Basement Waterproofing Design Guide.pdf

DESIGN GUIDEBasement waterproofing Foreword This publication is one of a series related to basements for housing. It has been produced under the direction of the Basement Development Group, which was initiated and is co-sponsored by the British Cement Association. Acknowledgments The British Cement Association (BCA) is grateful to the British Structural Waterproofmg Association (BSWA) for co- sponsoring this publication. It is also grateful for the assistance and comments provided by members of the Basement Development Group and for the considerable work of its Waterproofing Task Group in drafting and progressing this publication. Particular thanks go to Maria Hudlass and Steven Edwards of Servicised for the production of the figures. Thanks are also extended to all others who provided input to and comments on the preparatory drafts. Basement Development Group Waterproofing Task Group B Aspin (Chairman), House Builders Federation A K Tovey (Chairman), Tecnicom A K Tovey (Secretary), Tecnicom S Brown, Sika Limited F Atkins, National Housebuilding Council V Connolly, Renlon Limited D Burke, Zurich Municipal M Falla, Booth Engineering Services Limited M A Clarke, British Cement Association Z Ginai, Marley Waterproofing Limited P Hart, Institute of Building Control P Hewitt, Vandex UK Limited D James, Bovis Homes South West T Holloway, Renlon Limited A Jones, Stewart Milne Group Limited M Lenaghan, Servicised Limited B Keyworth, Architect I J Moffat, Fosroc Expandite Limited R S Reynolds, Institute of Clerks of Works J A M Padley-Smith, Mastic Asphalt Council and G R Sharpe, Association of Building Engineers Employers Federation Limited P Trotman, Building Research Establishment A J Parker, SCL Group Limited M Radford, RIW Limited Supporting Trade Groups Autoclaved Aerated Concrete Products Association British Sructural Waterproofing Association Concrete Block Association Mortar Producers Association Ready-mixed Concrete Bureau 48.058 Published by First published 1994 British Cement Association ISBN 0 7210 1475 5 Century House, Telford Avenue Price group D Crowthorne, Berks RG11 6YS © British Cement Association 1994 Telephone (0344) 762676 Fax (0344) 761214 From April 1995 the code will be (01344) All advice or information from the British Cement Association is intended for those who will evaluate the significance and limitations of its contents and take responsibility for its use and application. No liability (including that for negligence) for any loss resulting form such advice or information is accepted. Readers should not that all BCA publications are subject to revision from time to time and should therefore ensure that they are in possession of the latest version. toppings and coatings Ancillary materials 7 Waterstops Bandage joint systems Membrane protection products Other design considerations 7 Thermal insulation Condensation Vapour control Chemical barrier System restraint Substrate movement Expansion joints Defects and repair Site investigations 8 Groundwater Soil type and conditions Movement risks likely to affect basements Construction options 10 Basement site locations and forms Design factors affecting construction Waterproofing details 13 Details of waterproofing options and forms of construction Selection procedure 17 Guide to assessing basement designs Assessing risk Glossary 18 References 19 Other publications relating to basement structures Production: Words & Pages 1 . Contents Introduction 2 Scope Design principles 2 Basement usage 2 Site information 2 Deciding on form of construction 3 Forms of construction Factors affecting choice of construction Characteristics of construction forms Suitability of construction forms Form and characteristics of waterproofing systems 5 Category 1: Bonded sheet membranes Category 2: Cavity drain membranes Category 3: Bentonite clay active membranes Category 4: Liquid-applied membranes Category 5: Mastic asphalt membranes Category 6: Cementitious crystallization active Systems Category 7: Proprietary cementitious multi-coat renders. as defined in BS 8102. the manufacturers of the systems under consideration are contacted immedi- Yes ately for early advice and help on the waterproofing design. penetration through external waterproofing and then ronment would be acceptable. be regarded as difficult and possibly uneconomic to build on. the risk of water permanent workshops or garages. and defines them in Grades for how long the water table stays high are also impor- 1 to 4. which is Grade 3. Is construction ised task. it is important to identify it. Basement usage A watercourse or water table that rises and falls with Table 1 of BS 8102 relates environmental performance climatic changes must also be identified. It is unlikely that a Grade 4 environment would be Including a basement maximises available land space. tant. construction Type A/B/C tion may occur. Geology Water table Site survey Scope Topography Soil drainage The details and comments given in this publication are limited to Grade 2 and 3 internal environments. High water tables present the greatest risk of failure of the water-tightness of a basement. The Grade 3 environment is for ventilated residential and working areas which require a drier environment. in particular. 2 . and comments on other associated construction matters. and a Grade 2 envi. required in a domestic situation. benefit by being offered houses with greater potential(1).and then immediately falls again. How often and levels to basement usage. Choosing a suitable basement construction may be F i g u r e 1 : Principle selection criteria divided into four main steps: Decide on basement usage Gather site information Site information Decide on form of construction The gathering of site information is dealt with in Site Decide on form of waterproofing investigations on page 8. is thermally efficient sary. after heavy rain tion. Grade 3 environment than to upgrade it later. Proposed Basement use A companion publication. it is better to construct a basement to a high for a much longer period. However. and other areas where the performance level permits no water penetration. If it did become neces- provides more stable construction. Basement waterproofing: Site development Environmental guide(2) provides advice on the application or installation requirements of the various waterproofing systems. Some basements may be for . in the flow chart in Figure 1. A basement performing to Grade introduced onto most sites and. once the design team No buildable? has given the system some thought. However. but higher levels of Basement water vapour would be tolerable and surface condensa. The British Structural Waterproofing Association Solution can provide details of manufacturers of the different generic waterproofing systems and of appropriate specialist waterproofing contractors. It is recommended that. If the water table rises briefly . Most basements will be for domestic accommoda. a few points need to be considered when selecting the form of construction These and other factors needing consideration are shown and waterproofing system.say. Basements can be economically internal waterproofing. Certain Introduction forms of construction and waterproofing may lend Basements provide an opponunity for the builder to themselves to upgrading more readily than others (see achieve a good return on his outlay. have clear 2 can be upgraded to Grade 3 or 4 by incorporating advantages on sites with poor ground that may otherwise additional ventilation and/or dehumidification. and his customer to Construction options on page 10). If there is a perma- nently high water table. which are appropriate for residential Design House type and basements. This publication is intended to help the builder or designer arrive at the most appropriate form of construc- tion and waterproofing solution. a Grade 1 environment may be upgraded to and offers ideal quiet areas and further space for storage Grade 2 by introducing a drained cavity system or or accommodation. Selection of waterproofing system Design principles The specification of waterproofing systems is a special. since usage through the structure is less than if the water table stays may change. shape considerations Foundations The Grade 2 environment is for use as workshops and design plant rooms. tanked protection External or internal Crystallisation. Type A. from either itself or in combina- construction tion with the superstructure. together with the and/or the groundwater must be established to ensure factors affecting their choice.drained protection Figure 2: The three forms of basement construction 3 . In addition. hydrophilic. and discussed overleaf.structurally integral protection Floor drainage options Preformed cavity floor and wall drain system Engineering brick with open joints at intervals Floor finishes Cavity drainage system Drained and