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Waterproofing of wet areas - The basics
Waterproofing defects are often cited as one of the major defect areas in buildings.
The cost of repair from waterproofing failures is disproportionate to the cost to correctly install appropriate materials and systems during construction.
In many cases, repairs can only be undertaken in piece-meal fashion and destructive methods are used to reapply shortfalls in appropriate membranes and waterproofing systems.
Water damage not only contributes to damp, mould and rot, but can affect the structural integrity of flooring and walls; with dangerous flow-on effects to electrical components, structural steel, fixings and roof strapping ties.
Most jurisdictions across Australia recognise that ongoing preventative maintenance is required by home-owners for grout, sealants and junctions.
However, installers and practitioners are still obligated to provide a statutory warranty for all work undertaken and the periods for defect liability are found in the relevant Acts, Regulations, Standards or the Contract itself.
Hence it is extremely important that you have a thorough understanding of the NCC and Australian Standards provisions for waterproofing of wet areas.
To assist building practitioners and supervisors with easy-to-find compliance options, this information details the Deemed-to-Satisfy outcomes available for the waterproofing of wet areas for Class 1 buildings.
Deemed-to-satisfy solution or performance solution?
Deemed-to-satisfy methods for waterproofing of wet areas are detailed within the National Construction Code (NCC) 2019 Volume Two, Part 3.8.1.2 – which through Table 3.8.1.1 lists out the extent of waterproofing required in wet areas and sets out what elements need to be waterproof or water resistant as a minimum in meeting the requirements of the NCC.
In turn the NCC references Australian Standard (AS) 3740 - Waterproofing wet areas within residential buildings which sets out the means for which waterproofing must be undertaken in meeting the Deemed-to-Satisfy provisions of the NCC.
This means that for as part of a Deemed-to-Satisfy solution, all waterproofing of wet-areas must follow the NCC provisions for the ‘where’ and then the requirements of AS 3740 for the ‘how’.
It is important to remember that if a prescriptive Deemed-to-Satisfy method is modified or an alternate method is used during design and construction of wet-areas, the proposed method(s) undertaken can only be a done via Performance Solution and must demonstrate compliance with the listed Performance Requirements of the NCC.
Compliance with Performance Requirements are outlined with a Performance Based Design Brief (PBDB) for certification by a building surveyor as part of a building permit application. It is generally not acceptable to permit authorities for a practitioner or surveyor to detail a Performance Solution ‘after the fact’ unless due to unforeseen, or in very limited, circumstances.
What does the NCC outline?
NCC 2019, Volume 2, Part 3.8.1.2 prescribes compliance with Table 3.8.1.1. This Table details which substrates, surfaces, penetrations and junctions must be water resistant or waterproof as defined within the NCC itself; being:
- water resistant - means the property of a system or material that restricts moisture movement and will not degrade under conditions of moisture; and
- waterproof - means the property of a material that does not allow moisture to penetrate through it.
A substrate is typically a floor or wall structure, which is different from a surface being the face of a floor or wall that has actual contact with water or moisture. A junction is where a wall meets a floor or wall – and a penetration is a hole (typically) in a substrate or surface material for taps, floor wastes, inspection openings etc.
What does AS 3740 outline?
AS 3740 details material considerations for different required outcomes, as well as the required properties of most materials and their use.
Floor grades and wastes are specified for different exposure locations of a wet area, including where those wastes are required and their construction requirements. It also provides for sections and diagrams for construction detailing.
Waterproof membrane installation is also covered in detail (both internal and external) and includes connection requirements for drainage penetrations, junctions, step-downs and door opening considerations.
AS 3740 is a comprehensive and detailed document that should form part of the reference toolkit for any practitioner, surveyor or supervisor involved with the design and construction of Class 1 building wet-areas.
What else should you consider?
Other standards may be called up for consideration when designing or constructing wet-areas, especially through AS 3740. For example:
- HB 161 – Guide to Plastering is considered for screeds and flexible rendering;
- AS 3700 is applied for Masonry substrates, and
- AS 1684 series for construction of structural plywood substrates.
Some of these standards have additional prescriptions within them as part of their wider considerations for application. For example,
- AS 3958.1 Guide to the installation of ceramic tiles states at Appendix A – Admixtures (A9), that;
“…integral waterproofing admixtures (to render) should not be considered as an alternative to the membranes otherwise specified…”
This means that adding a water-proofing admixture to a screed or render may be used in conjunction with a waterproof membrane, but not replace it, subject to its suitability at A9 (f). This is a particularly important consideration for practitioners applying waterproofing over render float-coats to masonry walls.
It’s also important to note that a state or local jurisdiction may have additional requirements over AS 3740. For example, a floor waste may not be required in AS 3740 but be prescribed by a particular jurisdiction - which would constitute a required waste and trigger AS 3740 requirements. Conversely, South Australia vary-out the requirement for a floor waste subject to certain conditions at Part 3.8.1 of the NCC.
Need more information?
HIA provide a number of information sheets regarding waterproofing and are linked below:
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