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. 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. 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 . and then immediately falls again. 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. penetration through external waterproofing and then ronment would be acceptable. 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. construction Type A/B/C tion may occur. Selection of waterproofing system Design principles The specification of waterproofing systems is a special. it is important to identify it. and his customer to Construction options on page 10). 2 . 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. tant. If it did become neces- provides more stable construction. 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. and other areas where the performance level permits no water penetration. is thermally efficient sary. since usage through the structure is less than if the water table stays may change. Is construction ised task. However. in the flow chart in Figure 1. However. be regarded as difficult and possibly uneconomic to build on. after heavy rain tion. High water tables present the greatest risk of failure of the water-tightness of a basement. required in a domestic situation. How often and levels to basement usage. It is recommended that. Grade 3 environment than to upgrade it later. If there is a perma- nently high water table. a few points need to be considered when selecting the form of construction These and other factors needing consideration are shown and waterproofing system. Some basements may be for . in particular. which is Grade 3. but higher levels of Basement water vapour would be tolerable and surface condensa. shape considerations Foundations The Grade 2 environment is for use as workshops and design plant rooms. as defined in BS 8102. The British Structural Waterproofing Association Solution can provide details of manufacturers of the different generic waterproofing systems and of appropriate specialist waterproofing contractors. This publication is intended to help the builder or designer arrive at the most appropriate form of construc- tion and waterproofing solution. It is unlikely that a Grade 4 environment would be Including a basement maximises available land space. which are appropriate for residential Design House type and basements. Basements can be economically internal waterproofing. benefit by being offered houses with greater potential(1). Basement waterproofing: Site development Environmental guide(2) provides advice on the application or installation requirements of the various waterproofing systems.say. If the water table rises briefly . once the design team No buildable? has given the system some thought. the risk of water permanent workshops or garages. A basement performing to Grade introduced onto most sites and. it is better to construct a basement to a high for a much longer period. Most basements will be for domestic accommoda. and defines them in Grades for how long the water table stays high are also impor- 1 to 4. 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. and comments on other associated construction matters. Proposed Basement use A companion publication. The Grade 3 environment is for ventilated residential and working areas which require a drier environment. 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. and a Grade 2 envi. the manufacturers of the systems under consideration are contacted immedi- Yes ately for early advice and help on the waterproofing design. 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. purposes. In addition. External Sandwiched Intenal waterproofing waterproofing waterproofing Type A structures . B and C.drained protection Figure 2: The three forms of basement construction 3 .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. 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 . Type A. These are shown diagrammatically in The existence of any aggressive elements in the ground Figure 2. together with the and/or the groundwater must be established to ensure factors affecting their choice.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 . hydrophilic. any lowering of Deciding on form of the water table will need to maintained until the loads acting on the basement. from either itself or in combina- construction tion with the superstructure. and discussed overleaf. The main contractor may need to lower the water table temporarily to enable the construction and waterproofing to go ahead.tanked protection External or internal Crystallisation. then an internally applied membrane may be would be carried out according to the recommendations easier to maintain. the water table is consistently below the level designed to be water-resistant. basement structure must be designed within certain strict for example. finally entering the basement as free waterproofing system. The proofing system used. These include natural groundwater as an integral shell. which give guidance on the grade found and repaired. water vapour movement. any defects will allow water to pen- pointing to produce a surface good enough to accept a etrate the structure. also provide high resistance to Since total reliance is placed on the waterproofing system water vapour movement. in practice. consideration must system must be able to withstand hydrostatic pressure always be given to what would happen as a result of any from groundwater. which depends upon through lack of compaction. a permanent external in-situ pavement or parameters to ensure it is water-resistant. Type C (drained protection) structures incorporate a drained cavity within the basement structure. 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. 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. water. dampness. also provide high resistance to longer it stays high. this form reduce the risk (see Assessing risk on page 18). There is Where the site is permanently free-drained. or is liable to be. 