AS 3740-2021: waterproofing of domestic wet areas
AS 3740-2021 is the Australian standard for domestic wet area waterproofing. Key requirements, NCC link, common defects, and who must hold a licence.
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AS 3740-2021 governs the materials, design, and installation of waterproofing for domestic wet areas on every Australian residential build. The NCC calls it up as a deemed-to-satisfy path under H4D2, so a breach of AS 3740 is a breach of the NCC. The standard specifies where membranes go (full shower, partial bath/laundry/WC zones), what substrates they can bond to, and the pre-tile flood test that must pass before tiles go down. The most expensive defect in residential construction: missed waterproofing. Average Queensland bathroom claim under the Home Warranty Scheme ran close to $25,000 in 2024-25 rectification costs, per QBCC (verified 2026-05-07). Waterproofing work must be done by a licensed contractor in NSW, VIC, and QLD. The standard is paywalled; the ABCB Housing Provisions 2022 Part 10.2 covers the same ground and is free.
In plain English
AS 3740:2021 is the joint Standard that sets minimum requirements for waterproofing domestic wet areas: bathrooms, ensuites, laundries, WCs, kitchens, and balconies above habitable rooms in Class 1, 2, and 4 buildings.
The 2021 edition replaced the 2010 edition. Key additions in 2021: more extensive shower wall requirements, expanded substrate and membrane choices, and clearer design provisions for contemporary wet area layouts (larger format tiles, walk-in showers, freestanding baths).
The NCC 2022 Volume Two calls it up under Part H4 Health and amenity. The Performance Requirement H4P1 is that water must be prevented from penetrating behind fittings and linings, or into concealed spaces, in sanitary facilities, bathrooms, laundries and the like (verified 2026-05-07, NCC 2022 H4). Compliance with AS 3740 satisfies H4P1 as a deemed-to-satisfy (DTS) path. So does following Part 10.2 of the ABCB Housing Provisions 2022. Builders and waterproofers can use either, or a mix of both.
What it requires
Waterproofing zones
The zones differ by wet area type:
| Wet area | Floor | Wall |
|---|---|---|
| Shower (enclosed) | Waterproof (full floor) | Waterproof to 1800 mm above floor substrate |
| Bath / spa | Waterproof (floor) | Water resistant 150 mm above vessel rim where within 75 mm of a wall |
| Laundry / WC | Water resistant (full floor) | Water resistant to 150 mm above the floor behind fixtures |
| Kitchen / food prep | Water resistant (floor) | Water resistant behind sink and adjacent areas |
| Balcony above habitable room | Waterproof (full floor) | Upturn to wall junction |
“Waterproof” means zero water penetration. “Water resistant” allows minor moisture movement but not bulk water entry. The two terms are defined in AS 3740 and AS/NZS 4858 (verified 2026-05-07, NCC Housing Provisions 10.2).
Membrane types and substrate compatibility
AS 3740 recognises two broad membrane categories:
Sheet-applied membranes: factory-manufactured sheets (polyethylene, PVC, bituminous). Pre-formed corners and junctions available. Generally faster on standard substrates. Substrate compatibility must be confirmed by the manufacturer.
Liquid-applied membranes: brush, roller, or spray-applied systems (polyurethane, modified bitumen, acrylic). More flexible for complex junctions and irregular substrates. Require correct wet-film thickness per manufacturer’s data sheet and sufficient cure time before flood testing. AS/NZS 4858:2004 specifies the performance requirements that membranes must meet (verified 2026-05-07, Standards Australia AS/NZS 4858).
Both types require primer where specified by the manufacturer. Substrate must be dry, clean, and structurally sound before application.
Fall to waste
The floor must fall continuously toward the waste outlet. The ABCB Housing Provisions 2022, which reflects the AS 3740 requirements, specifies the floor plane must have a minimum fall of 1:80 and a maximum fall of 1:50 to the waste (verified 2026-05-07, Housing Provisions clause 10.2.12).
On jobs with large-format tiles, achieving and maintaining the required fall through the substrate and waterproof membrane is a coordination point between the plasterer (screed bed), the waterproofer (membrane), and the tiler (tile bedding). The waterproofer does not own the screed; they verify it meets the fall before membraning.
