Cut-away scale model of a bathroom showing substrate, a blue waterproof membrane lapped up the walls, bond breaker at the wall and floor junction, and a shower floor falling to a waste.

AS 3740 explained: the Australian waterproofing standard for domestic wet areas

In short

  • AS 3740 is the Australian Standard for waterproofing domestic wet areas: bathrooms, showers, laundries, toilets and the like. The current edition is AS 3740:2021.
  • Both NCC 2022 and NCC 2025 reference AS 3740:2021, so the edition does not change when your state moves to NCC 2025.
  • For apartments (Class 2), Class 3 buildings and Class 4 parts, NCC Volume One requires wet areas to comply with AS 3740. Bathrooms, laundries and sanitary compartments in Class 5 to 9 buildings must comply as if they were in a Class 2 or 3 building.
  • For houses (Class 1), you have two Deemed-to-Satisfy routes: AS 3740, or the wet area provisions in Part 10.2 of the ABCB Housing Provisions.
  • External waterproofing (balconies, podiums, roof decks, planters) sits under AS 4654, not AS 3740.

Correct as at September 2026.

Wet area leaks rarely announce themselves. The tiles look fine, the grout looks fine, and the first sign of trouble is a stain on the ceiling below or a swollen skirting next door. By then, the question is not what went wrong. It is who pays.

For most wet areas in Australia, the answer starts with AS 3740. Here is what it covers, how it links to the NCC, and where designers carry the risk.

Which edition applies

The current edition is AS 3740:2021 Waterproofing of domestic wet areas, published on 23 July 2021. It superseded AS 3740:2010 and its 2012 amendment. Standards Australia lists the 2021 edition as current.

NCC 2022 and NCC 2025 both list AS 3740:2021 as a referenced document. If your details, specification clauses or product data sheets still cite AS 3740:2010, update them now. The edition will not change when your state moves to NCC 2025.

Which buildings it covers

Standards Australia describes AS 3740:2021 as setting minimum requirements for the materials, design and installation of waterproofing for domestic wet areas in Class 1, Class 2 and Class 4 buildings. It also applies to wet areas in Class 3 to 9 buildings as if they were a Class 2 or Class 4 part of a building.

The NCC is where that becomes mandatory. In NCC Volume One, clause F2D2 says building elements in wet areas in a Class 2 or 3 building or a Class 4 part of a building must be water resistant or waterproof in accordance with Specification 26, and comply with AS 3740. In a Class 5, 6, 7, 8 or 9 building, the same applies to bathrooms, shower rooms, slop hopper or sink compartments, laundries and sanitary compartments, as if they were in a Class 2 or 3 building.

So a shower in an office end-of-trip facility or a childcare centre bathroom is still AS 3740 territory. It is not only a residential Standard.

Houses have two routes

For Class 1 and 10 buildings, NCC Volume Two points to both AS 3740 and Part 10.2 of the ABCB Housing Provisions. Wet area elements must be waterproof or water resistant as set out in Housing Provisions 10.2.1 to 10.2.6. The construction can then follow either:

  • AS 3740, together with the floor fall rule in Housing Provisions 10.2.12; or
  • the Housing Provisions construction clauses, 10.2.7 to 10.2.32.

Part 10.2 is free to read on NCC online. A few of its requirements worth knowing by heart:

  • Showers. The shower floor, including any hob or step-down, must be waterproof. Shower walls must be waterproof to at least 1800 mm above the floor substrate, and wall junctions, wall/floor junctions and penetrations in the shower area must be waterproof.
  • Outside the shower. Concrete and fibre-cement floors must be water resistant. Timber floors, including particleboard and plywood, must be waterproof. Wall/floor junctions must be waterproof.
  • Falls. Where a floor waste is installed, the floor must fall to it at no less than 1:80 and no more than 1:50.
  • Materials. Membranes complying with AS/NZS 4858 are one of the materials deemed waterproof.
Check the accessible bathroom. Where the ABCB Livable Housing Design Standard applies to a new home, the NCC notes that shower hobs and similar details can only be used in bathrooms that are not subject to it. Adoption of the livable housing provisions varies by state, so confirm the position for your site before you draw a hob.

What the Standard deals with

AS 3740 works through the same questions every wet area raises: which surfaces must be waterproof and which only water resistant, how far treatment extends around each fixture, what the membrane can be applied to, how floors drain, and how junctions and penetrations are treated.

