AS 3740 Guide: Australian Waterproofing Standards
AS 3740-2021 is the Australian standard that governs waterproofing of domestic wet areas. It is the single most important document in Australian waterproofing, setting out the minimum requirements for how bathrooms, show...
AS 3740-2021 is the Australian standard that governs waterproofing of domestic wet areas. It is the single most important document in Australian waterproofing, setting out the minimum requirements for how bathrooms, showers, laundries, balconies, and other wet areas must be waterproofed. In Western Australia, compliance with AS 3740 is enforced by the WA Building Commission under the Building Act 2011. Understanding this standard helps you ensure your waterproofing project is done correctly, protects your investment, and meets the legal requirements in WA.
In This Guide
What Is AS 3740-2021?
AS 3740-2021 (Waterproofing of domestic wet areas) is published by Standards Australia and sets out the minimum requirements for waterproofing in residential buildings. The current version, published in 2021, replaced the previous 2010 edition with several significant updates. The standard covers membrane types, application methods, testing requirements, minimum heights for wall waterproofing, treatment of junctions and penetrations, and the qualifications required for waterproofing installers. It is referenced by the National Construction Code (NCC) and is therefore a legal requirement in all Australian states and territories, including Western Australia.
Key Requirements of AS 3740
The standard mandates several critical requirements. Shower floors and walls must be waterproofed to a minimum height of 1800mm (or to the ceiling in enclosed showers). Bathroom floors outside the shower must be waterproofed, with walls waterproofed to a minimum of 150mm above the finished floor level. The waterproofing membrane must extend into the floor waste and be bonded to the waste flange. All internal corners and wall-floor junctions must be reinforced with bond breaker tape or similar. The membrane must be flood-tested for a minimum period before any tiling or finishing work begins. Balconies, where water may accumulate, must also be waterproofed with appropriate membranes and drainage.
How AS 3740 Applies in Western Australia
In WA, AS 3740 is adopted through the National Construction Code and enforced by the WA Building Commission. The Building Services (Registration) Act 2011 requires that waterproofing work be carried out by registered building service contractors. This means your waterproofer must hold a valid WA building registration. After completing the waterproofing, the contractor must issue a waterproofing certificate confirming the work meets AS 3740 standards. This certificate is a legal document required for building approval sign-off. The WA Building Commission can investigate complaints about non-compliant waterproofing and take action against unregistered or non-compliant contractors.
Changes in the 2021 Edition
The 2021 update to AS 3740 introduced several important changes from the 2010 edition. The definition of wet areas was clarified and expanded. Requirements for waterproofing of external wet areas (balconies, podium decks) were strengthened. The standard now provides clearer guidance on membrane testing and certification. There are updated provisions for waterproofing over timber substrates, which is relevant for many Perth homes with timber-framed wet areas. The 2021 edition also includes improved guidance on waterproofing around floor wastes and penetrations, addressing some of the most common failure points in residential waterproofing.
Common AS 3740 Compliance Failures
The most common compliance failures found in Perth homes include insufficient membrane height on shower walls (not reaching 1800mm), inadequate treatment of wall-floor junctions without proper bond breaker, membrane not bonded to the floor waste flange, shower hobs too low or missing entirely, insufficient curing time before tiling, and failure to flood-test the membrane before covering. These failures are often the root cause of leaking showers and wet area problems. During Perth's construction boom, rushed timelines sometimes led to these corners being cut, which is why homes built between 2005 and 2015 are now seeing higher rates of waterproofing failure.
What This Means for Perth Homeowners
As a Perth homeowner, understanding AS 3740 helps you in several ways. When getting quotes for waterproofing work, you can verify that contractors intend to comply with the standard. You can ask about flood testing, membrane heights, and certification. For pre-purchase inspections, you can check whether the property's waterproofing appears to meet AS 3740 requirements. If you are renovating, you know that waterproofing is not optional — it is a legal requirement that must be performed by a registered contractor in WA. And if you experience waterproofing problems, understanding the standard helps you identify whether the original work was deficient, which may support warranty claims or complaints to the WA Building Commission.
WA Compliance Reminder
All waterproofing work in Western Australia must be performed by contractors registered with the WA Building Commission under the Building Services (Registration) Act 2011. We connect you with verified, licensed Perth waterproofing contractors who meet all WA compliance requirements.
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