Shower & Wet Area Waterproofing (NCC 2025)

The requirement

Inside the shower, the walls must be waterproof up to at least 1800 mm above the floor. So must the shower floor, the junctions and any penetrations. Walls within 75 mm of a bath, basin or sink must be water-resistant to at least 150 mm above the fixture (NCC 2025, clause 10.2).

Water is the thing that wrecks a bathroom. So the rule book, the National Construction Code (NCC), says which parts of a wet area you have to seal, and how well. There are two levels of sealing:

• Waterproof means a full barrier that water cannot get through. That is your membrane.
• Water-resistant means the surface stands up to water. It is not a sealed barrier.

The NCC asks for waterproof in the wettest spots. Water-resistant covers the splash zones. Here is where each one goes.

Inside the shower (clause 10.2.2). This is the wettest part of the house. Nearly all of it must be waterproof.

The 1800 mm wall height is set by the NCC itself, not by any standard. That is the number to build to inside the shower.

1. 1 shower floor
2. 2 basin / bath

Outside the shower (clauses 10.2.3 and 10.2.5). Out here the rules ease off. They also change with what you are building on.

• Floors only need to be water-resistant on a concrete or fibre-cement substrate. On a timber-based substrate, like particleboard or plywood, the floor must be fully waterproof. The material under your feet decides it.
• Walls within 75 mm of a bath, basin or sink must be water-resistant to at least 150 mm above the fixture. That is the splash zone.

There is no single wall height for the whole room. It depends on what the wall sits next to. Build to 1800 mm inside the shower. Build to 150 mm above a bath or basin. A dry wall needs nothing extra.

AS 3740 is optional. The NCC (clause 10.2.1) lets you follow AS 3740, the wet-areas standard, as one way to get the job right. But it is not compulsory. You can instead follow the NCC’s own wet-area clauses (10.2.7 to 10.2.32). If you take the AS 3740 path, follow it and the membrane maker’s instructions.

On site — what to waterproof

A quick run-through before you start rolling membrane:

1. Shower floor. Waterproof the whole floor. Don’t forget the hob or step-down.
2. Shower walls. Waterproof up to at least 1800 mm off the floor.
3. Junctions. Waterproof every wall junction, at least 40 mm each side. Do every wall-to-floor junction too.
4. Penetrations. Seal around the waste, taps and mixer.
5. The floor outside the shower. Waterproof it over a timber-based substrate. Water-resistant is enough over concrete or fibre-cement.
6. Walls beside a bath, basin or sink. Go water-resistant to at least 150 mm above the fixture, wherever the wall sits within 75 mm of it.
7. Membrane. Follow the maker’s instructions, and AS 3740 if you are on that path. The product’s own specs come from the maker, not the code. That covers coats, cure time and primer.

Related

• Part of the NCC rules for Australian chippies. That is the pillar page, with the state-by-state adoption tracker.
• Building the room around it? See NCC minimum ceiling heights. It covers the 2.1 m rule for bathrooms and laundries.
• Setting out the wet-area floor falls and drainage is a plumbing job. Check with your plumber and the relevant plumbing standard.

Sources

• NCC 2025, ABCB Housing Provisions Standard, Part 10.2 “Wet area waterproofing” (clauses 10.2.1–10.2.32) — what must be waterproof vs water-resistant, the 1800 mm shower-wall height, the 40 mm junction rule, the 150 mm/75 mm rule at baths and basins, and the timber-vs-concrete floor split. Confirm at ncc.abcb.gov.au. (Confirmed against the NCC 2025 Housing Provisions Standard, verified 2026-07-28.)
• AS 3740 “Waterproofing of domestic wet areas” — an optional compliance path offered by NCC clause 10.2.1. It is paywalled; check the membrane and detail figures there (and your membrane maker’s instructions) if you use that path — do not treat any AS 3740 figure as a code minimum.