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. cracking due to be the same. natural drainage and soil type. severely restricted by. 4 . in Type A structures. If the water table is high only briefly. However. logged conditions. reinforced or plain concrete or masonry with the structural waterproof. where the levels may vary the two extremes described above. using a concrete of low permeability. the ingress might not be enough to show itself. by far the The most common defects are permeable concrete most significant is water table level. with an integral construction or external system to Without the addition of a separate membrane. These can all be as follows: reduced by correct specification and design and by • Athe high or perched water table where. or free-drained site. any Structural walls may be prestressed. depending on the water. The watertightness of the Type A basement relies totally Or it may be applied internally to the finished basement. additional waterproofing systems may be applied either internally or externally to of the basement floor. Most designs patio. If this is not so. the cavity system may not With a varying water table. However. Where the defect is small. the Where access is. If this water is not removed. therefore. 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. Type B structures need to be carefully constructed to of the basement floor. The chosen structural waterproofing pass through it. they can be generally classified thermal contraction and shrinkage. However. nants. basement types are discussed below. 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. groundwater contami. 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. depending on the water- proofing system used. avoid defects that let water through. the greater the risk of significant dampness or even partial flooding. in some dampness in the structure. but will not necessar- ily show itself on the internal surface. Of these. the faces of the walls and floors to control water vapour • Abetween variable water table. the basement will fill to the level of the water table. The structural wall may be prestressed. where appropriate. With a Masonry walls may require a cement rendering or flush high water table. levels or perched water tables. Type A ing system incorporated externally during construction. An internal system could be used of concrete and steel spacing. This form of construction can. reinforced or plain decoration or surface coating that acts as a vapour check concrete or masonry. The effects of water table conditions on the three service loading. Defects can then be more readily of BS 8007 or BS 8110. Although they are • where A permanently low water table. to the substrate wall can add further complications. affected by the attachment of skirtings etc. movement. or by fittings applied subsequently. Externally applied Type B (structurally integral protection) structures systems will require subsequent excavation. honeycombed concrete. many factors and no two sites can. many factors need to be reliant upon the design and construction of the basement known (Figure 1). groundwater level is consistently above the level careful construction. 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. This Form of construction can. be said to contamination of construction joints. by definition. or to provide further protection. on the effectiveness of the waterproofing system. this will usually result sump for removal by drainage or pumping. together with any superimposed or defect. Invariably built of reinforced or prestressed concrete. and appropriate joint details. account must be taken of the need to gain access if a defect occurs. If the soakaway silts up or the drain concrete. Hybrid systems . (The design of the structure Bonded sheet membranes are generally cold-applied or heat-bonded to the finished structural walls. 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. 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. great care is required in the placing and Type C) could be considered to carry the smallest risk of compaction of the concrete. say. to the pouted ing surface water. can arise in several ways: toppings and coatings • flooding. Additional waterproofing protection may be used. An alternative method of failure. 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. The back is completely retaining but the front is not. 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.must be avoided because of the danger of incompatibility. and conditions. Remedial action can usually be carried out from the and executed. It is imperative that all continuous and stopping these is usually fairly straightforward. minor defects in the concrete properly selected and adequate for the proposed location usually result in only small amounts of water penetrating. Type A structures are not recommended in areas with an undrainable high water table. all three forms of presence of water to seal the joint. placed against the structure. • 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.) applied externally. 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). formulated pressure-sensitive adhesive. sloping or vertical waterproofing be specified. construction carry little risk of damp penetration. Both are should allow for clearing of silt and rodding of drains modified bitumen on a range of carrier films. 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. they need to be restrained resistant to the ingress of water under a hydrostatic head.using one system with another . unless not mix hot and cold systems. or internally with a loading coat strong enough to resist hydrostatic pressure. but On a free-drained or sloping site. 