Bathrooms
Bathroom waterproofing: what every homeowner needs to know
Understand the waterproofing requirements for Australian bathrooms, including regulations, methods, and how to ensure the job is done right.
Why waterproofing matters
Waterproofing is arguably the most critical step in any bathroom renovation. Inadequate waterproofing leads to water penetrating the building structure, causing timber rot, mould growth, and structural damage that can cost tens of thousands of dollars to repair. In multi-storey buildings, water damage from a poorly waterproofed bathroom can affect units below, leading to significant liability.
Australian waterproofing standards
Waterproofing in wet areas must comply with Australian Standard AS 3740. This standard specifies minimum requirements for areas that are subject to water exposure. In most states, waterproofing must be carried out by a licensed waterproofer, and the work must be inspected and certified before tiling can commence. The Building Code of Australia (BCA) references these standards and sets them as the minimum benchmark.
What areas need waterproofing
The standard requires waterproofing on all shower floors and walls to a height of at least 1800mm (or to ceiling height if a shower screen does not contain water splash). Floor areas around baths, basins, and toilets also require waterproofing. The waterproofing membrane must extend at least 150mm up the walls in these areas. For step-down showers, the membrane must continue under the step and up both sides. Any penetrations through waterproofed surfaces (like pipe entries) must be sealed with appropriate flanges.
Waterproofing methods and materials
The most common waterproofing method for residential bathrooms is liquid-applied membranes — typically a two-coat system applied with a roller or brush. These membranes are flexible, easy to apply, and effective when applied correctly. Sheet membranes are used in high-risk areas or where additional protection is needed. Both types must meet the requirements of AS 4858. The waterproofing system should include reinforcing fabric at all corners, joints, and penetrations where cracking is most likely to occur.
Ensuring quality workmanship
Always verify that your waterproofer holds the appropriate license for your state. Request a certificate of waterproofing compliance once the work is complete. Good waterproofers will invite inspection of the membrane before tiling begins — if yours does not, ask to inspect the work yourself. Look for consistent membrane thickness, properly sealed corners and penetrations, and no visible gaps or thin spots. A flood test (filling the shower base with water for 24 hours) is good practice to verify the membrane integrity before tiling.