1960s with the degree of wear of floors in heritage buildings. This is dealt with in detail in Chapters 5.2 and 5.5. In some cases, depending of course on the material involved, it is evident that wear of around one millimetre in ten years is occurringÚ, ( press BRE Building Elements Walls, windows and doors H W Harrison and R C de Vekey Performance, diagnosis, maintenance, repair and the avoidance of defects NY iv Contents 3 External cladding on frames 125 3.1 Masonry on steel or concrete frame 126 3.2 Precastconcrete on steel or concrete frame 132 3.3 Timberframe 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 This book is about all the main vertical elements of buildings, both external, including walls, windows and doors, and internal, including separating walls, partitions and internal doors. It deals in outline with the achieved performances and deficiencies of the fabric over the whole age range of the national building stock. Of course, many performance requirements are common to buildings of whatever age, the main difference being that occupants tend to make allowances for deficiencies when the building isold. The construction ofa wall and its constituent materials must have adequate strength, be fire resistant, offer the necessary acoustic and thermal properties, and resist erosion and corrosion for the life of the building, so that the occupants can use the building safely and conveniently. In addition, the external envelope should have adequate resistance to the elements, and must allow the maintenance ofa suitable indoor environment. Information on faults in buildings ofall types show that nearly half concern walls, windows and doors. Despite the advice that has been available to the industry from the 1920s, faults which formerly occurred ona substantial scale, such as rain penetration through windows and doors, still recur frequently. Some of these faults may appear to be elementary in character, but this only reflects what happens in practice. Recognition of faults before they occur on site is obviously much more preferable to correction after the event. Insome Preface cases an underlying cause ¡is lack of knowledge, in others a lack of care. Readership Walls, windows and doors is addressed primarily to building surveyors and other professionals performing similar functions — such as architects and builders— who maintain, repair, extend and renew the national building stock. It will also find application in the education field. In spite of the current explosion of information, or perhaps because of it, people do not use the guidance that exists. In order to try to remedy that situation, the advice given in Chapters 2 to 10 of this book concentrates on practical details. However, there also needs to be sufficient discussion of principles to impart understanding of the reason for certain practices, and much of this information is given in Chapter 1. Scope of the book AlI kinds of external walls, encompassing loadbearing and non- loadbearing, curtain walls, and overcladding are dealt with first; then windows and external doors, including thresholds. Later chapters include separating walls, partitions, and internal doors and stair enclosures including protected shafts. In principle, all types of buildings are included, though obvious practical considerations of space decree that information on heritage buildings is limited in scope. The book is nota manual of construction practice, nor does it provide the reader with the information necessary to design a wall. Both good and bad features of walls, windows and doors and the joints between them are described, and sources of further information and advice are offered. The drawings are not working drawings but merely show either those aspects to which the particular attention of readers needs to be drawn or simply provide typical details to support text. Excluded from the scope of this book is consideration of foundations for walls, or basements, which will be dealt with in another publication. Wall-to-roof junctions at eaves and verges, and fabric or flexible plastics sheathings to buildings were dealt with in the companion book, Roo) and roofing. As with the other books in this series, the text concentrates on those aspects of construction which, in the experience of BRE, lead to the greatest number of problems or greatest potential expense, if carried out unsatisfactorily. It follows that these problems will be picked up most frequently by maintenance surveyors and others carrying out remedial work on walls, windows and doors. Occasionally there is information relating to a fault which is infrequently encountered, and about which it may in consequence be difficultto locate information. Although most of the information relates to older buildings, much material concerning observations by BRE of new buildings under construction in the period from 1985 to 1995 isalso included. Many of the difficulties which are referred to BRE for advice stem from too hasty an assumption about the causes of a particular defect. Very often the symptom is treated, not the vi Preface cause, and the defect recurs. Itis to be hoped that this book will encourage a systematic approach to the diagnosis of walls and walling defects. The case studies