Rooms below ground level are subject to lateral dampness as walls and floors are soil retaining, calling for specialist waterproofing techniques.

Cavity drainage membrane is a high density studded plastic membrane for lining walls, floors and ceilings, allowing water to be channelled into a draining system and pumped outside. The membrane can be wet plastered or dry lined with plasterboard and skim finished, and floors can have a cement screed applied or be timber boarded.