Drainage Tiles Membrane No fines former concrete Drainage sump ventilated cavity with pumped outlet Type C structures . purposes. The main contractor may need to lower the water table temporarily to enable the construction and waterproofing to go ahead.The likely presence of water and the position of the the most suitable combination of structure category and water table must also be established for construction waterproofing system is selected. B and C. External Sandwiched Intenal waterproofing waterproofing waterproofing Type A structures . are greater than the forces Forms of construction that would be generated by the water pressures as the BS 8102 describes three forms of basement construction: water table returns to its original level. waterstop as required or injected waterstop A non-integral kicker Water-resistant will require one waterstop where it adjoins the slab Water-resistant reinforced reinforced concrete and another at its intersection with the wall concrete wall and slab wall and slab Type B structures . any lowering of Deciding on form of the water table will need to maintained until the loads acting on the basement. These are shown diagrammatically in The existence of any aggressive elements in the ground Figure 2. which depends upon through lack of compaction. If the water table is high only briefly. Most designs patio. The chosen structural waterproofing pass through it. they can be generally classified thermal contraction and shrinkage. where the levels may vary the two extremes described above. by definition. this form reduce the risk (see Assessing risk on page 18). Type A ing system incorporated externally during construction. the greater the risk of significant dampness or even partial flooding. movement. many factors and no two sites can. Invariably built of reinforced or prestressed concrete. The watertightness of the Type A basement relies totally Or it may be applied internally to the finished basement. any defects permanent reliance on this cavity to collect groundwater in the system will allow moisture to move under capillary seepage through the structure and direct it to drains or a action. Of these. Externally applied Type B (structurally integral protection) structures systems will require subsequent excavation. water vapour movement. The effects of water table conditions on the three service loading. in Type A structures. These include natural groundwater as an integral shell. many factors need to be reliant upon the design and construction of the basement known (Figure 1). also provide high resistance to Since total reliance is placed on the waterproofing system water vapour movement. therefore. the ingress might not be enough to show itself. However. The external basement wall must will increase the risk of interstitial condensation and provide enough resistance to water ingress to ensure the cavity accepts only a controlled amount of water or hence possible damage. Locating the requires the structure itself to be constructed as an source of a defect in a system not continuously bonded integral water-resistant shell. or free-drained site. Defects can then be more readily of BS 8007 or BS 8110. additional waterproofing systems may be applied either internally or externally to of the basement floor. Type C (drained protection) structures incorporate a drained cavity within the basement structure. reinforced or plain concrete or masonry with the structural waterproof. This Form of construction can. with an integral construction or external system to Without the addition of a separate membrane. basement structure must be designed within certain strict for example. nants. groundwater contami. the water table is consistently below the level designed to be water-resistant. be said to contamination of construction joints. logged conditions. on the effectiveness of the waterproofing system. account must be taken of the need to gain access if a defect occurs. honeycombed concrete. using a concrete of low permeability. the basement will fill to the level of the water table. this will usually result sump for removal by drainage or pumping. consideration must system must be able to withstand hydrostatic pressure always be given to what would happen as a result of any from groundwater. Type B structures need to be carefully constructed to of the basement floor. in some dampness in the structure. but will not necessar- ily show itself on the internal surface. affected by the attachment of skirtings etc. groundwater level is consistently above the level careful construction. levels or perched water tables. also provide high resistance to longer it stays high. However. depending on the water. These can all be as follows: reduced by correct specification and design and by • Athe high or perched water table where. finally entering the basement as free waterproofing system. then an internally applied membrane may be would be carried out according to the recommendations easier to maintain. or to provide further protection. dampness. any defects will allow water to pen- pointing to produce a surface good enough to accept a etrate the structure. cracking due to be the same. The proofing system used. which give guidance on the grade found and repaired. Type A (tanked protection) structures have no integral Characteristics of construction forms protection against water penetration and therefore rely Any structural waterproofing membrane designed to totally and permanently on a waterproofing membrane to resist a hydrostatic head should not let any free water keep water out. the faces of the walls and floors to control water vapour • Abetween variable water table. Although they are • where A permanently low water table. in practice. The structural wall may be prestressed. natural drainage and soil type. by far the The most common defects are permeable concrete most significant is water table level. to the substrate wall can add further complications. This form of construction can. Factors affecting choice of construction Type B To consider the performance and likely reliability of The watertightness of the Type B construction is totally these three types of structure. 4 . basement types are discussed below. However. The of construction may not be as resistant to water vapour performance of internal waterproofing systems can be movement as a Type A or C. together with any superimposed or defect. Where the defect is small. the cavity system may not With a varying water table. With a Masonry walls may require a cement rendering or flush high water table. and appropriate joint details. the Where access is. If this water is not removed. An internal system could be used of concrete and steel spacing. depending on the water- proofing system used. or is liable to be. If this is not so. There is Where the site is permanently free-drained. where appropriate. avoid defects that let water through. significant water ingress cope with the deluge of water from a high water table or through defects will occur only during storm or water- during storm/flood conditions. reinforced or plain decoration or surface coating that acts as a vapour check concrete or masonry. or by fittings applied subsequently. water. any Structural walls may be prestressed. severely restricted by. a permanent external in-situ pavement or parameters to ensure it is water-resistant. This is because these structures can themselves be designed to be • by a loading coat When applied internally. controlling water ingress at construction joints is to use a Where the site drains well enough to prevent the crystallization or hydrophilic system that reacts in the build-up of hydrostatic water pressure.using one system with another . horizontal. a Type B construction with the areas most commonly associated with leaks. It is imperative that all continuous and stopping these is usually fairly straightforward. An alternative method of failure. and on the initial resistance Category 4: Liquid-applied membranes of the structure to water ingress.Construction joints need particular attention as these are With a very high water table. great care is required in the placing and Type C) could be considered to carry the smallest risk of compaction of the concrete. all three forms of presence of water to seal the joint. or internally with a loading coat strong enough to resist hydrostatic pressure. Most proprietary systems and materials are covered by In a free-draining site. so avoiding the need for external excavation. Do Variable water tables present less of a problem. attached to the enabling works (reverse tanking). Additional waterproofing protection may be used. They are should blockages occur. Type A structures are not recommended in areas with an undrainable high water table. it is rare for a defect to be so British Standards. Modern types of formwork and kickerless construction techniques mean waterproofing systems that kickers