provided in some of the chapters are selected from the files ofthe BRE Advisory Service and the former Housing Defects Prevention Unit, and represent the most frequent kinds of problems on which BRE has been consulted. The standard headings within the chapters are repeated only where there is a need to refer the reader to earlier statements or where there is something relevant to add to what has gone before. Since it is necessary to consider the enclosures for stairways in conjunction with stair flights, enclosures for stairways (including such items as protected shafts) are therefore considered as elements of walls and are dealt with in this book in Chapter 6.3. In the United Kingdom, there are three different sets of building regulations: The Building Regulations 1991 which apply to England and Wales; The Building Standards (Scotland) Regulations 1990; and The Building Regulations (Northern Ireland) 1994. There are many common provisions between the three sets, but there are also major differences. This book has been written against the background of the building regulations for England and Wales since, although there has been an active Advisory Service for Scotland and Northern Ireland, the highest proportion of site inspections has been carried out in England and Wales. In addition, the technical aspects of the book are affected more by exposure due to location and height above sea level than by national or administrative boundaries. The fact that the majority of references to building regulations are to those for England and Wales, should not make the book inapplicable to Scotland and Northern Ireland. There is insufficient space in this book to deal with the highly sophisticated new forms of external walls, such as the so-called “smart” or intelligent skins, employing variable external fabric, to improve solar control and daylight utilisation. Itis intended that these form part ofa further book in this series. Information relating to these techniques may be sought from BRE. Some important definitions Since the book is mainly about the problems that can arise in walls, windows and doors, two words, “fault” and “defect”, need precise definition. Fault describes a departure from good practice in design or execution of design: itis used for any departure from requirements specified in building regulations, British Standards and Codes of practice, and the published recommendations of authoritative organisations. A defect— a shortfall in performance — is the product of a fault, but while such a consequence cannot always be predicted with certainty, all faults have the potential for leading to defects. The word failure has occasionally been used to signify the more serious defects (and catastrophes!). Where the term 'investigator' has been used, it covers a variety of roles including a member of BRE's Advisory Service, a BRE researcher ora consultant working under contract toBRE. Because the term “separating wall” has been used in the construction industry from the earliest days, and is still in current use, we prefer to use it in this book as a generic term despite the comparable term “compartment wall” which is found in the national building regulations. Acknowledgements Photographs which do not bear an attribution have been provided from our own collections or from the BRE Photographic Archive, a unique collection dating from the early 1920s. To the following colleagues, and former colleagues, who have suggested material for this book or commented on drafts, or both, we offer our thanks: MJ Atkins, P Bonfield, R Cox, E J Daniels, Maggie Davidson, C Grimwood, W H (Bill) Harrison, € Holland, M Howarth, Dr P Littlefair, Penny Morgan, F Nowak, DrR Orsler, M Pound, P W Pye, RE H Read, J Reid, Justine Redshaw, B Reeves, J Seller, AJ Stevens, C M Stirling, N Tinsdeall, PM Trotman, P Walton, and Dr T Yates, all ofthe BRE. We wish to acknowledge a special debt to PM Trotman for providing the majority of the information in Chapter 2.6. In addition, acknowledgement is given to the original though anonymous authors of Principles of modern building, Volume 1, from which several passages have been adapted and updated. HWH RC de V July 1998 m press BRE Building Elements Foundations, basements and external works -HW Harrison and P M Trotman AA diagnosis, maintenance, repair and the ells NA BRE WD25 9XX BRE Building Elements Foundations, basements and external works Performance, diagnosis, maintenance, repair and the avoidance of defects H Wharrison, ISO, Dip Arch, RIBA PM Trotman 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 Theeffects 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 vi Preface Foundations, basements and external works is nota manual of construction practice, nor does it provide the reader with the information necessary to design foundations, basements or external works. Both good and bad features of these elements are described, and sources of further information and advice are offered. The drawings are not working drawings but merely show either those aspects to which the particular attention of readers needs to be drawn, or simply provide typical details to support text. The discussion, for the most part, is deliberately neutral on matters of style and aesthetics