Perimeter upturns
The membrane must turn up at every wall junction, penetration, and junction with a vertical element. The minimum upturn height per current HIA Guide to Materials and Workmanship and AS 3740-2021 is pending verified member access: [HIA-028].
The upturn must be continuous, bonded at corners, and not bridged by sealant alone unless the sealant is specified as part of the system and compatible with the membrane.
Hob heights
Where a hob is used at the shower threshold, the minimum hob height above the finished floor level per the HIA Guide and AS 3740-2021 is pending verified member access: [HIA-029].
Hob construction: the Housing Provisions specify the hob must be constructed from masonry, concrete, autoclaved aerated concrete (AAC), or extruded polyurethane foam. Timber hobs are prohibited (verified 2026-05-07, Housing Provisions 10.2). The hob itself must be waterproofed continuously with the floor membrane.
Pre-tile flood test
Before any tiles, adhesive, or bedding mortar is applied over the membrane, the completed waterproofing must pass a flood test. The test verifies the membrane is continuous and watertight before it is concealed.
The flood test involves filling the wet area to a set water depth and holding it for a specified period, then inspecting for any water penetration into the substrate or through to the space below. The exact water depth and hold time per the current HIA Guide and AS 3740-2021 clause on testing is pending verified member access: [HIA-030].
Any penetration detected during the flood test requires the membrane to be repaired and retested before tiling proceeds. The test result and date should be documented in the site file. In many states, the waterproofing contractor is required to provide a certificate confirming the flood test passed before the tiler starts.
Penetrations
Every pipe penetration, drain, waste outlet, and service penetration through the membrane requires a continuous seal using a compatible sealant or flashing collar. Gaps at penetrations are the most common single cause of waterproofing failures identified at defect inspections.
What it doesn’t cover
AS 3740 applies to domestic wet areas only. Exclusions:
- Swimming pools and spas (AS 3740 clause 1.2 explicitly excludes these; pools use AS 2783 and pool-specific waterproofing systems)
- Roofs and external building envelope (external waterproofing sits under H2 Damp and weatherproofing in the NCC, and AS 4654 for above-ground membranes)
- Commercial wet areas in Class 5-9 buildings (those fall under NCC Volume One Specification 26 and separate commercial standards)
- Below-ground waterproofing (basements, retaining walls)
- Wet areas in motor vehicles, caravans, and marine vessels
Practical implications
Who does the work
Waterproofing of domestic wet areas is licensed work in NSW, VIC, and QLD. Each state uses different licence terminology:
| State | Licence / registration | Regulator |
|---|---|---|
| NSW | Waterproofing Technician contractor licence (work over $5,000) | NSW Fair Trading (verified 2026-05-07, fairtrading.nsw.gov.au) |
| VIC | Domestic Builder (Limited to Waterproofing) registration | Building and Plumbing Commission (formerly VBA) (verified 2026-05-07, vba.vic.gov.au) |
| QLD | Waterproofing contractor licence | QBCC (verified 2026-05-07, qbcc.qld.gov.au) |
| WA, SA, TAS, NT, ACT | Licensing requirements vary; confirm with state building regulator before engaging | State building regulator |
On a residential project, the builder is responsible for ensuring waterproofing is performed by a licensed contractor and that the flood test certificate is in the build file.
Sequencing on site
The waterproofing stage sits between the substrate (screed or fibre cement sheet) and the tiling. The critical sequence:
- Substrate installed and cured (concrete slab, screed, or fibre cement sheet per AS 3740)
- Fall verified (minimum 1:80 to waste before waterproofer starts)
- Membrane applied (primer where required, membrane, upturns and corner flashings)
- Curing period (liquid-applied membranes: per manufacturer’s data sheet, typically 24-48 hours minimum before flood testing)
- Flood test passed and documented
- Waterproofing certificate issued
- Tiler starts
Sequencing errors (tiler starting before flood test, screed cut after membrane applied, penetrations added after waterproofing is complete) are the top site causes of warranty claims.