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. Design considerations Suitability of construction forms • shrinkage Flexible and able to adapt to minor movement and within the substrate Generally. it is rare for a defect to be so British Standards. the water table stays high for a long time. dampness on the internal surface becomes a possibility. Most proprietary systems and materials are covered by In a free-draining site. Do Variable water tables present less of a problem. a Type B construction with the areas most commonly associated with leaks. the designer must ensure the materials are With a high water table. the cavities may be led subsequently fully bonded by means of a specifically to a soakaway to handle any ingress from. They are should blockages occur. Composite An increase in the ingress of water could exceed the polymeric sheet membranes are also available. inside.Construction joints need particular attention as these are With a very high water table. horizontal. Since reliance has often to be placed on the waterproof- ing system. 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. Category 5: Mastic asphalt membranes Category 6: Cementitious crystallization active systems With a permanently high or variable water table. attached to the enabling works (reverse tanking). They are drainage capacity and result in dampness or flooding. so avoiding the need for external excavation. 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. percolat. but defects in • Generally. Agrèment certificates or manufacturers’ serious that water comes through by capillary action. for example on sloping sites where the polyethylene sheets. becomes blocked. in one proprietary waterproofing system. A Type C construction could provide a suitable form of Category 2: Cavity drain membranes structure. and on the initial resistance Category 4: Liquid-applied membranes of the structure to water ingress. where any water can be easily drained to a Cavity drain membranes are high-density dimpled convenient point. dimples form permanent cavities between the structure 5 . warranties. 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. When appplied can protect against and groundwater 6 . e. 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. toppings and vapour barrier in Type B construction. they assist repair of local defects • The substrate does not need to be dry before • Applied externally. must be restrained by a • Easily applied to difficult substrate profiles loading coat if subjected to a hydrostatic water pressure.g. 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. All • Easily applied to difficult substrate profiles are designed to be used inside the structure but can be • Elastic and flexible. but retain a degree of flexibility. mastic liquid. generally in two coats as a bitumen solution. • 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. coating are applied as a layer(s) to form a dense. unless used as a Proprietary cementitious multi-coat renders. waterproof membrane. When the clay meets water. If internal. renders or mortars. They are used internally to drain Category 5: Mastic asphalt membranes and control water ingress. they block can swell to many times its original volume. They cool to a hard. they maintain continuity of membrane coatings are premixed slurries applied as a thin layer.or two-part systems. it free lime in concrete. sealing any cracks and capillaries. Mastic asphalt membranes are applied in three coats as a hot. In the latter case. 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. Waterproof renders or toppings Design considerations consist of a layer or layers of dense cementitious material incorporating a waterproofing component. thus accommodating minor movement and shrinkage within the structure external. the loading coat must be strong multi-coat renders. honeycombing They are applied cold. gaps or voids in the membrane. piles and ground beams • before Requires protective screed on horizontal membrane loading coat is installed • With high or variable water tables. and the internal shell. such as Liquid-applied membranes are one. Application can • Installed after the construction of the basement be external or internal. • Minimum preparation of substrate needed Design considerations • There is no hydrostatic pressure on the system: water • defects Because of the multiple coats. toppings and coatings enough to resist hydrostatic pressure. 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. as in Type A construction • When applied internally. elastomeric urethane or modified Category 7: Proprietary cementitious epoxy. the loading coat must • Defects may he rectified before completion be strong enough to resist hydrostatic pressure. may protect against aggressive application soils and groundwater • Minimum preparation of substrate is required • Will not self-seal cracks greater than hairline (0. waterproof Design considerations coating. This category of membrane is used externally. They can be applied both externally and inter- nally. By reacting with biodegradable cardboard. They can be applied against existing waterproofing already given.in both new and remedial work . if vertical protection and drainage are required. 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. Membrane protection products movement construction and contraction joints. 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 . according to the location and sealed. The tube is then cast into the construction joint. The strips may be wholly of hydrophilic Other design considerations material. 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. However. 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. These products are not suitable for use in low water absorption and be frost resistant to prevent expansion joints. Protection boards should be rot-proof and robust enough to withstand site operations. Alternatively. This can is movement. construction and contraction joints. it flows freely out of the perforations into any function: cracks. Profiles If construction operations may damage applied mem- incorporating a centre bulk or box are used where there branes. can cause problems when the concrete is being placed and compacted. in basement walls . fillers and chemicals to be further insulation to comply with the Building Regula- mixed on site as a slurry. These rear-fixed proofing system. material or filler. 