no longer need be part of the construction process (see Figure 2 on page 3). becomes blocked. but On a free-drained or sloping site. Remedial action can usually be carried out from the and executed. Since reliance has often to be placed on the waterproof- ing system. dimples form permanent cavities between the structure 5 . they need to be restrained resistant to the ingress of water under a hydrostatic head. warranties. the cavities may be led subsequently fully bonded by means of a specifically to a soakaway to handle any ingress from. and conditions. the designer must ensure the materials are With a high water table. construction carry little risk of damp penetration. inside. • They are of consistent thickness and quality A well-built Type B construction carries a low risk of • groundwater May provide protection against aggressive soils and when applied externally serious failure in a high water table.must be avoided because of the danger of incompatibility. A Type C construction could provide a suitable form of Category 2: Cavity drain membranes structure. sloping or vertical waterproofing be specified. They are drainage capacity and result in dampness or flooding. Category 5: Mastic asphalt membranes Category 6: Cementitious crystallization active systems With a permanently high or variable water table. Failure of drains or mechanical pumps could result in Category 1: Bonded sheet membranes • Blockage of the cavity by silt or other contaminants could result in flooding. can arise in several ways: toppings and coatings • flooding. where any water can be easily drained to a Cavity drain membranes are high-density dimpled convenient point. dampness on the internal surface becomes a possibility. Hybrid systems . to the pouted ing surface water. The back is completely retaining but the front is not. say. Design considerations Suitability of construction forms • shrinkage Flexible and able to adapt to minor movement and within the substrate Generally. (The design of the structure Bonded sheet membranes are generally cold-applied or heat-bonded to the finished structural walls. Both are should allow for clearing of silt and rodding of drains modified bitumen on a range of carrier films. in one proprietary waterproofing system. minor defects in the concrete properly selected and adequate for the proposed location usually result in only small amounts of water penetrating. defects Category 7: Proprietary cementitious multi-coat renders. suitable only for uncomplicated foundation systems such as plain rafts Type B structures are less likely to result in water ingress owing to the integral protection of the structure. While a preformed plastic drained cavity former applied attention needs to be paid to jointing and positioning internally (effectively turning the construction into water stops. formulated pressure-sensitive adhesive. placed against the structure. The amount of free water Category 2: Cavity drain membranes entering will depend on the volume of external water Category 3: Bentonite clay active membranes and its hydrostatic pressure. Type C There are several categories of structural waterproofing: The Type C construction relies totally on water collected Category 1: Bonded sheet membranes in the cavity being taken away. for example on sloping sites where the polyethylene sheets. unless not mix hot and cold systems. percolat. the water table stays high for a long time. Care in the placement of concrete and waterstops • toSubstrate occur must be free from surface water for bonding (Figure 2) at construction joints is essential. Agrèment certificates or manufacturers’ serious that water comes through by capillary action. Composite An increase in the ingress of water could exceed the polymeric sheet membranes are also available. If the soakaway silts up or the drain concrete.) applied externally. but defects in • Generally. The construction of a ‘kicker’ either during or after pouring the floor slab should not be encouraged as it is Form and characteristics of difficult to construct without defects. but retain a degree of flexibility. • Can protect the structure against aggressive soils and Design considerations groundwater when applied externally • Can be applied internally with no loading coat • Have high substrate adhesion and chemical resistance requirement • Must be applied to a dry surface • Effective against severe groundwater infiltration • When applied internally. piles and ground beams • before Requires protective screed on horizontal membrane loading coat is installed • With high or variable water tables. there is little risk of entering the cavity is collected and drained or in one coat being carried right through the pumped away total membrane • They are of consistent thickness and quality • May provide protection against aggressive soils and • Flexible and able to adapt to minor settlement and shrinkage within the substrate groundwater when applied externally • Simple internal applications can overcome • Substrate must be dry before application complicated designs. They can be applied both externally and inter- nally. blockages or failure of drains/pumps may lead to flooding • unsuitable for Externally applied membranes are generally complicated foundations such as piles Category 3: Bentonite clay active Category 6: Cementitious crystallization membranes active systems Bentonite clay active membranes are sheets of sodium Cementitious crystallization active systems are coatings bentonite clay sandwiched between two layers of applied as internal or external slurries. it free lime in concrete. renders or mortars. They cool to a hard. the loading coat must be strong multi-coat renders. When the clay meets water. generally in two coats as a bitumen solution. coating are applied as a layer(s) to form a dense. They are used internally to drain Category 5: Mastic asphalt membranes and control water ingress. Mastic asphalt membranes are applied in three coats as a hot.g. elastomeric urethane or modified Category 7: Proprietary cementitious epoxy. e. such as Liquid-applied membranes are one. defects are easy to find and repair • Require good surface preparation • Provide a durable surface suitable for direct finish • thickness Careful application needed to achieve correct of dried film • aggressive soils externally. thus accommodating minor movement and shrinkage within the structure external. • Minimum preparation of substrate needed Design considerations • There is no hydrostatic pressure on the system: water • defects Because of the multiple coats. If internal.or two-part systems. All • Easily applied to difficult substrate profiles are designed to be used inside the structure but can be • Elastic and flexible. they maintain continuity of membrane coatings are premixed slurries applied as a thin layer. must be restrained by a • Easily applied to difficult substrate profiles loading coat if subjected to a hydrostatic water pressure. Design considerations Design considerations • construction Provide in-depth waterproofing of concrete and joints • Minor defects in placing should self-seal • The chemicals remain active and will self-seal leaks • They are simple to apply • In construction joints. waterproof Design considerations coating. unless used as a Proprietary cementitious multi-coat renders. as in Type A construction • When applied internally. gaps or voids in the membrane. they assist repair of local defects • The substrate does not need to be dry before • Applied externally. Application can • Installed after the construction of the basement be external or internal. By reacting with biodegradable cardboard. may protect against aggressive application soils and groundwater • Minimum preparation of substrate is required • Will not self-seal cracks greater than hairline (0. the loading coat must • Defects may he rectified before completion be strong enough to resist hydrostatic pressure. In the latter case. toppings and coatings enough to resist hydrostatic pressure. they block can swell to many times its original volume. sealing any cracks and capillaries. waterproof membrane. honeycombing They are applied cold. Waterproof renders or toppings Design considerations consist of a layer or layers of dense cementitious material incorporating a waterproofing component.3 mm) • Must not be used in acidic or excessively alkaline soils • Cannot be used on building materials containing no free lime Category 4: Liquid-applied membranes • Will not waterproof defective concrete. Cementitious • Being jointless. toppings and vapour barrier in Type B construction. When appplied can protect against and groundwater 6 . and the internal shell. This category of membrane is used externally. mastic liquid. fillers and chemicals to be further insulation to comply with the Building Regula- mixed on site as a slurry. construction and contraction joints. 