Waterproofing

Waterproofing is the general name for the measures that stop water passing into the structure and the interior wherever a building is exposed to it. Foundations and basement walls are protected from groundwater, roofs and terraces from rain, and bathrooms, kitchens and other wet rooms from water in daily use. A large share of the complaints people have about buildings trace back to waterproofing that was missing or done badly.

Types and critical points

The most common materials are bituminous membranes, synthetic membranes, liquid-applied systems and cementitious coatings. In basements, wrapping the whole structure from the outside is known as tanking. The real risk is rarely on flat surfaces; it lies at junctions: wall-to-floor corners, pipe penetrations, drains, parapets and door thresholds. Membranes must be turned up vertical surfaces far enough, corners reinforced with fillets or tape, and laps respected. The protection layer laid over the membrane matters just as much, because a membrane punctured during backfilling or tiling no longer works. The order of waterproofing and thermal insulation, and how vapour moves through the build-up, are designed together in the detail.

Waterproofing in the project

Waterproofing rarely shows up in a render, but it always appears in construction details and sections. A good set of construction documents spells out the layer sequence and edge details for every wet room and roof.