Waterproofing is one of the most expensive defect categories in residential building, and almost every failure is invisible until it is a stain on the ceiling below or tiles lifting a year after handover. By then the fix is a strip-out. The pre-cover inspection is the only moment the membrane can be checked at all. This checklist covers it for bathrooms, laundries and balconies.
The standards behind the checklist
For internal wet areas, the National Construction Code references AS 3740 Waterproofing of domestic wet areas. It sets where waterproofing is required in each zone of a wet area, how far membranes run up walls, what happens at junctions and penetrations, and the falls that stop water ponding. External balconies and decks fall under separate external waterproofing requirements, and every membrane system has its own manufacturer’s instructions for substrate, primer, thickness and curing. The checklist states no heights or overlaps: check those against the current standard and the system you are using. Our AS 3740 guide explains what the standard covers in plain terms.
Where failures actually start
The flat field of a membrane rarely fails. The junctions and the substrate do. A wall-floor junction without a bond breaker cracks as the building moves. A puddle flange not lapped into the membrane lets water bypass it. A door threshold without a water stop leaks into the hallway. A membrane rolled onto damp or dusty screed never bonds. That is why section 4, junctions and penetrations, is the longest part of the checklist, and why section 2 starts with the substrate.
Falls: the cheapest test there is
Water that does not drain eventually finds a way through. Check the floor falls to the waste with no ponding before the membrane goes on, and again after. On balconies, falls must run away from the building to outlets, with an overflow so a blocked outlet does not flood the room inside. A bucket of water and a few minutes will show you what a spirit level misses.
Flood testing
Where it is specified, or where there is any doubt, flood test the membrane before tiling: plug the waste, fill the area to a set depth, and check below for leaks during and after the test. It costs a day. A leak found after tiling costs the whole room.
Who is responsible
The waterproofer warrants their work, and in NSW waterproofing is licensed work, so check the licence before engaging them. But under most residential building contracts, the builder is responsible to the owner for defects in the work, whoever did it. When a waterproofing defect appears during the statutory warranty period, the builder’s own pre-cover inspection, with dated photos of every junction and the waterproofer’s certificate, is what shapes the outcome. Our guide to balcony and wet-area waterproofing defects covers the cost and claim patterns.
Mandatory inspections
The NSW principal certifier’s mandatory critical stage inspections include waterproofing of wet areas before it is covered for certain building classes. Check your certifier’s inspection schedule for the job and book it before the tiler, not after.
Protect it after inspection
A membrane passed on Monday can be damaged by Tuesday: a dropped tool, a wheelbarrow, a tiler’s trowel scraping the upturn. The sign-off asks for the tiler to be told the membrane must not be damaged, and any damage repaired and re-inspected before it is covered. Record the inspection in the inspection and test plan as a hold point that the tiling cannot pass without.
Balconies: the details that fail
Balconies over living spaces are among the highest-risk waterproofing details in residential construction, because they are exposed to weather, often have shallow falls, and sit over rooms where a leak does the most damage. The checks that matter most:
- Threshold: the step-down or threshold detail at the door, and the membrane turned up behind the sill as the system details it.
- Falls and outlets: falls away from the building to outlets, with an overflow so a blocked outlet does not flood inside.
- Upturns: membrane carried up walls and behind cladding, with flashings lapped correctly over it.
- Balustrade fixings: posts and brackets that penetrate the membrane sealed as the system requires, or fixed through the face instead of the floor.
Our guide to balcony waterproofing defects covers why these fail and what the repairs cost.
Renovation bathrooms
Bathroom renovations bring waterproofing risks that new builds do not: existing substrates of unknown condition, timber floors that move more than slabs, old wastes at the wrong height, and junctions with existing walls. Strip back to a sound substrate, fix or replace flooring so it is stable, set wastes and falls correctly rather than working around the old ones, and follow the membrane system’s requirements for timber substrates. Renovation work is where shortcuts are most tempting and where the same inspection matters most.
