039 BP 1016

BP 10 October 2016

DAMP PROOFING OCTOBER 2016 | BUILDING PRODUCTS 39 down in the Act. If the neighbours disagree with what is proposed, the Act provides a mechanism for resolving disputes. Once all the legislation has been assessed, and the necessary permissions obtained, it is then down to the construction, and the selection of the right materials for the job. Obviously, there is far more construction work with a new-build basement compared with a refurbishment of a cellar – yet that may be an advantage as the area will be designed and built for purpose. However, once the structure has been created, the work is much the same in either situation. Tanking below ground level most commonly involves the application of a layer of cementitious waterproof render system on the walls, linked to a waterproof screed on the floor. Tanking can also be carried out using a sheet membrane, asphalt or other liquid-applied waterproofing material. Hydrostatic pressure – the external water pressure around the basement – is also a critical factor that needs to be considered. It is crucial that the tanking is securely fixed to the substrate, as the pressure from the water table around the basement can be significant. Hydrostatic pressure will force water through tiny gaps very quickly, so great care should be taken at this stage to ensure the waterproofing will meet the demands made of it. Cavity membranes are a suitable alternative to tanking. Membranes with a studded profile can be used to form an inner waterproof structure. The studded side is placed against the wall, creating an area that allows water to flow down to the floor. Here it flows in a drainage channel to a sump, and is then pumped out to a suitable drainage outlet. Rather than preventing damp from entering the structure, it manages the ingress of water. With external tanking, any slight imperfection will result in damp entering the building, and it then becomes a time consuming and costly repair job that will mean extensive excavation work. This method is also the number one choice in refurbishment work, as the amount of construction work needed is greatly reduced compared with the alternatives. The floor must not be forgotten, and a suitable high capacity drainage membrane should be specified. Good examples feature 20mm studs which offer an impressive compressive strength figure of 150kN/m2. Basement construction can be quick, with no more issues to contend with than a loft extension, and the benefits for the future of the occupiers of the property are substantial. The end result is additional living space that is warm, comfortable, free of damp, and – most importantly to the home owner – capable of adding value to the property. The amounts we are talking about are relative – with the executive property in the centre of London able to fetch more in real terms than a ‘semi’ in a remote, rural area. However, it will add value financially, wherever the dwelling might be. Basements really are a viable option to issue of achieving more living space in a house. Chris Burbridge is Managing Director at Delta Membrane Systems


BP 10 October 2016
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