7 . The strips may be wholly of hydrophilic Other design considerations material. Any external insulation must have the concrete. • inStrips or profiles of hydrophilic materials which swell water.dictate the form of construction and the presence of water. They should therefore be External waterstop profiles are also available and are chosen in consultation with the supplier of the water- positioned on one face of the concrete. Plain web profiles are available for non-moving or low. loss of its thermal insulation properties. These products are not suitable for use in low water absorption and be frost resistant to prevent expansion joints. This can is movement. or protruding from underneath it. Alternatively. if vertical protection and drainage are required. certain aspects are common concrete since they avoid the problems of breaking out to several systems. The form of structure and on other design and construction use of water-swellable strips is limited to low-movement aspects such as the need to control water vapour. Membrane protection products movement construction and contraction joints. They can be applied against existing waterproofing already given. Alternatively. according to the location and sealed. bonded across the joint Rubber or flexible PVC waterstops with a suitable adhesive. They also eliminate a 'wet trade' operation resist the passage of water through a joint from either and allow the following works to continue immediately face. or surface waterstops simplify the shuttering and installa- tion but will resist the passage of water only from the A protection board may be used in vertical applications. protection boards Alternatively. either alone or as pan of a composite with a rubber or PVC extrusion Bandage joint systems Where large or unusual movement is expected in joints • Cementitious crystallization products or cracks . These consist of strips of synthetic polymer membrane. when the exit of the tube is the following types. where insulation is required. the manufac- These are extruded profiles fabricated with junction turer’s advice on application method and adhesive pieces to provide a linked continuous system through all should always be followed. material or filler. in basement walls . Profiles If construction operations may damage applied mem- incorporating a centre bulk or box are used where there branes. adequate protection must be provided. a geocomposite drainage sheet could be used: Water-swellable waterstops its greater cost may be offset by the reduction or elimina- Such waterstops depend upon a sealing pressure being tion of hydrostatic pressure on the membrane as a result developed by the water absorption of a hydrophilic of the better drainage. it flows freely out of the perforations into any function: cracks. These are known as internal or They are more convenient since they provide immediate centrally placed waterstops. The tube is then cast into the construction joint. they are best avoided. As systems vary. as they are more difficult to install and after laying. face in which they are installed. fissures or holes in the construction joint. within the pores and capillaries of waterproofing system. Protection boards should be rot-proof and robust enough to withstand site operations. Internal waterstops will protection. However.bandage • Post injected systems joint systems may be used. of the structure since the lower basement slab is more efficient than a slab at ground level. The • Rubber or flexible PVC extruded profiles injected material then sets to seal all water paths through the joint. it may - of the first-poured concrete before the second pour. They are available as strips for bonding or nailing to the first-placed concrete immediately before the second pour. they may reflect any cracking of the Post injected waterstops These consist of a perforated or permeable tube fixed to • cause Fittings fixed mechanically through the system can problems and should be avoided the first pour of concrete in the construction joint with either end attached to fittings connected to the formwork.• substrate Being rigid. Ancillary materials After the concrete has hardened a polyurethane resin or Waterstops other propriety fluid is injected under low pressure to Waterstops for basement construction may be of one of flow through the tube and. The depending on whether it is placed inside or outside the waterstopping action results from salt crystallization. The surrounding Cementitious crystallization waterstops earth will also improve the thermal transmittance of the These differ from the previous two categories in that the basement walls and there may be no need to provide product consists of cements. These rear-fixed proofing system. can cause problems when the concrete is being placed and compacted. waterstops may be cast totally within the supplied by most membrane manufacturers may be used. or compounded with a rubber.in both new and remedial work . consist of vertical blockwork and a 50 mm screed to horizontal surfaces. The final selection will depend on the to install a conventional rubber or PVC waterstop. as in expansion joints. Hydrophilic material may be applied to a conventional Thermal insulation PVC waterstop profile to provide a combined system that Including a basement can improve the thermal insulation may also cater for expansion joints. site-placed concrete. the joints or discontinuities within a concrete structure. or part of a As well as the general characteristics of the categories of composite profile. The slurry is applied to the face tions However. and there can be problems in locating defects in applied externally can cause interstitial condensation (3). Categories 6 and 7 are more brittle with into the air. The site history and name clues such as “Pond with aggressive chemicals. therefore. therefore. the condensation risk can be systems can be affected. When applied controlled. externally. by the attachment of The advantages/disadvantages of vapour permeable/ skirtings etc. 4 and 5 are employed internally. In most domestic situations. in which case a to be assessed and reference should be made to BS 5930 category 6 or 7 system will be needed. the condensation risk increases and more care is needed in the choice of waterproofing and Site investigations insulation systems. some structures need to influenced by the ground conditions. used internally without a loading coat. If the water table is high. the performance of internal waterproofing and permanent ventilation. it is far better to design the structure in a way A vapour-permeable waterproofing system can thus be that avoids expansion joints. although joints can be detailed to cater for movement. 8 . if the water table is low. Condensation determined and the membrane manufacturer must be Because window areas are often reduced. They will crack if the substrate cracks but may always pass from the ground into a basement. careful consideration must be given to the watering would be required. to decide whether water vapour needs to be controlled or not . 3. be less natural ventilation in basements than in other areas of a house. seasonal position below ground will need to be estab- However. as indicated in Characteristics of reduced to be no worse than in the rest of the dwelling. impermeable systems are then usually negligible. With externally geous if the vapour tends to move from the ground into applied systems. there tends to consulted. construction forms on page 4. It is often the basement but similarly will allow the relative humid- difficult. “Investigation of the site is an Vapour control essential preliminary to the construction of all civil engineering and building works”. Groundwater Water table Chemical barrier The existence of a watercourse or water table and its An external membrane can protect the main structure. methane and other gases. 6 and 7 can be risk and effects. Access following construc- effect that the waterproofing system has on the resistance tion may not be desirable or possible. permanently or for long periods. this may mean excavation. They are therefore generally more System restraint prone to condensation. so heating and air circulation Categories 1. Although this is performance of the finished structure will be greatly often seen as an advantage. 4 and 5 need to be restrained so that need to be carefully designed to ensure condensation is they can resist the forces involved. Defects in the materials or in their A system that acts as a vapour check can be advanta- jointing may require remedial treatment. When categories 1. This will take up in detail here. Lane” can help. systems that are not continuously bonded.see Condensation above. from within the structure Expansion joints towards the ground. In practice. but will allow relative humidity within the basement to rise if the reverse conditions Defects and repair apply. 