and is wary of suggesting that there is ever a unique optimum solution. Ina similar fashion to the other books in this series which deal with other building elements, the present text concentrates on those aspects relating to the subject matter of the book, in this case the site, and which, in the experience of BRE, lead to the greatest number of problems or greatest potential expense if carried out unsatisfactorily. It follows that these problems will be picked up most frequently by maintenance surveyors and others specifying and carrying out remedial work. Occasionally there is information relating to an item, perhaps a fault, which is infrequently encountered, and about which it may be difficult to locate information. Although mostof the information relates to older buildings, much material concerning observations by BRE investigators of new buildings under construction in the period from 1985 to 1995 is also included. The case studies provided in some of the chapters are selected from the files ofthe BRE Advisory Service, and the former Housing Defects Prevention Unit, and represent the most frequent kinds of problems on which BRE has been consulted. The standard headings within the chapters are repeated only where there is a need to refer the reader to earlier statements or where there is something relevant to add to what has gone before. An exception to the sequence of standard headings occurs in Chapter 2.1 where the amount of material to be described requires a further breakdown into diagnosis, monitoring and remedial work. Chapter 3 also does not follow the standard headings; it was found to be more appropriate to deal separately with structure and waterproofing of basements which is reflected in the sub-chapter headings. In the United Kingdom, there are three different sets of building regulations: The Building Regulations 1991 which apply to England and Wales; The Building Standards (Scotland) Regulations 1990; and The Building Regulations (Northern Ireland) 1994. There are many common provisions between the three sets, but there are also major differences. The book has been written against the background of the building regulations for England and Wales, since, although there has been an active Advisory Service for Scotland and Northern Ireland, the highest proportion of site inspections has been carried out in England and Wales. The fact that the majority of references to building regulations are to those for England and Wales should not make the book inapplicable to Scotland and Northern Ireland. Although practically all topics relating to the construction of buildings are encompassed in the Construction (Design and Management) Regulations 1994, the ramifications for each of the topics covered in this book are quite diferent. It is therefore not practical to spell them out, beyond noting that there must be a Health and Safety Plan and File for all construction work which should include information on how to manage health and safety issues after the installation is completed and throughout its life until demolition'”. Design criteria While this book is mainly about existing buildings and not specifically about the design ofnew buildings, it has been necessary in several circumstances to give some design criteria so that subsequent performance of the completed building may be assessed against what was required or intended. Some important definitions The term “footprint” has been used to describe the area actually covered by the building fabric. Note that this term is not synonymous with the term curtilage, as used in legislation, which in its normally accepted meaning includes any ground forming a part of the enclosure within which the building stands. The term “surcharge” as used in this book has two distinct meanings: a preloading of the ground (eg to induce consolidation), and a condition in which water is held under pressure within a gravity drain, but which does notescape to cause flooding. So far as water terms are concerned, there has been a significant change in usage since the 1980s. The term “potable water” to describe water ofa quality suitable for drinking is now no longer popular though it is still contained in current Standards, and the words “drinking” and “wholesome” to describe water are preferred. The use of the term *foul water” in relation to sewage has fallen out of official use, being superseded by the term “wastewater” which is often more closely defined as *greywater” or “blackwater”; “greywater” is wastewater not containing faecal matter or urine, “blackwater” is wastewater that contains faecal matter orurine. However, for the purposes of this book, we tend to retain the term foul water when referring to greywater and blackwater; wastewater, though, can include surface water (eg run-off from car parks). The term “aerobic” indicates conditions in which free oxygen is present, and “anaerobic” in which itis not present. Preface vii Since the book is to a considerable extent about the problems that can occur in the below-ground fabric of buildings, two words, “fault and *defect”, need precise definition. Fault describes a departure from good practice in design or execution of design; itis used for any departure from requirements specified in building