What waterproofing do bathrooms and other wet areas need, and who checks it?

Bathrooms, laundries, toilets, showers and balconies need a waterproofing membrane applied to the floors and walls in the areas set out by the National Construction Code, usually to Australian Standard AS 3740 for internal wet areas. Leaks behind tiles are a common and expensive defect, so the membrane must go down before tiling and be allowed to cure. In some states the waterproofer must hold a licence. The installer usually provides a waterproofing certificate, and your certifier may inspect the membrane or ask for the certificate before final sign off. Ask your certifier what they need before the tiler starts.

General information only. Requirements vary by state or territory and change over time, so check the current rules for your location.