What Is AS 3740 and Why Does It Matter?
AS 3740 is the Australian Standard for waterproofing of domestic wet areas. It sets out the minimum requirements for waterproofing in bathrooms, showers, laundries, and other areas where water is regularly used. In South Australia, compliance with AS 3740 is mandatory under the National Construction Code (NCC), and non-compliant work can result in defect notices, insurance claims being rejected, and significant remediation costs.
For Adelaide homeowners planning a renovation, understanding AS 3740 requirements before work begins can save thousands of dollars and months of frustration. The standard covers everything from which areas must be waterproofed to the testing requirements that must be met before tiling can commence.
Wet Area Classifications Under AS 3740
The standard classifies bathroom areas based on their exposure to water. A shower recess is the highest-risk zone — the floor and walls to a minimum height of 1800mm (or the height of the shower rose, whichever is greater) must be fully waterproofed. The remainder of the bathroom floor must also be waterproofed if it is within 1500mm of a shower, bath, or basin without a splash guard.
Bath surrounds require waterproofing on the walls to at least 150mm above the rim of the bath, extending 150mm beyond the outer lip. Vanity areas require protection against splashing but not full membrane coverage. These distinctions matter because over-specifying costs money, while under-specifying causes leaks.
Membrane Requirements and Testing
AS 3740 does not mandate a specific membrane product, but it does require that the membrane system used meets AS 4858 (for liquid-applied membranes) or AS 4654.1 (for sheet membranes). The membrane must be applied at the manufacturer's specified thickness — typically 1.0mm to 1.5mm for liquid-applied systems — and must bond properly to the substrate.
Before tiling, a flood test (also called a water test) must be carried out. The waterproofed area is filled with water to a minimum depth of 25mm and left for at least 24 hours. No drop in water level is acceptable. A qualified bathroom waterproofer will document this test and issue a compliance certificate.
Common Compliance Failures in Adelaide
Based on reports from Adelaide building inspectors, the most frequent AS 3740 compliance failures include inadequate membrane thickness at corners and junctions, missing or poorly applied reinforcing tape, insufficient wall height coverage in shower recesses, and failure to carry out flood testing. These issues often appear years later as leaking showers or mould growth behind tiles.
The best protection against compliance failures is hiring a licensed waterproofer who specialises in wet area waterproofing and can provide photographic evidence of each stage of the process.
Getting Compliant Waterproofing in Adelaide
If you are renovating a bathroom in Adelaide, insist on AS 3740 compliance from the outset. Ask your waterproofer for a written specification, verify their licence with Consumer and Business Services SA, and request a waterproofing certificate before tiling commences.
To compare licensed waterproofers in your area, use our Find a Waterproofer tool. For a breakdown of how much compliant bathroom waterproofing typically costs, see our bathroom waterproofing cost page.
You might also find our guide on how to waterproof a bathroom helpful for understanding the full process from start to finish.