For a designer, the practical checklist is:

  • Extent of treatment around showers, baths, basins, tubs and floor wastes.
  • Falls that drain to the waste without ponding.
  • Substrate suitability and preparation. A membrane over a substrate that flexes, moves differently from its neighbour or will not bond can fail no matter how good the product is.
  • Junctions at wall to floor, wall to wall and changes of substrate. Movement concentrates here, and this is where leaks often start.
  • Penetrations for taps, spouts, pipes and floor wastes.

Where it goes wrong

The failures that turn up in defect disputes are rarely exotic. They are junctions detailed loosely, membranes applied over poorly prepared substrates, membranes applied too thin, tiling before the membrane has cured, and falls that send water the wrong way. Movement at the wall to floor junction of framed construction is a common culprit as a building settles and moves with the seasons.

Who does what, and what to keep

The designer specifies the system and produces documentation that supports compliant installation. The builder makes sure the substrate is ready and the waterproofing happens at the right stage. The waterproofer installs to AS 3740 or the Housing Provisions and the manufacturer’s instructions.

Licensing depends on the state. In NSW, waterproofing is trade work, and a contractor licence is needed for residential work valued at more than $5,000 including labour, materials and GST. In Queensland, a QBCC licence is generally needed for building work valued over $3,300, and waterproofing is its own licence class. Other states set their own rules, so check with your regulator rather than assuming.

Whether a formal waterproofing certificate is legally required also varies by state and by certifier. Either way, ask for written confirmation from the installer of the system used and the Standard it was installed to. Photos of substrate preparation, junction treatment, membrane application and cure times are the most useful evidence you can hold if a claim arrives years later, and they cost almost nothing to take.

External waterproofing is AS 4654

Balconies, podiums, planters and roof decks fall under AS 4654.1 and AS 4654.2 (both 2012 editions, referenced in NCC 2022 and NCC 2025). Standards Australia lists both as pending revision. Keep wet area and external waterproofing separate in your specification.

NCC 2025 tightens the rules for external areas in Volume One. Clause F1D4 now requires a concrete roof, balcony, podium or similar part of a building to have a structural substrate graded at no less than 1:80, a step down of at least 70 mm from the internal floor substrate where applicable, and a monolithic hob at least 70 mm high at the outer perimeter unless the perimeter drains directly to a gutter.

When that applies depends on your state. NCC 2025 took effect in Victoria on 1 May 2026, is optional alongside NCC 2022 in the ACT and WA until 1 May 2027, and is due in NSW, Queensland, SA and Tasmania on 1 May 2027. The NT has not adopted it. For the detail and the variations, read NCC 2025 vs NCC 2022: what changed, and when it applies in your state.

Your next steps

  1. Search your standard details and specification for “AS 3740:2010” and update the references.
  2. For houses, decide whether you are documenting to AS 3740 or Housing Provisions Part 10.2, and say so on the drawings.
  3. Detail the junctions, falls and penetrations, not just the membrane.
  4. Ask for installer documentation and photos as a condition of the contract, not as a favour.

CPD on waterproofing

These live courses run one hour each and cover wet area and external waterproofing in practice:

To see how these fit your annual obligations, read the CPD requirements guide and the CPD deadlines calendar.

Frequently asked questions

What is the current edition of AS 3740?

AS 3740:2021 Waterproofing of domestic wet areas, published in July 2021. It replaced AS 3740:2010 and is the edition referenced in both NCC 2022 and NCC 2025.

Does AS 3740 apply to apartments and commercial buildings?

Yes. NCC Volume One requires wet areas in Class 2 and 3 buildings and Class 4 parts of buildings to comply with AS 3740. Bathrooms, shower rooms, laundries and sanitary compartments in Class 5 to 9 buildings must comply as if they were in a Class 2 or 3 building.

Do I have to use AS 3740 for a house?

No. For Class 1 buildings you can follow AS 3740 together with the floor fall rule in Housing Provisions 10.2.12, or follow the construction clauses in Part 10.2 of the ABCB Housing Provisions. Either way, wet area elements must be waterproof or water resistant as set out in Housing Provisions 10.2.1 to 10.2.6.

Does AS 3740 cover balconies?

No. Balconies, podiums, planters and roof decks are external waterproofing and fall under AS 4654.1 and AS 4654.2. NCC 2025 also adds substrate fall, step down and hob requirements for concrete balconies and podiums in Volume One clause F1D4.

Do waterproofers need a licence?

It depends on the state. In NSW a contractor licence is needed for residential waterproofing work valued at more than $5,000. In Queensland a QBCC licence is generally needed for building work valued over $3,300. Check the rules with the regulator in your state.

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