STRUCTURAL ELEMENTS Hidden benefits
Using basements to maximise space without expanding a building’s footprint is increasingly popular, but keeping groundwater out can be difficult, and remediation costly. James Berry of the Property Care Association looks at the options
poor workmanship, the inappropriate use of materials, or simple bad design. As a result, a range of factors need to be carefully considered when undertaking such works, to ensure a positive outcome. Architects often approach our organisation – the Property Care Association (PCA), which represents the UK’s structural waterproofing sector – for advice. There are some key considerations when designing a water-tight basement, as follows.
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First steps It’s important to get help right from the start. Ideally, a design team will include a geotechnical specialist and a waterproofing specialist, and I would advise that both are engaged at the earliest possible stage. These specialists can give key advice on the ground conditions and in assessing the site. It’s important that the geology, hydrogeology, and topography as well as the external drainage options and groundwater conditions of a site, are carefully considered. The type of soil and the water table also need to be evaluated, as well as any ground gas concerns. There are a number of resources available to architects. BS 8102:2009 Code of Practice for Below Ground Structures Against Water from the Ground is considered the ‘waterproofer’s bible.’ Other useful documents include the Construction Industry Research and Information Association 139 and 140 Water Resisting Basements, as well as the PCA Code of Practice for Waterproofing of Existing Below Ground Structures.
Waterproofing options Understanding the target grade of the environment is key to choosing a suitable waterproofing system. BS 8102: 2009 details three grades, each providing a
ADF JULY 2021
lthough hidden away, structural waterproofing can be particularly sensitive to failures, largely due to
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different level of dryness. Examples of a grade 1 structure include a car park and plant room without electrical equipment, where it’s considered tolerable to have some seepage and damp areas. No water penetration is acceptable for grade 2 structures, and for damp areas that are tolerable, ventilation might be required. Similarly, grade 3 accepts no water penetration, but this performance level also specifies ventilation, dehumidification or air conditioning as necessary and appropriate to the intended use.
The target grade and site conditions inform which of the resulting three waterproofing systems, (Type A, B or C) is most suitable. In some cases, a combination of systems will be appropriate. Type A, usually referred to as ‘barrier protection,’ is a structure with no integral protection against water penetration.
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Understanding the target dryness grade of the environment is key to choosing a suitable waterproofing system
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