3. the structure provides the restraint. Particular This should not be a problem as long as it is allowed for difficulties will arise where the water table is high in the design. which in turn depends on the temperature usually accommodate some flexing or design cracking of and the amount of free water available to be released the structure. a basement are controlled by properly designed heating However. they need Condensation in basements is too complex to be covered to be restrained by a loading coat. so. even years later. However. The vapour for detailed information on site investigations. This is particularly As well as controlling water ingress. water vapour will move. to reach defects in externally applied ity to rise if the reverse is true. Reference 3 explains how to estimate its space within the structure. where internal conditions in internal waterproofing system may be preferable. 5 and 7 rely on their impermeability to control water ingress. advantageous if the vapour tends to move from the inside to the ground. 4. Categories 2. If the environment is controlled solely by natural air movement. Evidence of a flooding site could suggest their precise nature and concentration must be an impermeable soil or a high or perched water table. The vapour pressure in Substrate movement a specific area relates directly to the humidity of the air at Categories 1 to 5 have reasonable strain capacity and will that point. if the ground or groundwater is contaminated lished. low strain capacity and so are less tolerant of structural Although it is commonly thought that water vapour will flexing. Several factors need allow for water vapour movement. this is not still control moisture ingress if the cracks are fine. categories 1 to 5 can important for basements. in which case an to water vapour. water Care is needed when considering systems used with vapour will penetrate the basement but usually at such a expansion joints: always consult the manufacturer. Categories 3 and 6 are active systems and can ‘self-heal’. low rate as to be of little consequence. or by the application of subsequent fittings. Categories 1. since ground de- In general. a vapour check systems. since the materials used and the also act as an effective vapour check. Brief resistance of category 7 systems can vary significantly details of some of these aspects are given below. with the product.. However. As stated in BS 5930 (4). Water vapour tends to move from areas of high vapour pressure to low vapour pressure. It is important. rock flour. Other materials Soft: chalk. little or no fines Well graded gravel-sand Practically impervious Very slight mixtures with excellent clay binder Gravels and Uniform gravel with Excellent Almost none gravelly soils little or no fines Poorly graded gravel and Excellent Almost none gravel-sand mixtures. etc. impervious medium poorly graded sand-clay mixtures Silts (inorganic) and Fair to poor Slight to medium very fine sands. Excellent Almost none little or no fines Sands with fines. silty Fair to practically Almost none to gravel. Fair to practically Almost none to rubble impervious slight Well graded gravel and Excellent Almost none gravel-sand mixtures. clayey sands. silty or clayey fine sands with slight plasticity Soils having low Clayey silts (inorganic) Practically impervious Medium compressibility Organic silts of low Poor Medium to high plasticity Silt and sandy clays Fair to poor Medium to high (inorganic) of medium plasticity Soils having medium Clays (inorganic) of Fair to practically High Fine soils compressibility medium plasticity impervious Organic clays of medium Fair to practically High plasticity impervious Micaceous or Poor High diatomaceous fine sandy and silty soils. soft rocks. fat clays Organic clays of high Practically impervious High plasticity Fibrous organic soils with very high Peat and other highly Fair to poor Very high compresibility organic swamp soils 9 . little or no fines Coarse soils and other materials Grave1 with fines. clayey gravel. elastic silts Soils having high Practically impervious High Clays (inorganic) of compressibility high plasticity. impervious slight poorly graded gravel-sand-clay mixtures Well graded sands and Excellent Almost none gravelly sands. little or no fines Well graded sand with Practically impervious Very slight excellent clay binder Sands and sandy Uniform sands with Excellent Almost none soils little or no fines Poorly graded sands. silty Fair to practically Almost none to sands. Excellent Almost none hardcore.Table 1: Characteristics of soils which effect basement construction Material Major divisions Sub-groups Drainage Shrinkage characteristics or swelling properties Boulder and Boulder gravels Good Almost none cobbles Hard: hard broken rock. For example. The likeli- hood of radon can be established from the underlying Type A or C construction may be used if the site is free- geological structure. Excavated material may be re-used to landscape around basements partially The presence of. It is important. and includes guidance on ground contaminants. Some slags and other residues often contain toxic materials and some furnace ashes may be reactive. or potential for. its drainage characteristics. properties would be at little risk impermeable. with cut- water reaching the basement wall. in particular. their positions on. Such sites can also present risks from acid wastes. for three types of site: sloping. Sloping sites Soil type and conditions Sloping or elevated sites allow both full and semi- The type of soil can greatly influence the quantity of basements or split-level dwellings to be built. provisions. The remains of former buildings or structures on the site need to be assessed. flat and infill. Perimeter drain to discharge to downside If the risk of movement is high. for example. adapted from reference 5.can result in ground movement and affect the loadbearing capacity of soil. Economical Type A soil type and.caused. Check the Flat sites ground for materials that are detrimental. soil conditions. tanked basements or Type C structures can therefore be Table 1. mineral oil shales. Perimeter drain to Clay and peaty soils are particularly prone to volumetric discharge to downside (a) Semi-basement changes leading to varying foundation pressures and movement. They are best removed to avoid differential movement due to bearing over strong points. Cut-off drain Movement risks likely to affect basements A change in ground moisture content . movement joints should be considered. simply designed in concrete or masonry. Steeply sloping sites may have high land-slip risks. Some soils contain chemicals that may harm both the structure and the waterproofing system. by the removal of trees . to determine the from percolating groundwater. which tend to be be effectively drained. and guidance for its control may be draining or is in an elevated position with drainage found in reference 6. such as peat Flat sites provide the opportunity for basements wholly and sulfates. radon and methane should be ascertained. giving the dwelling an elevated aspect. although expansion joints are a common solution. the prevailing terrain. for example. gives the characteris- built. which should be assessed before proceeding further. and other fill materials. Ground drainage Construction options The topography of the land and the direction and movement of any groundwater should be determined as Basement site locations and forms they will have a bearing on any proposals to provide There are many potential basement locations. Where possible. natural gases such as below ground. they do present problems. or partially below ground (Figure 4). Design drainage to reduce local groundwater pressures. Figure 3: Basements on sloping or elevated sites 10 . particularly in a waterlogged site. they may not be appropriate because of the difficulties of maintaining watertightness. Although such matters can be catered for structur- ally. Any new construction proposals requirement of the end user. water tables. Methane and other gases are likely to be linked to infill and made-up ground. particularly where large amounts of organic matter have been buried. Since these sites can normally present fewer problems than clays. but instead should design discrete boxes that can be sepa- rately waterproofed. Particular care is needed where there are changes in the Cut-off drain soil strata that may cause differential foundation move- ment. drainage provisions. therefore. forms and waterproofing methods will therefore depend If there are any drains or land drains. Typical locations and forms should not interrupt drains that still function unless of basement construction are illustrated and summarized measures are taken to redirect them or to intercept the water by a new drainage system. with tics of the main soil types. Free-draining soils and-fill options (Figure 3). Reference 7 gives information on site preparation and resistance to moisture. proximity of