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basement drainage |
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Basement Drainage
| Basement Drainage: BS 8102 1990 states that ‘almost all basement structures are likely to be subjected to water pressure at some period of their life’. This assumption of hydrostatic pressure dictates that some form of water removal system should be fitted with in below ground structures. Water entering the building through the walls is controlled behind the membrane and can be directed to a drainage channel at the base of the wall, allowing relief of any build-up of hydrostatic pressure at the vulnerable wall/floor junction. Water enters the channel through a series of drainage ports and is diverted to a natural drainage outlet point or to a suitable mechanical pump & sump arrangement. Various Mechanical Sump and Pump kits have been specifically designed for the purpose of controlling ground water ingress without risk of back-up or flooding in basement refurbishment projects. |
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A 130mm deep x 130mm wide trough is formed in the floor at the wall/floor junction. The dimpled cavity drain membrane stops at least 100mm below existing floor level & 20-30mm short of the base of the trough.
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A shallow bed of 20mm stone is laid along the base of the trough and a perforated channel is laid onto stone with its up-stand flat against the waterproofing/membrane. Channels are butt-jointed on straight runs and mitred at corners. Channel joints should are sealed. |
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A chase is made in the floor where the channel is to be fed into a sump. The channel outlet section is fitted at the appropriate location and the remaining gap between the channel and the side of the trough is filled with 20mm stone to finish flush with the flat top face of the channel. |
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The trough is raised to floor level using: a) 20mm stone if a fully sealed basement conversion system or b) Sand/cement screed (approx 50mm) no membrane is used on the floor. |
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The channel outlet section is connected to a natural drain or is fed into a sunken sump that is serviced by a submersible mechanical pump arrangement. Water is collected in the sump and is pumped out of the building silently and effectively. |
As warm air rises, basements are typically cooler than the rest of the house and therefore have a lower dew-point. To minimise risk of condensation it is vital to ensure new basements are well heated and ventilated, particularly on occasions of high humidity.
For free assistance in matters relating to basement lining systems in domestic housing phone the Twistfix technical help and advice line on 0845 123 6006 or visit www.twistfix.co.uk |