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Ground Stability, Foundations and Substructures 153
If the water flow is expected to be relatively high, a sealed cavity system is used. All of
the water that penetrates the wall flows, under gravity, to a sump pit where it is then
pumped away. In existing buildings, where the walls of a basement are damp and not
subject to water flow, a ventilated cavity system may be used. The cavity helps to keep the
damp surface away from the internal wall and wall finishes. Moisture on the internal face
of the wall will evaporate and the ventilation system guides the moist air out of the structure
(Photograph 3.16a and b shows a ventilated and sealed drain cavity applied to a wall).
(a)
(b)
Photograph 3.16 (a) Polypropylene ventilated cavity drain sheet applied to brick wall to
control damp. (b) Sealed cavity drain allows water to flow to sump where it is pumped
away.