adjacent buildings and the should be established. designers should not (b) Split-level dwelling attempt to create waterproofed expansion joints. However. this form of construction can be adopted Perimeter drain to for both flat and sloping sites. If so. Infill sites between adjacent dwellings can be developed (Figure 5). Design preference is for Type B construc- tion. discharge to downside (d) Projecting basement Figure 3: Continued (a) lndependant structure with basement wholly below ground (a) Basement partially below ground Drainage sump Retaining bund wall (b) Semi-basement on inflll terrace development (b) Basement wholly below ground Figure 4: Basements on flat sites 11 . it can be difficult to achieve continuity in external or pre- applied waterproofing systems. fluctuating or perma- nently high water tables. Alternative systems should therefore be looked at. Where adjacent properties have to be underpinned. Clearly. As there may be problems with perched. Semi-basements on infill sites can probably use a bunded catchment area. these may be more (c) Split-level with basement wholly below ground and with susceptible to periodic flooding from existing defective side access water mains. substructures designed in water-resistant Type B construction would therefore be advisable. Cut-off drain Infill sites Inner city areas provide more opportunities for house basement construction because high kind values increase property costs. Basements constructed on a flat site in low-lying areas with impermeable soils can be difficult to drain. Any window fire exit must be above the highest anticipated water level. with a drainage sump (Figure 5(b)) for rain- water. perhaps with internal waterproofing or drained cavity provision. the bund walls should be designed as Type A tanked construction or Type B water-resistant Cut-off drain concrete. (c) Staggered foundations An additional water-activated pump may be used to deal with run-off water. which are normally installed outside the structure. can be used to ensure that Foundation design the severity of water conditions does not exceed that Structures should be designed to keep foundations as simple as possible. They can be used either to extend the application of Type A and B construction or to provide shapes are best avoided. Such pumps. the designer should The orientation of the basement area to the general flow consider 'buildability' and the acceptable level of risk. Design factors affecting construction Basement drainage Attention should be given to the drainage requirements for Type A tanked structures and reinforced concrete Type B structures. sub-drainage suggested waterproofing options. When deciding on the form of feed back to the pump inlet. Type A structure Confine to sloping or elevated sites with good drainage External or internal waterproofing High-risk design due to lack of continuity between wall and floor. but may not be appropri. so improving the total water.see Figure 6. Any L. risk of hydrostatic pressure.or U-shapes with a re-entrant angle against the Consideration must also be given to how remedial work natural drainage flow can act as dams and increase the may be carried out if this performance is not attained. relative to cost of achieving the desired performance. construction and waterproofing. to achieve continuity of waterproofing. The outlet from such Complicated foundation designs do not lend themselves pumps must discharge to areas where the water cannot to external waterproofing. as with a clay soil. Expansion joints and complicated taken for design. Where basements are Common foundation designs are shown in Figure 7 with constructed against the flow of water. Therefore the Installing a geocomposite drainage sheet and fin or land preference is for sandwich drains will help deflect and drain water away from the construction with provision perimeter of buildings. of groundwater should also be considered . ate for all water-proofing systems. should be provided and graded to storm drains or open outlets on the downside of the building. This can be particularly useful where the water table becomes perched because the soil is too Figure 6: Continued impermeable to handle the percolating surface water. since they are points of weak- an additional escape for water. ness and need a lot of attention to detail. for external relief drainage proofing (see Waterproofing details on page 13). Lack of proper drainage to basement surrounds may result in hydrostatic pressure and subse- quent leakage through defects in the waterproofing or Stepped and staggered foundations make it difficult concrete. Reinforcement Drainage may be require may be required to control to alleviate build up of cracking hydrostatic head (a) Strip foundation (a) Non-preferred orientation Type A structure Confine to sloping or elevated sites with good drainage Orientation of basement External waterproofing may design to avoid possible be required to modify the 'damming' of the ground exposure situation of the water flow retaining wall Difficult to achieve continuity of waterproofing membrane when applied externally (b) Preferred orientation (b) Piled ring beam and reinforced masonry wall Figure 6: Drainage and orientation Figure 7: Typical foundation designs 12 . when applied externally Two leaves of structural wall (not tied) (c) Piled foundation Membrane Type A structure Confine to sloping or elevated sited with good drainage Simple design External waterproofing may be required to (a) Sandwiched waterproofing modify the exposure situation of the retaining wall (d) Reinforced masonry wall with reinforced concrete raft Membrane/waterproof render Type B structure Suitable for permanent Concrete or masonry or variable water tables structural wall above slab level (not waterproof) Reinforced concrete Protection/loading coat design to BS 8110 or (if required) BS 8007 as appropriate May be combined with external/internal waterproofing or drained cavity construction to (b) lnternal waterproofing enhance performance (e) Reinforced water-resistant concrete box Type C structure Suitable for permanent or variable water tables Protection (as specified) above slab level Reinforced concrete Membrane design to BS 8110 or BS 8007 as appropriate Concrete or masonry Internal drained cavity structural wall construction (not waterproof) (f) Drained cavity construction with piled foundation (c) External waterproofing Figure 7: Continued Figure 8: Alternative waterproofing systems 13 . The principal details and Difficult to achieve continuity elements of the main waterproofing systems are shown of waterproofing membrane in Figure 8. Waterproofing details Type C structure Details of waterproofing options and forms Ideal for sloping or elevated sites of construction External waterproofing may The principal form of construction outlined in Deciding be required to modify the on form of construction on page 3 may involve a variety exposure situation of the retaining wall of waterproofing options. each waterproofing system may be used as the sole protection or combined to give addi- Preformed cavity tional protection. all laps in the waterproofing system must Basement be fully weathered and sealed. structure not providing Type B standard Figure 8: Continued Water-resisting structural wall to BS 8110 or BS 8007 as appropriate As already indicated. no waterproofing to walls. Permanent masonry Structural wall enabling works Ventilated cavity Concrete or masonry structural wall (not waterproof) Concrete or masonry structural wall (not waterproof) Membrane fastened/bonded to temporary/enabling works Inner skin Basement Basement (d) External (reverse) waterproofing (h) Drained cavity. 