regulations, British Standards and codes of practice, and the published recommendations of authoritative organisations. A defect— a shortfall in performance — is the product of a fault, but while such a consequence cannot always be predicted with certainty, all faults have the potential for leading to defects. The word failure has occasionally been used to signify more serious defects and catastrophes. Where “investigator” has been used, it covers a variety of roles including a member of BRE's Advisory Service, a BRE researcher or a consultant working under contract to BRE. Particular terms relating to topics under discussion will be found in the various chapters which follow. Acknowledgements Photographs which do not bear an attribution have been provided from our own collections or from the BRE Photographic Archive, a unique collection dating from the early 1920s. To the following colleagues, and former colleagues, who have suggested material for this book or commented on drafts, or both, we offer our thanks: RB Bonshor, Lesley Bonshor, R Cox, Maggie Davidson, R MC Driscoll, Hilary Graves, J Griggs, M ST Lillywhite, DrR Orsler, CR Scivyer, J Seller and E Suttie, all of the Building Research Establishment. We are particularly grateful to Richard Driscoll, who contributed much of Chapters 1.1 to 1.3,1.5,and the majority of Chapter 2;to Ron and Lesley Bonshor who prepared historical and other material on foundations and geotechnics, and on cracking; to Mike Lillywhite who prepared some of the historical studies 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 ofthe landscape architect, and also contributed much of Chapter 6.2. HWH PMT December 2001 109 Chapter 2.2 Before the introduction of concrete strip foundations for masonry walls, it was common practice to provide masontry footings wider than the wall above in order to spread the imposed load on the soil. Where the ground was of poor bearing capacity, with high water tables leading to boggy areas, there may even have been brushwood faggots or fascines placed beneath the footings in the hope of improving bearing capacity. As well as describing the lower courses of corbelled brickwork, this chapter deals with masonry below DPC level — particularly its durability. Characteristic details Basic description In Georgian and Victorian times the foundations of small buildings tended to be very shallow in depth, often no more than halfa dozen or so courses ofbricks. 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 onrock, 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, with the maximum use of through stones (Figure 2.25). Old brick and stone footings Local authority byelaws in the last years of the nineteenth century required the course above the concrete to be twice the width ofthe wall to be carried, with successive courses above thatreducing by quarter brick width each side until the required thickness of wall was achieved. In modern construction, this stepped profile has been dispensed with as a simple mass concrete strip adequately distributes the load. Figure 2.24 Maximum use of brick headers in footings gives the best loadbearing qualities Main performance requirements and defects Strength and stability There is an important difference between the behaviour of brickwork builtin lime mortar, and brickwork built in cement mortar. Masonry footings which used lime mortars are much more tolerant of movement than are those built with cement mortars, the ductile nature of the lime mortar allowing the bricks to move slightly relative to each other when under stress. In consequence, footings of buildings built before the 1930s, before lime mortars began to be superseded by cement mortars, are much less likely to crack when the soils on which they are founded shrink or heave. Firm ground Figure 2.25 Typical stone footings widely used until the end of the nineteenth century BRE Garston Watford WD2 7JR BRE Building Elements Building services Performance, diagnosis, maintenance, repair and the avoidance of defects H Wharrison, ISO, Dip Arch, RIBA PM Trotman 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 Thebuilding 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 17 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 Preface vii building regulations, British Standards and Codes of practice, and the published recommendations of authoritative organisations. A defect— a shortfall in performance—is the product ofa fault, butwhile such a consequence cannot always be predicted with certainty, all faults have the potential for leading to defects. The word “failure” has occasionally been used to signify the more serious defects (and catastrophes!). The word fault as used here is not synonymous with electrical fault as defined in BS 7671, and defects and unsafe conditions take on a special significance in gas utilisation as controlled by the Gas Safety (Installation and Use) Regulations. A general requirement for “safety” arises because many ofthemeans adopted to satisfy the primary user requirements create potential or actual hazards. BRE has been greatly concerned with safety over the years. The most important aspects in the past history of building have been structural collapse and fire. Hazards to health probably