Shea CullenNSW Registered Architect 9748 · Updated 17 July 2026Waterproofing is one of a handful of things in a build that gets covered up and then has to keep working for years underneath tiles, screed and fixtures. Once it is buried, finding a failure means demolishing the room in front of it, so the cheap moment to get it right is before it is covered, not after.
This checklist is what to confirm while you still can. It matters most on a house you are building yourself, where you, not the builder, are the person the law holds responsible for the critical stage inspections. Work through it before the tiler arrives.
Waterproofing in a wet area is one of six mandatory critical stage inspections for a house in NSW, under clause 61(2)(d) of the Environmental Planning and Assessment (Development Certification and Fire Safety) Regulation 2021. Almost every owner assumes the builder is responsible for making those inspections happen. Clause 61(1) says otherwise: the duty to ensure the work is inspected sits on the person with the benefit of the development consent, which on a normal house build is you. The maximum penalty for an individual is 150 penalty units. At the current rate that is roughly $16,500. You do not carry out the inspection yourself and you have no statutory right to attend it, but you are the person the law holds responsible for it happening. Ring your principal certifier yourself and confirm the date. Do not rely on being told.
This is the killer item on this list and the cheapest thing you will ever do. Once the tiles are on, the membrane is gone from view for the life of the building, and every future argument about it becomes your word against theirs. Walk each wet area with your phone. Wide shot of the whole floor, then close ups of every corner, every junction where floor meets wall, every pipe and tap penetration, every waste, and the full height of the membrane up each wall. Get the date on the photos. If a dispute ever starts, this folder is the difference between a claim and a feeling. Owners who skip this step are not being lazy, they simply do not realise that this is the last day the evidence exists.
Do not assess falls by eye and do not accept a reassurance. Get a bottle of water and pour it on the floor of every wet area before the membrane is covered. It should run to the waste and leave nothing behind. If water sits anywhere, it will sit there for the next forty years, and ponding is what turns a small detailing fault into a leak. Fixing a fall now costs a screed. Fixing it after tiling means demolishing the room. This is the single most common thing I see people wish they had checked, because it is obvious the moment you test it and invisible the moment you do not.
The bathroom floor should be set down in the slab or the floor structure far enough that once the screed, membrane and tile are on, the finished surface sits level with the room next door. Not a step up. This matters for three reasons: if the bathroom ever overflows you want the water contained rather than running into carpet, a level threshold is far more usable as you age, and a robot vacuum can cross it. It is worth checking now because the setdown was decided at the pour. If it was missed, the only remaining fixes are a step, a ramp, or a hob, and none of them are what you wanted.
The field of a membrane almost never fails. The failures cluster at the details: terminations, junctions, pipe and tap penetrations, wastes, thresholds. Every place something passes through the membrane is a place water can get behind it. Walk the room and count them, then check each one has been properly treated rather than simply painted over. Ask your waterproofer to talk you through each penetration. A good one will be pleased you asked. This is also why membrane brand matters less than people think. A quality membrane badly detailed will fail long before a modest one detailed properly.
Membranes have a manufacturer's specified curing time before anything can be laid over them, and it is one of the first things sacrificed when a job is running late. A membrane tiled over too early can be compromised before the room is even finished, and nobody will ever know, because it is under the tiles. Ask what product was used, ask what the manufacturer requires, and ask when it went down. The dates should work. If they do not, say so now, because this is a conversation that is impossible to have later.
The membrane can pass its inspection and still be ruined the following week, by someone screwing a shower screen into the hob, fixing a vanity through the floor, or dropping a tool on it. Once the waterproofer leaves, nobody feels responsible for it. Make it explicit with your builder that nothing gets fixed through a waterproofed surface without the waterproofer being told, and that any penetration made after sign off gets made good and photographed. This costs nothing to say now.
Where a habitable room sits against a retaining wall, such as a garage or a room dug into a slope, do not accept a single tanking membrane as the only thing between you and the ground. Build it as two walls with an integral concrete hob and drainage in the cavity between them. The reason is access. A membrane has a working life of roughly ten to fifteen years and the room in front of it is meant to last a great deal longer, so sooner or later that membrane will need attention. A membrane buried against earth is one you cannot inspect, cannot maintain and cannot repair without demolishing the room in front of it. Anything you cannot inspect, you should design so that its failure is survivable. The cavity and the hob are what make a failure a drainage problem instead of a demolition.
If there are retaining walls, specify aggregate for at least 300mm behind the wall, all the way to the top, with a drainage pipe underneath it. Two things go wrong without it. Water builds up behind the wall with nowhere to go and finds the membrane instead, and if there is clay sitting against the wall it expands and contracts with every wet and dry season until the wall cracks. Once it is backfilled you cannot see any of this, and putting it right means excavating the whole wall again. This is a check that takes ten minutes on the day and saves a five figure repair.
Look at the driveway, the paths, the patio and the thresholds. Every one should fall away from the building. A driveway that slopes towards the house is a channel pointed at your front door, and no amount of waterproofing at the threshold fixes a drainage problem upstream of it. This is much easier to see now, while levels can still be adjusted, than after the concrete is down. If your site slopes towards the house, this is the item on this list most likely to cost you money.
Waterproofing is a major element, so the statutory warranty under section 18E of the Home Building Act 1989 runs six years from completion. Non major defects run two. That six years is far shorter than the life you are expecting from the building, and it is the real reason this checklist exists. Detailing and installation failures show up in the first few years, which is inside the window, but only if you notice them and act. Watch for drummy tiles, staining at ceilings or slab edges, efflorescence, and a musty smell that does not go away. Those are the early symptoms. Investigate them when they appear rather than sealing over them.
This is one of six moments in a NSW house build where work is about to be covered permanently. The waterproofing one matters most because waterproofing is the single largest defect category in NSW residential buildings. In the Building Commission's 2025 strata research, 53 percent of buildings had serious defects in common property, and waterproofing was the most common at 44 percent.
If you want the honest version of how long a membrane actually lasts, I have written it up in waterproofing membrane lifespan in Australia, including why the figure everyone quotes has no source behind it. If something is already leaking, the balcony guide covers the sequence to follow, and who pays for waterproofing defects in strata covers the responsibility question.
One thing this checklist deliberately does not do is tell you whether what you are looking at is serious. It licenses you to notice, not to conclude. If you spot something on this list and you are not sure how much it matters, that is exactly the question worth an hour of an architect's time before the tiles go on rather than after.