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. The depending on whether it is placed inside or outside the waterstopping action results from salt crystallization. • inStrips or profiles of hydrophilic materials which swell water. when the exit of the tube is the following types. Any external insulation must have the concrete. The slurry is applied to the face tions However. certain aspects are common concrete since they avoid the problems of breaking out to several systems. site-placed concrete. the joints or discontinuities within a concrete structure. or compounded with a rubber. 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. 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. as in expansion joints. 7 . bonded across the joint Rubber or flexible PVC waterstops with a suitable adhesive. they are best avoided. waterstops may be cast totally within the supplied by most membrane manufacturers may be used. or part of a As well as the general characteristics of the categories of composite profile. 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. Plain web profiles are available for non-moving or low. where insulation is required. 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. adequate protection must be provided. Internal waterstops will protection.bandage • Post injected systems joint systems may be used. 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. These consist of strips of synthetic polymer membrane. it may - of the first-poured concrete before the second pour. Alternatively. They are available as strips for bonding or nailing to the first-placed concrete immediately before the second pour.dictate the form of construction and the presence of water. of the structure since the lower basement slab is more efficient than a slab at ground level.• substrate Being rigid. The • Rubber or flexible PVC extruded profiles injected material then sets to seal all water paths through the joint. face in which they are installed. fissures or holes in the construction joint. As systems vary. consist of vertical blockwork and a 50 mm screed to horizontal surfaces. These are known as internal or They are more convenient since they provide immediate centrally placed waterstops. or protruding from underneath it. as they are more difficult to install and after laying. 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. within the pores and capillaries of waterproofing system. The final selection will depend on the to install a conventional rubber or PVC waterstop. loss of its thermal insulation properties. Water vapour tends to move from areas of high vapour pressure to low vapour pressure. If the environment is controlled solely by natural air movement. since the materials used and the also act as an effective vapour check. water vapour will move. They are therefore generally more System restraint prone to condensation. and there can be problems in locating defects in applied externally can cause interstitial condensation (3). Condensation determined and the membrane manufacturer must be Because window areas are often reduced. Defects in the materials or in their A system that acts as a vapour check can be advanta- jointing may require remedial treatment. low rate as to be of little consequence. the structure provides the restraint. 4 and 5 are employed internally. a basement are controlled by properly designed heating However. Access following construc- effect that the waterproofing system has on the resistance tion may not be desirable or possible. Evidence of a flooding site could suggest their precise nature and concentration must be an impermeable soil or a high or perched water table. 3. “Investigation of the site is an Vapour control essential preliminary to the construction of all civil engineering and building works”. therefore. Categories 1. there tends to consulted. in which case an to water vapour. methane and other gases. with the product.see Condensation above. Reference 3 explains how to estimate its space within the structure. The site history and name clues such as “Pond with aggressive chemicals. used internally without a loading coat. it is far better to design the structure in a way A vapour-permeable waterproofing system can thus be that avoids expansion joints. careful consideration must be given to the watering would be required. so heating and air circulation Categories 1. 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. therefore. from within the structure Expansion joints towards the ground. Groundwater Water table Chemical barrier The existence of a watercourse or water table and its An external membrane can protect the main structure. systems that are not continuously bonded. categories 1 to 5 can important for basements. the performance of internal waterproofing and permanent ventilation. where internal conditions in internal waterproofing system may be preferable. this is not still control moisture ingress if the cracks are fine. However. the condensation risk increases and more care is needed in the choice of waterproofing and Site investigations insulation systems. In most domestic situations. 3. Lane” can help. As stated in BS 5930 (4). However. 8 . but will allow relative humidity within the basement to rise if the reverse conditions Defects and repair apply. It is important. When categories 1. Categories 3 and 6 are active systems and can ‘self-heal’. 4. permanently or for long periods. 4 and 5 need to be restrained so that need to be carefully designed to ensure condensation is they can resist the forces involved. Although this is performance of the finished structure will be greatly often seen as an advantage. When applied controlled. 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. Brief resistance of category 7 systems can vary significantly details of some of these aspects are given below. With externally geous if the vapour tends to move from the ground into applied systems. so. even years later. Categories 6 and 7 are more brittle with into the air. 