Ground Moisture

Ground moisture can infiltrate living spaces by way of the floor or directly to the ceiling space by way of vented cavities. The cavity should be constructed to prevent the migration of water vapour into the ceiling space. Wet subfloors can be isolated by laying polythene tightly over the surface and taping all joints.  More information can be obtained from the Good Repair Guide: Damp Subfloors (BRANZ).

Concrete floors must be installed over a damp-proof membrane (DPM) to ensure that moisture from within the ground does not penetrate the slab. This membrane can be formed by a polyethene sheet that is taped at the laps and laid over compacted hard fill topped by a sand blinding layer. The DPM must be installed under the full extent of the slab, under any internal or perimeter foundations, extend up to the external edge of the floor slab, and lapped and sealed under the wall damp-proofing system.


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