Guides · Western Australia

Waterproofing defects: AS 3740:2021 explained for homeowners

Failed waterproofing is one of the most common and most expensive defects in new homes, because by the time you see it, the damage is usually behind the tiles.

General information, not legal advice — check current requirements with the Building and Energy / Building Commission or a lawyer.

Which rules apply to a bathroom in a house

For houses, the wet-area rules come from the National Construction Code (NCC). In NCC 2022 Volume Two, clause H4D2 says that compliance with AS 3740 or with Part 10.2 of the ABCB Housing Provisions satisfies the performance requirement for wet areas, provided the wet areas are protected in line with clauses 10.2.1 to 10.2.6 and 10.2.12 of the Housing Provisions.

AS 3740 is the Australian Standard “Waterproofing of domestic wet areas”. The current edition is AS 3740:2021; it replaced AS 3740-2010, and NCC 2022 references the 2021 edition. We do not reproduce the standard’s text here — Australian Standards are copyright and sold separately. The Housing Provisions, by contrast, are free to read.

Which edition applies to your home? Generally the edition in force for your building approval. NCC 2025 has since been published and is being adopted by the states on their own timetables, so check which NCC edition applied to your permit before relying on any clause number on this page.

What the Housing Provisions require in a shower

Part 10.2 of the ABCB Housing Provisions 2022 says building elements in wet areas must be protected with a waterproofing system (clause 10.2.1). For a shower with a hob, step-down or level threshold, clause 10.2.2 requires:

  • The floor of the shower area to be waterproof, including any hob or step-down.
  • The walls to be waterproof not less than 1800 mm above the floor substrate.
  • Wall junctions and joints within the shower area to be waterproof not less than 40 mm either side of the junction.
  • Wall/floor junctions and penetrations (such as tap and mixer holes) within the shower area to be waterproof.

Where there is a floor waste, clause 10.2.12 requires the floor to fall to it at a minimum of 1:80 and a maximum of 1:50. Water sitting in a shower or on a bathroom floor is often the first visible sign that falls are wrong.

What the WA tolerances guide says

The Western Australia Guide to Standards and Tolerances 2019 is an advisory guide, not a regulated standard, but it is commonly used in WA disputes. It says waterproofing of wet areas is defective if not installed in accordance with the Building Code of Australia and AS 3740 (clause 14.02), and that shower recesses and components are defective if they crack, leak or do not perform as intended (clause 14.03).

It is also fair to the builder in places, and you should be too: it treats replacing silicone after about five years as normal owner maintenance, water beading on some surfaces as normal, and says unenclosed shower screens are not intended to stop water spreading.

Signs worth recording

  • Damp or stained skirting, plaster or carpet on the other side of a shower wall or in the next room.
  • Swelling vanity or cabinet panels near the shower or bath.
  • Loose, drummy or cracked tiles and failing grout in or around the shower (see our tiling guide).
  • Water ponding on the shower floor or flowing away from the waste.
  • Mould or a persistent musty smell that returns after cleaning.

What to do next

  1. 1Stop the damage spreading. If you can, avoid using the affected shower until it is assessed, and photograph anything you do to make it safe.
  2. 2Document it properly. Wide, mid and close-up photos, dated, with the item numbered. Note when you first saw it.
  3. 3Tell the builder in writing. Describe the symptoms, not a diagnosis — “damp skirting in hallway behind ensuite shower, see photos” — and ask them to investigate.
  4. 4Get the cause assessed by someone qualified. Waterproofing failures are hidden behind finishes. Building and Energy inspects issues in most WA complaints, but you may also want a private inspector or a moisture assessment.

See how to document defects, tiling defects and drummy tiles, and the standards library.

Frequently asked questions

What is AS 3740?

AS 3740 is the Australian Standard “Waterproofing of domestic wet areas”. The current edition is AS 3740:2021, which replaced the 2010 edition. For houses, the National Construction Code accepts compliance with either AS 3740 or Part 10.2 of the ABCB Housing Provisions for wet areas.

How high must shower walls be waterproofed?

Under Part 10.2 of the ABCB Housing Provisions 2022 (clause 10.2.2), shower walls must be waterproof to not less than 1800 mm above the floor substrate. That 1800 mm figure was a change made in NCC 2022, so a home approved under an earlier edition may have been built to a different requirement.

Is a leaking shower always a defect?

The WA Guide to Standards and Tolerances 2019 says shower recesses and components are defective if they crack, leak or do not perform as intended, and that a component is defective if it lets the shower recess leak in normal use. It also treats replacing silicone after about five years as normal owner maintenance.

Can I read AS 3740 for free?

Australian Standards are generally sold, not free. The ABCB Housing Provisions, which includes the wet-area rules in Part 10.2, is free to read from the ABCB website.

Keep your defect record in one place

Defend My Build keeps each defect’s photos, location and notes together in one project, and lays the list out as a Scott Schedule you can export to CSV. There is a free plan.

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Sources checked for this page

Last reviewed 2026-10-13. Requirements change — check the current version of each source.

Related guides

General information, not legal advice — check current requirements with the Building and Energy / Building Commission or a lawyer.