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Newbuild Basements
Site Suitability for a BasementMost sites are suitable for a basement, but it is good practice to commission a geotechnical survey to ensure site suitability. Care should be taken if the survey reveals a permenantly high water table, a high probability of a perched water table or if the site is in a flood risk area. These problems would not rule out a basement but are likely to increase construction and waterproofing costs. In some cases maps or a site survey will show that there are power cables, sewers, or mains pipes running through the area where the basement is planned. These can often be moved, but in some cases the cost of doing so may prove prohibitive. On brownfield sites soil contaminants and ground gasses can present a problem. Fortunately, some waterproofing systems can provide protection against both of these. Basement Construction TypeIn virtually all cases, the basement slab will be formed of reinforced in-situ concrete. Typically, this is also used to form the basement walls, however other methods of construction can be used - e.g. precast concrete and insulated concrete formwork (ICF) filled with reinforced concrete. On large, commercial basement projects or where the basement is to be constructed close to adjoining buildings diaphragm walls or contiguous/secant piled walls may also be used. The choice of basement construction type will depend on a number of factors such as site conditions, cost, required performance, and the personal preferences of the designer. A simplified and evaluated design approach can be found in the Approved Document - Basements for Dwellings.1 Waterproofing Newbuild BasementsDeciding on the most suitable waterproofing system for a newbuild basement will depend on a number of factors including:
We would suggest that you contact our technical department on 01403 210204 to discuss waterproofing requirements for specific basement projects (alternatively, fill in our enquiry form). However, by way of illustration some typical basement waterproofing solutions are shown below: Example 1 - Externally-Applied Basement Waterproofing (Dual Layer)
Oldroyd Xs waterproofing membrane provides waterproofing below the slab.
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Example 2 - Internally-Applied Basement Waterproofing
The basement waterproofing system shown in the diagram on the right is the Oldroyd Xv cavity drainage system. This waterproofing system consists of a dimpled plastic membrane (Oldroyd Xv) which is fixed to the walls and floors of the basement. This forms a "drained cavity" which redirects any water entering the basement into an Aquadrain perimeter drainage channel (shown in green on the diagram). The Aquadrain drainage channel leads to a sump and pump that removes the water from the basement. Alternatively, a cementitious "tanking" system such as Vandex BB75 can be used. This is applied to the internal walls of the basement by trowel or spray. Rather than redirecting the water, it forms a physical barrier - preventing any dampness from entering the basement. For this reason a sump and pump are not required. For further information on internally-applied basement waterproofing systems, see our cellar conversions page. |
Example 3 - Waterproofing Diaphragm and Piled Walls
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Basement Waterproofing CPD Seminars (RIBA Approved)
References1) Basement Information Centre . Approved Document - Basements for Dwellings . TBIC, Blackwater, 2004. 87pp. TBIC/001. |
©Safeguard Europe Ltd. All rights reserved. Registered in England and Wales. Company Number 1721203. |
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Basements are enjoying a resurgence, particularly in residential developments where their benefits had traditionally been overlooked in the UK. 
Waterproofing the external walls of the basement has the benefit of preventing water and contaminants from entering the fabric of the building. The diagram on the left shows a "dual layer" basement waterproofing system. Vandex BB75E elasticised waterproofing slurry forms the primary waterproofing system and is applied directly onto the basement wall by trowel or spray. In this example a closed-cell insulation board is then applied to the wall before the application of the secondary drainage / protection layer (Oldroyd Gtx geocomposite drainage membrane). This secondary drainage layer lessens the stress put on the primary waterproofing system, reducing water ingress caused by possible imperfections in the application of the primary waterproofing system and/or structural movement.
Internally-applied basement waterproofing systems are most commonly used on basement conversion projects. However, they are also utilised on newbuild basement projects where it is difficult to apply a waterproofing system externally - e.g. due to the proximity of neighbouring buildings. 
Diaphragm walls and contiguous/secant piled walls are commonly used in the construction of large commercial basements. Because of the way these types of wall are constructed, it is only possible to position the waterproofing on the internal face of the wall. Waterproofing solutions for these types of wall are therefore similar to those used to waterproof internal basement walls (see above) although they are adapted to take account of the higher levels of water ingress that might be expected in larger basements - e.g. the cavity drainage waterproofing system shown in the diagram on the left uses the large-stud-size Oldroyd Xv20 drainage membrane to provide a larger drainage cavity than would be the case with standard drainage membranes. 
An alternative approach to waterproofing contiguous and secant piled basement walls is to sandwich a layer of Vandex Super crystalline active waterproofing slurry between a layer of shotcrete and a layer of insitu concrete (see diagram). 
Safeguard offer two RIBA-Approved CPD Seminars free-of-charge to architects and specifiers on the UK mainland entitled,"Waterproofing Existing Basements" and "Waterproofing Basements and Underground Structures (Newbuild)." To arrange a seminar call 01403 210204 or use the