come next, though they tend to be more insidious, and less easily recognised and defined. Other aspects include explosion (closely related to fire), and a variety of possible contributory causes of human accidents such as falls. Safety means the reduction ofthese hazards and risks ofaccidentto tolerable levels since absolute safety is virtually unattainable. A number of accidentrates are quoted in this book for various building services. As noted in the companion book Roof; and roofing, itis a matter for the collective Judgement of society, operating through building regulations and British Standards, whether these accidentrates are acceptable, for it could be very expensive to uprate all Standards to provide for better protection. Where the term “investigator” has been used, it covers a variety ofroles including amember of BRE's Advisory Service, a BRE researcher or a consultant working under contractto BRE. Particular terms used in connection with energy, central heating and air conditioning will be found listed in later chapters. So far as water terms are concerned, there has been a significant change in usage since the 1980s. Theterm “potable” water to describe water ofa quality suitable for drinking is nowno longer popular, though itis still contained in current Standards: the terms “drinking water” or “wholesome water” are preferred. “Grey water” is defined as waste water not containing faecal matter orurine, and “black water” is defined as waste water which contains faecal matter or urine. Acknowledgements Photographs which do not bear an attribution have been provided from our own collections orfromthe BRE Photographic Archive, a unique collection dating fromthe early 1920s. We are particularly grateful to Peter Mapp (Peter Mapp and Associates) who drafted Chapter 5.4, and to Geoff Dunstan (GDK Associates), who provided information and comments on parts of Chapter 2. To the following BRE colleagues, and former colleagues, who have suggested material for this book or commented on drafts, orboth, we offer ourthanks: EBartlett, AK R Bromley, A J Butler, DJ Butler, A Buxton, Sandy Cayless, R Cox, Maggie Davidson, P J Fardell, J Griggs, P Guy, the late Dr J Hall, MLyons, HP Morgan, Penny Morgan, B Musamnif, DrMD AA ES Perera, Prof G J Raw, Dr RRayment, REH Read, CScivyer, J Seller, M Shouler, N'Smithies, R K Stephen, DrP Warren, D Warriner, Dr Corinne Williams and B Young, all of the Building Research Establishment Ltd. Robert Rayment contributed much of Chapter 2.2, in addition to supplying information for other chapters, and Alan Buxton madea substantial contribution to Chapters 5.1 and 5.2. We have also drawn upon some notes prepared originally by Dr Rowland Mainstone when a revision to Principles ofmodern building was under consideration. HWH PMT July 2000 17 Chapter 1 This first chapter deals in simplified form with some of the basic underlying scientific and engineering principles which tend to affect the internal environment of the building as awhole. It also concentrates on those uses of energy which seem to be of most consequence to the occupants and which have a direct effect on their comfort, both thermal and visual. Asnoted inthe introductory chapter, the oldest buildings in the UK building stock have relatively little in the way of building services. In the days when these buildings were built, their occupants had to make do with the crudity of what was currently available. The application of scientific principles tothe design of buildings, although receiving some impetus with the technological developments of the Industrial Revolution, did not take off until the 1920s and did not really form a significant part of the education of architects until the middle years of the twentieth century. “The highest available knowledge ofpure science and the most effective methods ofresearch are needed in building as in any other field of research. Building research as a whole, however, is concerned with the principles ofan exceptionally wide range ofscience. Results ofpast scientific research are not at present Jully utilisedin building because there is no suitable bridge between the research worker and the architect or designer: * (The Department of Scientific and Industrial Research, 1919). Building physics (services) Although the principles underlying design for user satisfaction might not have changed significantly during the interwar years, the 1920s and 1930s, the application of scientific principles to the design and construction of buildings received a boost when the first volume of the book Principles of modern building was published in 1938 (see Chapter 1.1). Figure 1.1 Part of the plant room for a small office building. The rate of change of technological development is increasing, and plant rooms can become congested There is not the slightest doubt that since that time the increasing sophistication and consequent demands of users for improved standards in all kinds of buildings are driving an accelerating rate of change in the technological development of building services. In consequence, building services plant is getting more and more sophisticated (Figure 1.1), and services aretaking an ever- increasing share of the total costs of a building project. 