Common breaches and defect patterns
The defects that recur at PCI, at handover inspections, and in waterproofing failure claims:
| Defect | Cause |
|---|---|
| No perimeter upturns at wall junction | Membrane cut flush to floor, not turned up wall |
| Missing flood test documentation | Test skipped or not recorded |
| Wrong membrane for substrate | Liquid-applied membrane on wet or contaminated substrate; incompatible primer |
| Falls to waste incorrect | Screed laid flat, no fall, or fall to wrong direction (ponding at wall, not at waste) |
| Gaps at pipe penetrations | Sealant around penetrations not continuous, no collar used |
| Hob not waterproofed | Tiled over without continuous membrane from floor |
| Membrane applied over green screed | Screed not adequately cured; adhesion failure and membrane delamination |
| Balcony membrane not continuous with building envelope | Junction between balcony slab and wall not detailed |
Relationship to AS/NZS 4858
AS 3740 is the design and installation standard. AS/NZS 4858:2004 (Wet area membranes) is the product standard: it specifies the performance tests that a membrane product must pass to be suitable for use under AS 3740. When specifying membranes, the membrane’s technical data sheet should state compliance with AS/NZS 4858 for the intended application (interior wet area, balcony, etc.).
Source link
Standards Australia: AS 3740:2021 product page (verified 2026-05-07). The standard is paywalled. The ABCB Housing Provisions 2022 Part 10.2, which sets out the same DTS provisions, is free at ncc.abcb.gov.au.
References
- Standards Australia, AS 3740:2021 Waterproofing of domestic wet areas (product page). https://store.standards.org.au/product/as-3740-2021 (verified 2026-05-07).
- Australian Building Codes Board, Part H4 Health and amenity, NCC 2022 Volume Two. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/volume-two/h-class-1-and-10-buildings/part-h4-health-and-amenity (verified 2026-05-07).
- Australian Building Codes Board, Part 10.2 Wet area waterproofing, ABCB Housing Provisions Standard 2022. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/housing-provisions/10-health-and-amenity/part-102-wet-area-waterproofing (verified 2026-05-07).
- NSW Government, Waterproofing work (licences and registrations). https://www.nsw.gov.au/business-and-economy/licences-and-credentials/building-and-trade-licences-and-registrations/waterproofing-work (verified 2026-05-07).
- Victorian Building Authority, Domestic Builder registration (limited to waterproofing). https://www.vba.vic.gov.au/registration-and-licensing/building-practitioner-registration/domestic-builder (verified 2026-05-07).
- Queensland Building and Construction Commission, Waterproofing licence. https://www.qbcc.qld.gov.au/licences/apply-licence/available-licences/other-trade/waterproofing (verified 2026-05-07).
- Queensland Building and Construction Commission, Waterproofing done right: what you need to know in 2025. https://www.qbcc.qld.gov.au/news/waterproofing-done-right-what-you-need-know-2025 (verified 2026-05-07).
- Australian Building Codes Board, Waterproofing in houses. https://www.abcb.gov.au/ncc-navigator/waterproofing-houses (verified 2026-05-07).
Related
- NCC 2022 Volume Two, the residential building code that calls up AS 3740 under Part H4
- Waterproofing, plain-English definition of waterproofing in residential construction
- Wet area waterproofing (process), the on-site procedure for membrane application and testing
- Waterproofing membranes (materials), sheet and liquid-applied membrane types, brands, and substrate compatibility
- Waterproofer (trade), what a licensed waterproofer covers, licensing, and what to require in their quote
- Wet area substrates, substrate types (fibre cement, screed, concrete) and their compatibility with AS 3740 membranes
See also
- Screed, the levelling bed that sets the fall before the membrane goes down
- Hob, the raised threshold at a shower entry; hob heights are an AS 3740 requirement
- Perimeter upturn, the membrane turn-up at wall junctions required under AS 3740
- Flood test, the pre-tile water test that verifies membrane continuity
- Screed to fall, the screed technique used to achieve AS 3740-compliant falls to waste
- NCC waterproofing, the NCC-side view of wet area waterproofing requirements
Last updated: 2026-05-07. Verified: 2026-05-07. Quarterly review for currency: check current AS 3740 edition status at Standards Australia and confirm NCC adoption in each state.