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. In practice. although joints can be detailed to cater for movement. or by the application of subsequent fittings. if the water table is low. some structures need to influenced by the ground conditions. It is often the basement but similarly will allow the relative humid- difficult. They will crack if the substrate cracks but may always pass from the ground into a basement. by the attachment of The advantages/disadvantages of vapour permeable/ skirtings etc. 5 and 7 rely on their impermeability to control water ingress. 6 and 7 can be risk and effects. low strain capacity and so are less tolerant of structural Although it is commonly thought that water vapour will flexing. the condensation risk can be systems can be affected. be less natural ventilation in basements than in other areas of a house. in which case a to be assessed and reference should be made to BS 5930 category 6 or 7 system will be needed. 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. If the water table is high. This will take up in detail here. to reach defects in externally applied ity to rise if the reverse is true. The vapour for detailed information on site investigations. if the ground or groundwater is contaminated lished. they need Condensation in basements is too complex to be covered to be restrained by a loading coat. as indicated in Characteristics of reduced to be no worse than in the rest of the dwelling. advantageous if the vapour tends to move from the inside to the ground. to decide whether water vapour needs to be controlled or not . impermeable systems are then usually negligible. since ground de- In general. Categories 2. Several factors need allow for water vapour movement. a vapour check systems.. This is particularly As well as controlling water ingress. this may mean excavation. externally. construction forms on page 4. seasonal position below ground will need to be estab- However. 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. little or no fines Coarse soils and other materials Grave1 with fines.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. silty Fair to practically Almost none to sands. elastic silts Soils having high Practically impervious High Clays (inorganic) of compressibility high plasticity. soft rocks. rock flour. etc. clayey gravel. impervious slight poorly graded gravel-sand-clay mixtures Well graded sands and Excellent Almost none gravelly 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. Excellent Almost none hardcore. Other materials Soft: chalk. Excellent Almost none little or no fines Sands with fines. 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 . silty Fair to practically Almost none to gravel. clayey sands. 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. Fair to practically Almost none to rubble impervious slight Well graded gravel and Excellent Almost none gravel-sand mixtures. impervious medium poorly graded sand-clay mixtures Silts (inorganic) and Fair to poor Slight to medium very fine sands. which tend to be be effectively drained. they may not be appropriate because of the difficulties of maintaining watertightness. giving the dwelling an elevated aspect. for three types of site: sloping. although expansion joints are a common solution. The remains of former buildings or structures on the site need to be assessed. water tables. mineral oil shales. tanked basements or Type C structures can therefore be Table 1. provisions. Reference 7 gives information on site preparation and resistance to moisture. Cut-off drain Movement risks likely to affect basements A change in ground moisture content . such as peat Flat sites provide the opportunity for basements wholly and sulfates. 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. and other fill materials. adapted from reference 5. particularly where large amounts of organic matter have been buried. Some soils contain chemicals that may harm both the structure and the waterproofing system. and includes guidance on ground contaminants. gives the characteris- built. which should be assessed before proceeding further. For example. radon and methane should be ascertained. movement joints should be considered. Excavated material may be re-used to landscape around basements partially The presence of. and guidance for its control may be draining or is in an elevated position with drainage found in reference 6. in particular.caused. or potential for. its drainage characteristics. flat and infill. the prevailing terrain.can result in ground movement and affect the loadbearing capacity of soil. Although such matters can be catered for structur- ally. 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. 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. Check the Flat sites ground for materials that are detrimental. Methane and other gases are likely to be linked to infill and made-up ground. proximity of adjacent buildings and the should be established. They are best removed to avoid differential movement due to bearing over strong points. Perimeter drain to discharge to downside If the risk of movement is high. by the removal of trees . 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. 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. Free-draining soils and-fill options (Figure 3). Figure 3: Basements on sloping or elevated sites 10 . designers should not (b) Split-level dwelling attempt to create waterproofed expansion joints. properties would be at little risk impermeable. with cut- water reaching the basement wall. drainage provisions. Design drainage to reduce local groundwater pressures. but instead should design discrete boxes that can be sepa- rately waterproofed. for example. their positions on. Where possible. for example. Any new construction proposals requirement of the end user. simply designed in concrete or masonry. Steeply sloping sites may have high land-slip risks. they do present problems. particularly in a waterlogged site. Economical Type A soil type and. to determine the from percolating groundwater. Particular care is needed where there are changes in the Cut-off drain soil strata that may cause differential foundation move- ment. Some slags and other residues often contain toxic materials and some furnace ashes may be reactive. forms and waterproofing methods will therefore depend If there are any drains or land drains. with tics of the main soil types. Since these sites can normally present fewer problems than clays. natural gases such as below ground. Such sites can also present risks from acid wastes. therefore. or partially below ground (Figure 4). soil conditions. It is important. with a drainage sump (Figure 5(b)) for rain- water. Design preference is for Type B construc- tion. 