18 1 Building physics (services) Chapter 1.1 At the time that the Building Research Station (BRS) was first established, relatively few houses had bathrooms and water closets, relying instead on outside “privies”. Central heating was rare, even in non-domestic buildings. Washday for many households began by lighting a gas or coal fire under the *copper”, stirring the clothes with a *dolly”, and “mangling” them by hand to a semi-dry state. Standards since then have risen out of all recognition. When the first edition of Principles ofmodern building“) was published in 1938, itwas possible to discuss in physical terms the functions and performances of the types of construction that were then being built, to indicate ways of predicting some of the performances, and to distinguish between good and bad Figure 1.2 Simple protection from the weather, which might have sufficed in years gone by, is no longer enough. When this substantial dwelling was built inthe nineteenth century, the many chimneys now surviving indicate that the main rooms were heated by open fires; even so, some rooms were unheated. Used since the early 1920s as offices, the servicing systems have needed to change out of all recognition The building as a whole practices. In therevised and expanded editions of 1959-61 this approach was further developed and extended to floors and roofs as well as to walls. But the focus on the building element —the wall, floor, or roof —remained. This concentration on building elements had the merit that it directly reflected the main interests ofthe designer at the detailed design stage. On the other hand it offered little general guidance on, for instance, the design of a complete spatial enclosure, the performance of which was of more interest to the user; and, for this reason, it could lead to overemphasis on some features and therelative neglect of others of equal or greater importance. There was a need to think more in terms ofthe whole system, at least when contemplating any major departure from already proven practice. Part 1 of the third edition of Principles ofmodern building was entitled “The building as a whole”. Thetext dealt with a number of important aspects of the performance ofthe whole building such as stability, ventilation, thermal and sound insulation, fire protection and daylighting, but there was little examination of the role of building services and the part they played in establishing comfortable conditions for the occupants. Since the 1960s, BRE has put much effort into examining the influence ofone services subsystem upon another; for example, the inter-relationship of different forms of heating systems with thermal capacity, thermal insulation and ventilation provision, and the effects of extraneous air leakage. The performance of the whole building ought to be viewed as a complex interaction of all its parts and all its subsystems, and what is in balance for one set of circumstances may not be the same for another. Although the carcass of the building can provide the occupants with some protection from extremes of climate, both winter and summer, it is the servicing subsystems which now provide the fine tuning and correction of any imbalances in comfort levels (Figure 1.2). The UK Climate Change Impacts Review Group have published estimates of the changes to the British climate that are expected toresult from global warming over the next 60 years. Climate change has particular relevance to buildings because they last a long time. Buildings now being Understanding dampness Effects, causes, diagnosis and remedies Peter Trotman, Chris Sanders and Harry Harrison ES constructing the future Contents A complete list of contents starts on page 212 Preface Readership Scope of the book Some important definitions Acknowledgements 1 Introduction What is dampness? Types of dampness Condensation Rain penetration Rising damp Construction moisture Leaking pipes Leaks at roofing features and abutments Spills Ground and surface water Contaminating salts Where is dampness apparent? Records of dampness related problems in buildings BRE Advisory Service records BRE Defects database records House Condition Surveys Changes lifestyle and construction Changes in domestic lifestyles Changes in external walling practice Changes in floor construction practice Changes in roof construction practice Changes in levels of risk BRE publications on dampness 2 Visible and hidden effects of dampness Health effects of mould and damp Mould problems and health Diagnosis Surveys Staining Visible moisture Condensation Rain penetration Rising damp Mould growth Surface moulds Algae, lichens and mosses Toxic mould Remedies Salts Diagnosis Remedies Frost Diagnosis Remedies Timber rot Types of fungi Occurrence of rot vii vii viii viii DONAR RIOWWWNNEA 15 15 18 18 18 18 18 19 19 20 20 21 21 21 23 23 23 23 23 25 25 25 25 Understanding dampness Remedies 26 Metal corrosion 28 Parts of the building at risk 28 Diagnosis 32 Remedies 34 Hidden dampness 36 Diagnosis 36 3 Measuring 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 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. vil Understanding dampness A 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 200MNs/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