Building for the long-term: the vital importance of compliant waterproofing in residential properties

Authored by Troy Creighton, Stormtech managing director

Waterproofing is critical for wet areas such as bathrooms, laundries, and kitchens to protect buildings from water damage and maintain occupants' health. However, it has become common to only strive for bare minimum building requirements. To keep our buildings and occupants safe, the real objective for any construction project should not only be meeting the material, design and installation requirements for waterproofing wet areas, but exceeding them.

Bare minimum waterproofing may achieve building compliance but if it is not done correctly it can be more prone to deterioration or cause damage in the future. This can lead to costly repairs that could have been avoided. Poor waterproofing, of course, creates a myriad of short-term problems like mildew and mould growth, and can lead to cracks or concrete cancer that impacts structural integrity. Government research on serious building defects in New South Wales strata communities found that the most commonly occurring defect was related to waterproofing, affecting 23 per cent of surveyed buildings.

The importance of quality waterproofing the 2021 version of the Australian Standards 3740 (AS 3740-2021) “waterproofing of wet areas within residential buildings” and the 2022 update of the national construction code (NCC 2022) must be taken into careful consideration.

The new NCC provisions focus on the waterproofing of wet areas and the waterproofing of external walls, as well as changes to gradient requirements for surface finishes and new requirements around pipe sizing. There is also a new requirement for lead-free plumbing products designed to improve the long-term health of all Australians. From September 1, 2025, only products WaterMark certified conforming to the lead-free provisions will be authorised for use in plumbing installations.

NCC 2022 now also references AS 3740 for waterproofing domestic wet areas, which aims to align with current waterproofing practices. As a result, AS 3740 has been restructured into four sections to better address the standards for waterproofing residential wet areas:

· Section 1: scope, definitions, and other specific normative reference documents.

· Section 2: design principles that apply to the standard.

· Section 3: requirements for acceptable materials to be used in waterproofing wet areas.

· Section 4: details for the installation of waterproof and water-resistant materials to be used in domestic wet areas.

The latest edition of AS 3740 has introduced significant revisions, including a categorisation of domestic wet areas into three levels based on the potential risk of water or moisture causing unhealthy and hazardous conditions or damage to the building structure:

· Category 1: wet areas (high risk) include enclosed and unenclosed shower areas, baths with unenclosed showers over them, any area within reach of a hand-held shower fitting, water closets with a hand-held douche spray, and dedicated douche rooms.

· Category 2: wet areas (moderate risk) include the bathroom area outside an unenclosed shower area and the bathroom area outside of the unenclosed shower over the bath.

· Category 3: wet areas (low risk) include any wet area without a shower.

Legislative ambiguity has created confusion around which waterproofing standards apply, leading to uncertainty around compliance. For example, while AS 3740 sets a minimum fall of 1:100 for areas adjacent to the shower, the NCC 2022 volume two, combined with liveable housing provisions, mandates a minimum fall of 1:80.

There is a lack of detail in AS 3740 regarding the area of adhesion for leak control flanges, so it is important for installers to understand that most membrane manufacturers require a minimum of 50mm as the area of adhesion (basically the same as a floor/wall joint). Using leak control flanges with areas of adhesion narrower than 50mm may void a waterproofing material’s warranty.

A sure-fire way of meeting and exceeding the minimum standards set by the NCC and AS 3740 is to seek advice from waterproofing and drainage experts, who can review the project from an experienced perspective select high-quality waterproofing products and carry out a suitable installation.

Experts, such as those with extensive experience in linear drainage solutions, can provide valuable guidance on these factors, ensuring that the project is not only compliant but also cost-effective overall. By prioritising the quality of the waterproofing system, builders, architects, and contractors can mitigate the risks of building defects and provide a durable and safe structure for homeowners, tenants, and strata managers.

Troy Creighton has been the managing director of Stormtech Pty Ltd since 2003. Stormtech was founded by Troy’s father, John, in 1989 and Troy has been involved in the design and functionalities of linear drains ever since. Having worked with John for some time, Troy wanted to further his career in a corporate environment, holding several sales and marketing positions for a number of building materials companies. After re-joining Stormtech in 2003, Troy has developed the company into the market leading architectural drainage solutions company in Australia and expanded extensively into overseas markets.

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