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. this form of construction can be adopted Perimeter drain to for both flat and sloping sites. Alternative systems should therefore be looked at. 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 . Basements constructed on a flat site in low-lying areas with impermeable soils can be difficult to drain. Semi-basements on infill sites can probably use a bunded catchment area. the bund walls should be designed as Type A tanked construction or Type B water-resistant Cut-off drain concrete. Where adjacent properties have to be underpinned. fluctuating or perma- nently high water tables. Any window fire exit must be above the highest anticipated water level. Clearly. However. substructures designed in water-resistant Type B construction would therefore be advisable. As there may be problems with perched. Cut-off drain Infill sites Inner city areas provide more opportunities for house basement construction because high kind values increase property costs. If so. it can be difficult to achieve continuity in external or pre- applied waterproofing systems. Infill sites between adjacent dwellings can be developed (Figure 5). perhaps with internal waterproofing or drained cavity provision. to achieve continuity of waterproofing. 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. since they are points of weak- an additional escape for water. ness and need a lot of attention to detail. as with a clay soil. the designer should The orientation of the basement area to the general flow consider 'buildability' and the acceptable level of risk.see Figure 6. The outlet from such Complicated foundation designs do not lend themselves pumps must discharge to areas where the water cannot to external waterproofing. should be provided and graded to storm drains or open outlets on the downside of the building. but may not be appropri. When deciding on the form of feed back to the pump inlet. construction and waterproofing. 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. for external relief drainage proofing (see Waterproofing details on page 13). Expansion joints and complicated taken for design. 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 . ate for all water-proofing systems. Where basements are Common foundation designs are shown in Figure 7 with constructed against the flow of water.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. (c) Staggered foundations An additional water-activated pump may be used to deal with run-off water. sub-drainage suggested waterproofing options. which are normally installed outside the structure. Any L. 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. 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. so improving the total water. risk of hydrostatic pressure. Such pumps. of groundwater should also be considered . relative to cost of achieving the desired performance. They can be used either to extend the application of Type A and B construction or to provide shapes are best avoided. 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. 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. The principal details and Difficult to achieve continuity elements of the main waterproofing systems are shown of waterproofing membrane in Figure 8. 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 . 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. 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. all laps in the waterproofing system must Basement be fully weathered and sealed. Continuity of waterproofing between the junction of the superstructure and the basement walls Figure 8: Continued must also be assured (Figure 11). The final choice depends on the site drainage system conditions and the level of waterproofing necessary. 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. 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). no waterproofing to walls. 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. each waterproofing system may be used as the sole protection or combined to give addi- Preformed cavity tional protection. 14 . structure not providing Type B standard Figure 8: Continued Water-resisting structural wall to BS 8110 or BS 8007 as appropriate As already indicated. 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 . The effect foundations have on achieving continuity in the waterproofing system must be assessed (see Founda- External or Internal tion design on page 12). as shown in ing system being used. no outer waterproofing. If holes are unavoidable. any water penetrating the outer leaf is to falls with drainage provision intercepted by the cavity and discharged below the slab level. be considered only where the ground and structure are able to prevent water ingress. with every case. Where the cavity is to be the main intercept. Details will vary according to the category and size of the penetration and the waterproof- Discontinuity can sometimes be acceptable. Such construction cannot be used where the water table is high or variable. Appropriate floor details would also waterproofing with DPC and DPM have to be adopted. free-draining flat site. Figure 14 shows a typical Figure 13 where a masonry wall is detailed for use on a approach. 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. Continuous waterproofing system. 