14 . Continuity of waterproofing between the junction of the superstructure and the basement walls Figure 8: Continued must also be assured (Figure 11). The system will generally need to be continuous around the basement walls and (g) Drained cavity with integral protection and external floors (Figure 10) and extend at least 150 mm above (reverse) waterproofing ground level. The final choice depends on the site drainage system conditions and the level of waterproofing necessary. Some systems may also make use of externally applied Inner skin geocomposite drainage sheets to prevent or lessen hydrostatic pressure reaching the external structure or waterproofing system (Figure 9). Basement (e) Drained cavity with integral protection Protection (if required) Geocomposite drainage sheet Preformed cavity (alternative to drainage system granular backfill) Membrane Basement structure Inner skin Water-resisting structural wall to BS 8110 or BS 8007 as appropriate Percolating External or internal ground water Basement waterproofing as appropriate (f) Drained cavity with integral protection and external waterproofing Enabling works Preformed cavity drainage system Membrane fastened/ Perimeter drainage (fin or land drain bonded to temporary/ to discharge water to downside) enabling works Water-resisting structural wall to BS 8110 or BS 8007 Figure 9: External drainage as appropriate Inner skin To be effective. The effect foundations have on achieving continuity in the waterproofing system must be assessed (see Founda- External or Internal tion design on page 12). Basement structure DPM Figure 10: Continuous waterproofing to basement Continuity of waterproofing with DPM External waterproofing Basement slab with drainage as required DPC Cavity Horizontal Airbrick tray waterproofing with protection where required (a) External waterproofing Consult with External manufacturers waterproofing for specific detail (a) Linking of external waterproofing with DPC/cavity tray Continuity of waterproofing with DPC and DPM DPM Inner loading wall Cavity tray Airbrick Waterproof membrane Cavity fill (no wall ties) DPC Loading slab to resist hydrostatic pressure External drainage as required Internal Consult with waterproofing manufacturers for specific detail Fin drain (b) Linking of internal waterproofing with DPC/cavity tray (b) Sandwich construction Figure 11: Continuity of waterproofing . Details to cater for steps in the waterproofing as required foundation can be produced as in Figure 12.step changes in superstructure construction 15 .linking with Figure 12: Continuity of waterproofing . any water penetrating the outer leaf is to falls with drainage provision intercepted by the cavity and discharged below the slab level. it would be acting as a cavity- drained system. The service itself must also be waterproofed sloping site. therefore. they must Figure 12: Continued be properly detailed. (d) External waterproofing of projecting basement roof Preference should always be given to taking services up and over the walls to avoid penetrating the basement walls below ground. Details will vary according to the category and size of the penetration and the waterproof- Discontinuity can sometimes be acceptable. 16 . with every case. Discontinuity of the waterproofing system must. The wall ties would therefore need to be omitted and the inner leaf designed as a loadbearing Continuity of single-leaf wall. decided for the project in hand. If holes are unavoidable. DPM DPC Weepholes Inner waterproofing or Stepped DPC Airbrick cavity drainage system DPC with sealed laps Inner loading wall and slabs as required Inner blockwork Slab may require Fin drain to a DPM which may intercept surface water need bonding to DPC (alternative to pipe and aggregate drainage) Waterproof membrane with protection board Reinforced masonry wall (c) Internal waterproofing Airbrick for ventilation Suspended slab Chamfer to discharge water Weepholes Fin drain or land drain to discharge to downside Figure 13: Discontinuity of waterproofing on free draining site Cavity Continuity of waterproofing tray with cavity tray Discontinuity of waterproofing is possible here because any water rising by capillary action is effectively prevented from reaching the inside face of the inner leaf. Appropriate floor details would also waterproofing with DPC and DPM have to be adopted. Such construction cannot be used where the water table is high or variable. as water could build up within the cavity and rise above slab level. no outer waterproofing. and waterproofing to the top of the retaining wall. Avoid using general The detail is shown with the inner leaf tied to the outer manufacturer’s details as they are most unlikely to suit leaf. as shown in ing system being used. This is possible only with certain constructions on sloping sites or in freely draining soils with a low water table. be considered only where the ground and structure are able to prevent water ingress. free-draining flat site. they must The Figure also shows the necessary ventilation of the be discussed with the manufacturer and specific details cavity. Discontinuity may also only Projecting basement roof be acceptable where natural gases such as methane and radon are not present. Roof area to be laid In addition. Nor is it feasible with soils of low permeability on a flat site. This is not a cavity drain system (Type C) but in effect a Type A construction that can Because of the variations between different waterproof- intercept water finding its way through the outer leaf. The detail could also he appropriate on a into the service penetration. Where the cavity is to be the main intercept. ing systems and type and form of service. Figure 14 shows a typical Figure 13 where a masonry wall is detailed for use on a approach. Continuous waterproofing system. depending on the prevailing soil condi- tions as learned from the site survey. positions. the appropriate systems must be combined and considered An example of a degree of upgrading of a Type A together. and would be effective under in the selection process. the low permeability might cause a Note: Service penetrations below ground should temporary perched water table. Figure 15 is provided to help against water ingress. Their expertise will help ensure success. At the extreme. tion with the waterproofing manufacturers. but with additional ventilation or dehumidification. a Type A construction with drainage might not be Selection procedure acceptable without further upgrading. if a variable water table stays high for some Figure 14: Service penetrations through waterproofing time. However. the The broken lines represent the maximum acceptable risk cost of which may be influenced by the initial type of and therefore the minimum acceptable construction for construction and the external soil conditions. Such upgrading could involve internal waterproofing or the creation of a To ensure that the risk of moisture penetration is kept to drained cavity. The position of the line within the box is an attempt to further quantify the risk. it was shown at the certain ground/soil conditions (see Waterproofing details beginning that choosing and specifying a waterproofing on page 13). the design team should now be able to decide tional cavity wall provides a secondary means of defence the waterproofing strategy. Similarly. it may be possible to modify a basic construction to make it Guide to assessing basement designs suitable for a more severe situation. so creating in effect a be avoided wherever possible variable water table or hydrostatic pressure on the wall. It is therefore most desirable The above shows the significant effect that the water that the manufacturers of the likely systems are contacted table has on the selection process. For example. Figure 15 gives general guidance on the suitability of A Grade 3 or Grade 4 environment can be achieved by various forms of construction under differing water table using a similar construction to that required for Grade 2. an acceptably low level for the life of the structure. A line running through hydrophilic strip or crystallisation a box indicates a variable risk of acceptance and coating unacceptance. the prevailing water table. Type A Type B Type C No integral protection Water-resistant concrete Drained cavity Water table Plus Plus Plus BS 8110* BS 8007 Waterproofing drainage BS 8110* waterproofing BS 8007** waterproofing Plus moisture barrier Low (soil permeability may affect risk) Variable (subject to prevailing soil conditions) High Decreasing risk * Design to 0. in consulta- early. and how. quantified additional membrane by the variation in depth of tint. system is a specialised task. Having completed the investigation already construction is given in Figure 13 in which a conven- outlined.2mm crack widths except for low hydrostatic head ** Alternatively design to BS 8110 with 0.2mm crack width for low or variable hydrostatic pressure Figure 15: Design assessment guide to assessing designs for basements 17 . thus behaving like a permanently high water table. Constructions to the right of Alternative or Waterproofing the broken lines have progressively lower risk. a Type A Any service within construction with waterproofing in a low water table is penetration will also likely to provide an acceptable solution in many soils but need to be sealed may be unsuitable or require additional drainage or waterproofing in soils with particularly low permeability. then conditions are the least severe. when continuity is not possible aggressive chemical. The least If the water table is permanently above floor level. the structure waterproofing positioned and placed against the must still to play a major role in keeping out water. If pumps or drains fail. Assessing risk Permanently high water table Ground conditions dictate the options available. If outside face of the main structure moisture ingress is too rapid. the design team has an almost free hand to is higher. However. leaving the design the water table. there is a All other factors discussed under Variable water table risk of a perched or variable water table . The severity falls be installed to lower the water table permanently. This is because the water exerts a permanent choose the most appropriate form of construction and pressure on the structure. the cavity is more likely to External(reverse) Where the waterproofing is positioned be unable to cope with the water.and therefore apply. To reduce risk. surrounding air Where groundwater contains aggressive chemicals such as sulfates. If natural gases are present. consider incorpo. consider applying a suitable external protective than air dry membrane. With low-permeability soils such as some clays. if there is any doubt about the long-term effectiveness of the drainage system. if a drainage system can leave the design team with very few. An alternative would be a water-activated submersible Glossary sump-pump taken below the lowest slab level. only a Type B or Damp-resistant Having a high resistance to moisture C construction can be considered to carry an acceptably penetration low level of risk. Type C construction should include an externally applied membrane to Hydrostatic head Water pressure. With Type B. a Type B construction should consist of a High water table Where the water table is above the suitably resistant concrete or have an appropriate underside of the lowest floor level externally applied membrane. the into three basic categories according to the position of severity is proportionally reduced. the waterproofing outside the main structure but placed method of getting the ingress water away plays an against the enabling works important part in assessing the risk. Generally. the risk is increased Permanently low water table and the structure must be considered to be in a category If the water table is permanently low. do not lose sight of the moisture fact that the water-resistant structure must remain the first line of defence against water penetration. for example. the most severe category. not permitting moisture to enter Variable water table If the site cannot be drained and the water table rises Damp resistance The ability of a material to exclude occasionally. the nature of the risk is hydrostatic head. the concrete must be able to withstand the aggressive chemicals. equivalent depth of water 18 . In the same as for a variable water table except that the risk this situation. specialist advice nently low water table. a back-up waterproofing system. In addition. expressed as an protect the structure. However. while the most severe severity is increased. However. although variations can occur within team with the same options as given above for Perma- them. This may also be considered on a normally free-draining site to Air dry When the surface humidity of a material is equal to that of the ambient cater for unexpected adverse conditions. External Where the waterproofing system is When a Type C construction is selected. the choices are reduced to Type A or B Combined system Two or more waterproofing systems construction in consultation with the membrane manufac. then a second. Such drainage could. Free-draining Ground through which free water rapidly drains away If the groundwater contains aggressive chemicals such as sulfates. the severe give the most options. If in The condition of a material when wetter Damp doubt. consist of land drains discharging to the downside on a sloping site. should be sought. waterproofing system should always be considered. If the water table remains high for long Expansion joint Joint that permits relative movement periods. Drained cavity A continuous cavity which intercepts and When selecting a Type B construction. for example in with an external membrane capable of resisting the concrete. Just how severe moisture depends on how high and for how long the water table rises. Damp-proof Impervious to moisture. the severity is increased. drains away incoming water rating some form of waterstop in construction joints (see Figure 2). used together turer. in these circumstances. of water pressure against the structure . water is likely to enter the basement. back-up waterproofing system caused by expansion and contraction due to changes of temperature or could be considered. significant risk of percolating water building up a In this.unless adequate drainage can be provided. the structure should be tanked Construction joint Joint formed in-situ. If Type A is used. and there is no of either variable or permanently high water table. Approved liquid Document C. cast above floor level to position wall or column (2) BRITISH CEMENT ASSOCIATION & BRITISH STRUCTURAL formwork for the next lift WATERPROOFING ASSOCIATION. 1981. viability and costs. C/10). 429 pp. NHBC Standards. Clause 13. Amersham. Crowthorne. (Ref. permeability of the soil.5 'Damp proofing' gives guidance penetration on the application of tanking to existing walls in base- ments. Vapour resistance The ability of a material to resist vapour NATIONAL HOUSEBUILDING COUNCIL. retaining walls and ground stability. Low water table Where the water table is permanently (5) JACKSON. 1991. British Cement Association. BS 5930 : 1981.g. Water-resistant Having a high resistance to water Section 13. BCA.1 'Siting of dwellings' reviews items to be Vapour-resistant Excludes water and has a high resistance taken into account when developing sites. Water vapour Water in its gaseous form 19 .059) construction formwork in position. concrete Chapter 5. Vapour check A continuous vapour-resistant layer BS 8301: Code of practice for building drainage. 1992. percolating water is held above the underside of the Other publications relating to basement lowest floor level. Zurich Municipal. Digest 369. 1991. Relevant areas to vapour penetration include waterlogging. masonry below DPC and tanking discontinuity or joint in site-placed materials. Farnborough. water Garston. BSI. (Ref. 10 pp. (7) DEPARTMENT OF TH E ENVIRONMENT AND TH E WELSH Moisture Water in the form of vapour as well as OFFICE.3 'Drainage below ground' includes guidance on groundwater drainage. not permitting water to penetrate ZURICH MUNICIPAL.. waterproofing between the two non-tied leaves of the BS 8110: Structural use of concrete. HMSO.finding the hazards' gives the underside of the lowest floor level guidance on the identification of hazardous site condi- Water Water in its liquid form tions which need to be considered (e. level 1988. Kicker Small concrete upstand. 8 pp. BR211. 37 pp. Basingstoke. eliminating a kicker (3) BUILDING RESEARCH ESTABLISHMENT. because of insufficient moisture. 48.1 'Substructure and ground-bearing floors' Waterstop A product or system. N AND DHIR. Waterproof Impervious to water. Chapter 3. to includes guidance on habitable rooms wholly or partially prevent the passage of water through a below ground level. Low-permeability Resistant to water penetration 148 pp. Code of Practice for site investigations. Part 1: Code of main structure practice for design and construction. 1991. penetration Vol. Site preparation and resistance to Perched water table Where. 1. BS 8102: Code of practice for protection of structures Sandwiched Where the waterproofing system is against water from the ground. resulting in hydrostatic pressure structures BRITISH STANDARDS Protection layer An element used to provide protection BS 8007: Code of practice for design of concrete to a waterproofing system structures for retaining aqueous liquids. Loading coat A material applied to the waterproofing 1992.benefits. Macmillan Education 4th Ed. Variable water table Where the water is occasionally above Chapter 4. The Building Regulations 1991. Basement waterproofing: Site guide. membrane to enable it to resist hydrostatic pressure (4) BRITISH STANDARDS INSTITUTION.Hydrostatic pressure The water pressure exerted as a result of a hydrostatic head References Integral protection Where the structure itself provides the (1) BRITISH CEMENT ASSOCIATION. BRE.1 'Foundations . 23 pp. R. groundwater). water Slough (now Crowthome). Radon: guidance Membrane A material which forms a continuous effective barrier to the passage of on protective measures for new dwellings. NHBC. Waterproofing The total method or combination of Section 3 'Damp proofing' includes requirements and system materials used to create a waterproof protection guidance on subsoil drainage to prevent waterlogging. Building guarantee technical manual. Garston. BRE. (Editors) Civil engineering below the underside of the lowest floor materials. (6) BUILDING RESEARCH ESTABLISHMENT. Chapter 5. Interstitial condensation and fabric degradation. Kickerless A mechanical means of retaining 20 pp. London. 1994. and on the application of basement tanking. Options for quality in necessary protection to the passage of housing: Basements 1: . Parts 1-5. placed in-situ. 1994. London. 058 British Cement Association .8 : 699.BASEMENT WATERPROOFING: DESIGN GUIDE CI/SfB UDC 643.82 BRITISH CEMENT ASSOCIATION PUBLICATION 48.