Failed waterproofing is one of the most common defects in new Australian homes, and one of the most expensive to fix. Once the tiles are down, you can't see the membrane, and by the time a leak shows up in the skirting or the room next door, the damage is done.
This isn't a DIY guide. In a new home, waterproofing is part of your builder's work and is done by a waterproofing contractor (in Queensland, work over the QBCC licensing threshold must be done by a licensed contractor). What this guide gives you is enough knowledge to check the work at the right stages and ask the right questions.
C13B - Waterproofing Installation Checklist
$59.00 AUD
Last updated 5 Oct 2026 · Revision 1 · Free updates for life
Checklist Type: Minor
Form Factor: Fillable, print-ready PDF (A4, 26 pages)
When to use: During and after waterproofing installation, before tiles or finishes cover it
A 205-point waterproofing installation checklist. Check substrate, preparation, flashings, installation, certification and external areas as the work goes in, before it's covered.
What counts as a wet area
Under the NCC, wet areas are rooms with water-using fixtures and a risk of water on the floor or walls: bathrooms, showers, laundries and toilets. Kitchens aren't classed as wet areas, although the wall behind a sink still needs to be water resistant.
Balconies and external decks are a separate topic, covered by AS 4654, not AS 3740.
The rules: NCC and AS 3740
The National Construction Code (NCC) sets out what has to be waterproof or water resistant, in Part 10.2 of the ABCB Housing Provisions. AS 3740 (Waterproofing of domestic wet areas) is the standard that explains how to do it. Following AS 3740 is the usual way to comply.
There's an important difference between the two terms:
- Waterproof means water can't get through. This is the membrane.
- Water resistant means the material can handle being wet occasionally, like tiles, fibre cement sheeting or concrete.
The Australian Institute of Waterproofing (AIW) has a good visual guide to the AS 3740 requirements:
Key requirements in plain English
Inside the shower
- The floor must be waterproof, including any hob or step-down.
- The walls must be waterproof to at least 1800 mm above the floor substrate.
- Wall corners and joints must be waterproof at least 40 mm either side of the junction.
- The wall-to-floor junction must be waterproof.
- Every penetration (taps, shower arm, waste) must be waterproof.
Outside the shower
- Concrete or fibre cement floors must be water resistant. Timber-based floors (like particleboard upstairs) must be waterproof.
- The wall-to-floor junction must be waterproof, with a flashing that extends at least 40 mm horizontally onto the floor.
- Doorways generally need a waterstop under AS 3740 so water on the floor can't run out under the door into the next room.
Baths, basins and tubs
- Walls within 75 mm of a bath, basin or laundry tub must be water resistant to at least 150 mm above the vessel.
- The wall-to-floor junction along a built-in bath must be waterproof.
- An inserted bath needs a waterproof shelf with a waterstop under the lip.
Laundries and toilets
- Floors and wall-to-floor junctions must be water resistant.
These are the minimums. Many good builders waterproof the whole bathroom floor as standard, which I'd always recommend.
Membrane types
Membranes are rated by how much they can stretch to cope with building movement: Class I (low), Class II (medium) and Class III (high). The designer or installer chooses the class to suit the substrate and the expected movement.
- Liquid-applied membranes. By far the most common in Australian bathrooms. These are polyurethane, acrylic or hybrid products rolled or brushed on. They must be applied to the manufacturer's dry film thickness, usually in two coats at right angles, with bond breakers or reinforcing tape at corners and junctions.
- Sheet membranes. More common on balconies, roofs and in larger commercial areas. Some systems are used in bathrooms, particularly over timber floors.
- Preformed shower bases and trays. Sometimes used instead of a membrane under the shower floor.
Sealants and grout are not membranes. They help, but they're not what keeps water out of the structure.
The stages to check
The time to find a waterproofing problem is before the tiler covers it up. Check these hold points, or have an independent inspector do it:
- Before the membrane. Substrate is clean, sound and dry. Floor falls to the waste are correct. Puddle flanges are fitted at the floor wastes. Fibre cement and wet area plasterboard are fixed to the manufacturer's requirements.
- After the membrane, before tiling. Membrane is continuous with no gaps, pinholes or thin spots. Corners and junctions have bond breakers or reinforcing. Penetrations are sealed. Shower walls are done to the full 1800 mm. Waterstops are in at doorways.
- After tiling. Falls take water to the waste with no ponding. Junctions between walls, floors and fixtures are sealed with a flexible sealant, not grout.
Take photos of the membrane before it's tiled. Waterproofing defects are covered by the Queensland home warranty scheme, but you'll need evidence of what was installed. Ask your builder for the installer's certificate and the product details too.
Our C13A Waterproofing Design checklist covers what to check on the plans, and the C13B Installation checklist (above) covers the on-site checks. More detail in waterproofing done right and what class is your waterproofing system.
Warranties and maintenance
Ask for the waterproofer's certificate and any product or installation warranty. Keep them with your handover documents.
After you move in, keep an eye on the silicone joints at the floor-wall junction and around the shower screen and replace them when they crack or go mouldy. Signs of a leak to watch for include swelling skirting boards, lifting or drummy tiles, mould at the base of walls and staining in the room next door. If you see any of them in the first year, report it to your builder in writing within your 12-month defects period.