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. they must The Figure also shows the necessary ventilation of the be discussed with the manufacturer and specific details cavity. This is possible only with certain constructions on sloping sites or in freely draining soils with a low water table. Roof area to be laid In addition. 16 . it would be acting as a cavity- drained system. decided for the project in hand. ing systems and type and form of service. they must Figure 12: Continued be properly detailed. Discontinuity may also only Projecting basement roof be acceptable where natural gases such as methane and radon are not present. and waterproofing to the top of the retaining wall. Nor is it feasible with soils of low permeability on a flat site. The wall ties would therefore need to be omitted and the inner leaf designed as a loadbearing Continuity of single-leaf wall. as water could build up within the cavity and rise above slab level. 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. Discontinuity of the waterproofing system must. The service itself must also be waterproofed sloping site. therefore. (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. 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 2.2mm crack width for low or variable hydrostatic pressure Figure 15: Design assessment guide to assessing designs for basements 17 . However. The position of the line within the box is an attempt to further quantify the risk. Their expertise will help ensure success. if a variable water table stays high for some Figure 14: Service penetrations through waterproofing time. 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. it was shown at the certain ground/soil conditions (see Waterproofing details beginning that choosing and specifying a waterproofing on page 13). system is a specialised task. a Type A construction with drainage might not be Selection procedure acceptable without further upgrading. it may be possible to modify a basic construction to make it Guide to assessing basement designs suitable for a more severe situation. but with additional ventilation or dehumidification. positions. Constructions to the right of Alternative or Waterproofing the broken lines have progressively lower risk. 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. 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. Having completed the investigation already construction is given in Figure 13 in which a conven- outlined. Figure 15 is provided to help against water ingress. 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. For example. the low permeability might cause a Note: Service penetrations below ground should temporary perched water table.2mm crack widths except for low hydrostatic head ** Alternatively design to BS 8110 with 0. the prevailing water table. Similarly. Such upgrading could involve internal waterproofing or the creation of a To ensure that the risk of moisture penetration is kept to drained cavity. tion with the waterproofing manufacturers. At the extreme. the appropriate systems must be combined and considered An example of a degree of upgrading of a Type A together. and how. and would be effective under in the selection process. A line running through hydrophilic strip or crystallisation a box indicates a variable risk of acceptance and coating unacceptance. in consulta- early. depending on the prevailing soil condi- tions as learned from the site survey. thus behaving like a permanently high water table. the design team should now be able to decide tional cavity wall provides a secondary means of defence the waterproofing strategy. an acceptably low level for the life of the structure. quantified additional membrane by the variation in depth of tint. so creating in effect a be avoided wherever possible variable water table or hydrostatic pressure on the wall. while the most severe severity is increased. a back-up waterproofing system. although variations can occur within team with the same options as given above for Perma- them. However. do not lose sight of the moisture fact that the water-resistant structure must remain the first line of defence against water penetration. consist of land drains discharging to the downside on a sloping site. 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. If natural gases are present. However. 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. specialist advice nently low water table. If the water table remains high for long Expansion joint Joint that permits relative movement periods. 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. Damp-proof Impervious to moisture. for example in with an external membrane capable of resisting the concrete. significant risk of percolating water building up a In this. and there is no of either variable or permanently high water table. Just how severe moisture depends on how high and for how long the water table rises. Such drainage could. the choices are reduced to Type A or B Combined system Two or more waterproofing systems construction in consultation with the membrane manufac. if there is any doubt about the long-term effectiveness of the drainage system. If Type A is used. drains away incoming water rating some form of waterstop in construction joints (see Figure 2). should be sought. in these circumstances. An alternative would be a water-activated submersible Glossary sump-pump taken below the lowest slab level. consider applying a suitable external protective than air dry membrane. the cavity is more likely to External(reverse) Where the waterproofing is positioned be unable to cope with the water. back-up waterproofing system caused by expansion and contraction due to changes of temperature or could be considered. If in The condition of a material when wetter Damp doubt. Free-draining Ground through which free water rapidly drains away If the groundwater contains aggressive chemicals such as sulfates. To reduce risk. Type C construction should include an externally applied membrane to Hydrostatic head Water pressure. With low-permeability soils such as some clays. External Where the waterproofing system is When a Type C construction is selected. However. Generally. then a second. In the same as for a variable water table except that the risk this situation. the design team has an almost free hand to is higher. surrounding air Where groundwater contains aggressive chemicals such as sulfates. the structure should be tanked Construction joint Joint formed in-situ.unless adequate drainage can be provided. the structure waterproofing positioned and placed against the must still to play a major role in keeping out water. If outside face of the main structure moisture ingress is too rapid. if a drainage system can leave the design team with very few. the most severe category. 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. there is a All other factors discussed under Variable water table risk of a perched or variable water table . of water pressure against the structure . the severe give the most options. leaving the design the water table. then conditions are the least severe. equivalent depth of water 18 . This is because the water exerts a permanent choose the most appropriate form of construction and pressure on the structure. Drained cavity A continuous cavity which intercepts and When selecting a Type B construction. In addition.and therefore apply. the concrete must be able to withstand the aggressive chemicals. waterproofing system should always be considered. expressed as an protect the structure. consider incorpo. 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. If pumps or drains fail. for example. used together turer. water is likely to enter the basement. the nature of the risk is hydrostatic head. the into three basic categories according to the position of severity is proportionally reduced. the severity is increased. when continuity is not possible aggressive chemical. With Type B. The least If the water table is permanently above floor level. The severity falls be installed to lower the water table permanently. Assessing risk Permanently high water table Ground conditions dictate the options available. 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. concrete Chapter 5. C/10). waterproofing between the two non-tied leaves of the BS 8110: Structural use of concrete. N AND DHIR. Low-permeability Resistant to water penetration 148 pp. Kicker Small concrete upstand. 1992. 23 pp. 8 pp. 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. and on the application of basement tanking. level 1988. eliminating a kicker (3) BUILDING RESEARCH ESTABLISHMENT. Relevant areas to vapour penetration include waterlogging. (Editors) Civil engineering below the underside of the lowest floor materials. Water vapour Water in its gaseous form 19 . penetration Vol. Variable water table Where the water is occasionally above Chapter 4.1 'Substructure and ground-bearing floors' Waterstop A product or system. Code of Practice for site investigations. (7) DEPARTMENT OF TH E ENVIRONMENT AND TH E WELSH Moisture Water in the form of vapour as well as OFFICE. not permitting water to penetrate ZURICH MUNICIPAL. Garston. HMSO. Approved liquid Document C. Amersham. 1991. Radon: guidance Membrane A material which forms a continuous effective barrier to the passage of on protective measures for new dwellings. water Slough (now Crowthome). Basingstoke. Options for quality in necessary protection to the passage of housing: Basements 1: . British Cement Association. 1991.benefits. 37 pp. membrane to enable it to resist hydrostatic pressure (4) BRITISH STANDARDS INSTITUTION. BS 5930 : 1981. (Ref. percolating water is held above the underside of the Other publications relating to basement lowest floor level.. 1. groundwater). BRE. 1994. Interstitial condensation and fabric degradation. Kickerless A mechanical means of retaining 20 pp.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. R. Chapter 3. BS 8102: Code of practice for protection of structures Sandwiched Where the waterproofing system is against water from the ground. Digest 369. (Ref. London. 1991. Vapour resistance The ability of a material to resist vapour NATIONAL HOUSEBUILDING COUNCIL. BCA.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. Low water table Where the water table is permanently (5) JACKSON. to includes guidance on habitable rooms wholly or partially prevent the passage of water through a below ground level. masonry below DPC and tanking discontinuity or joint in site-placed materials. because of insufficient moisture. 48.3 'Drainage below ground' includes guidance on groundwater drainage. 429 pp. 1994. cast above floor level to position wall or column (2) BRITISH CEMENT ASSOCIATION & BRITISH STRUCTURAL formwork for the next lift WATERPROOFING ASSOCIATION. Farnborough. Waterproof Impervious to water. permeability of the soil. placed in-situ.1 'Siting of dwellings' reviews items to be Vapour-resistant Excludes water and has a high resistance taken into account when developing sites.1 'Foundations .059) construction formwork in position. Site preparation and resistance to Perched water table Where.5 'Damp proofing' gives guidance penetration on the application of tanking to existing walls in base- ments. Vapour check A continuous vapour-resistant layer BS 8301: Code of practice for building drainage. Water-resistant Having a high resistance to water Section 13. BRE. BR211. NHBC. Parts 1-5. Basement waterproofing: Site guide. viability and costs. Part 1: Code of main structure practice for design and construction. (6) BUILDING RESEARCH ESTABLISHMENT. Building guarantee technical manual. BSI. 10 pp. Macmillan Education 4th Ed. Loading coat A material applied to the waterproofing 1992. NHBC Standards.g. 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. Crowthorne. Zurich Municipal. 1981. The Building Regulations 1991. London. Clause 13. retaining walls and ground stability. Chapter 5. water Garston. BASEMENT WATERPROOFING: DESIGN GUIDE CI/SfB UDC 643.8 : 699.058 British Cement Association .82 BRITISH CEMENT ASSOCIATION PUBLICATION 48.