Australian Standard AS 3740 is the definitive technical document governing waterproofing of domestic wet areas in Australia. For Sydney homeowners, builders, and renovators, understanding this standard is essential — it dictates how bathrooms, laundries, showers, and other wet areas must be waterproofed to comply with the National Construction Code (NCC). In this guide, Waterproofing Sydney provides a clear, practical explanation of AS 3740 and what it means for your project.
What Is AS 3740?
AS 3740 — formally titled “Waterproofing of domestic wet areas” — is an Australian Standard published by Standards Australia. It sets out the requirements for waterproofing membranes in residential wet areas, including bathrooms, showers, laundries, toilets, and any other domestic room where water is used and may contact floors or walls.
The standard specifies where waterproofing membranes must be applied, how they must be installed, what materials are acceptable, and the performance requirements the finished membrane must meet. It is referenced by the NCC (Volume 2 for residential buildings), which means compliance with AS 3740 is a legal requirement for all new construction and renovation work in NSW.
The current edition is AS 3740:2021, which replaced the 2010 version and introduced several important updates. If your home was built or renovated before 2021, the waterproofing may comply with an earlier edition but should still meet the fundamental requirements of the standard.
Where Does AS 3740 Require Waterproofing?
AS 3740 divides wet areas into zones based on their exposure to water, and specifies different waterproofing requirements for each zone. Understanding these zones is critical for any bathroom renovation or new build in Sydney.
| Area | Floor Waterproofing | Wall Waterproofing | Key Requirements |
|---|---|---|---|
| Shower recess (enclosed) | Required — full floor area | Required — full height of walls within shower | Membrane must extend at least 150mm beyond shower screen line on floor; walls waterproofed to full height within shower enclosure |
| Bathroom floor (outside shower) | Required — full floor area | Required — minimum 150mm above finished floor level on all walls | Step-downs or hobless thresholds must comply with specific detailing requirements |
| Bath area | Required — full floor area | Required — minimum 150mm above rim of bath on adjacent walls | Walls behind taps waterproofed to tap height plus 150mm |
| Laundry | Required — full floor area | Required — minimum 150mm above finished floor level | Behind and beside washing machine and trough: 150mm above appliance connection point |
| Toilet (separate room) | Required — full floor area | Required — minimum 150mm up walls | Floor membrane must turn up at all wall junctions |
| Balconies over habitable rooms | Required — full floor area | Required — minimum 150mm up abutting walls | Must include drainage falls and appropriate flashing details |
Key Requirements of AS 3740:2021
The 2021 edition of AS 3740 introduced several important changes and clarifications. Here are the key requirements that affect most Sydney residential projects:
- Full floor waterproofing: All wet area floors must be waterproofed in their entirety, with the membrane turning up at all wall and floor junctions by a minimum of 150mm.
- Shower wall requirements: Walls within an enclosed shower must be waterproofed to the full height of the wall. This is a change from the 2010 edition, which allowed waterproofing to 1,800mm in some configurations.
- Hobless shower detailing: The standard provides specific requirements for hobless (step-free) shower designs, which are increasingly popular in Sydney bathroom renovations and essential for accessible design. The membrane must extend at least 150mm beyond the shower screen line, and appropriate drainage gradients must be maintained.
- Membrane bond strength: The membrane must achieve and maintain adequate bond strength to the substrate to ensure long-term performance. This requirement emphasises proper substrate preparation — clean, dry, and structurally sound surfaces.
- Junction details: The standard specifies detailed requirements for membrane treatment at junctions between floors and walls, around penetrations (pipes, drains), and at changes in substrate material. These junctions are the most common failure points in waterproofing systems.
- Material compatibility: All components of the waterproofing system — primers, membranes, bond breakers, sealants, and adhesives — must be compatible with each other and with the substrate. Mixing products from different manufacturers is generally discouraged unless compatibility has been confirmed.
Common AS 3740 Compliance Failures in Sydney
As specialists who regularly assess waterproofing failures across Sydney, Waterproofing Sydney sees certain compliance issues repeatedly:
- Insufficient wall height: Waterproofing membranes that stop short of the required height, particularly in shower recesses. This is one of the most common defects we identify.
- Poor junction treatment: Inadequate detailing at floor-wall junctions, around shower grates, and at pipe penetrations. These are the points where water finds its way through the membrane.
- Inadequate substrate preparation: Membranes applied over dusty, damp, or uneven substrates that prevent proper adhesion. The membrane may appear intact initially but fails within months or years.
- Missing waterproofing under baths: Some installers omit waterproofing beneath freestanding or built-in baths, assuming the bath itself will contain all water. Leaking bath wastes and overflow connections can cause significant concealed damage.
- Incorrect membrane thickness: Liquid-applied membranes must achieve minimum dry film thickness (typically 1.0–1.5mm depending on the product). Insufficient application thickness reduces the membrane’s effectiveness and longevity.
- No waterproofing certificate: Failure to provide a waterproofing certificate upon completion. This document is essential for compliance verification and future property transactions.
AS 3740 and Bathroom Renovations
If you are renovating a bathroom in Sydney, AS 3740 applies to your project regardless of whether you are performing a full gut renovation or a partial update. Any work that disturbs or removes the existing waterproofing membrane triggers the requirement to re-waterproof to the current standard.
This has important implications:
- Removing floor tiles in a bathroom requires complete re-waterproofing of the floor and wall turn-ups
- Changing shower screen location or configuration may require extending the membrane
- Installing a new shower over a bath requires waterproofing the walls to full height within the shower zone
- Converting a bath to a walk-in shower requires full re-waterproofing to current standards
Under the NSW Home Building Act 1989, waterproofing is classified as specialist work. In NSW, only licensed waterproofers (holding the appropriate NSW Fair Trading licence) are permitted to perform waterproofing work on residential buildings. General builders and tilers cannot legally perform waterproofing unless they hold the specific waterproofing licence endorsement.
The Inspection and Certification Process
Compliance with AS 3740 must be verified through inspection and certification. The typical process in NSW involves:
- Substrate preparation inspection: The certifying authority (private certifier or council) may inspect the substrate before membrane application to verify it is clean, dry, and appropriately prepared.
- Membrane application: The licensed waterproofer applies the membrane system in accordance with the manufacturer’s specifications and AS 3740 requirements.
- Flood testing: Upon completion, the waterproofed area is flood-tested by filling it with water to a depth of approximately 25mm and holding the water for a minimum of 24 hours. No leakage is permitted.
- Certification: Following a successful flood test, the waterproofer issues a waterproofing certificate (also known as a Form 4.1 or manufacturer’s warranty certificate). This document certifies that the waterproofing has been applied in accordance with AS 3740 and the membrane manufacturer’s specifications.
- Certifier inspection: The certifying authority inspects the completed waterproofing and reviews the certificate before approving the next stage of construction (typically tiling).
AS 3740 and the National Construction Code
The relationship between AS 3740 and the NCC is important to understand. The NCC sets performance requirements for buildings — it states what outcomes must be achieved. AS 3740 is a “deemed-to-satisfy” solution referenced by the NCC — it describes one way to achieve the NCC’s performance requirements.
In practice, this means that complying with AS 3740 is the most straightforward path to NCC compliance for wet area waterproofing. Alternative solutions are theoretically possible under the NCC’s performance-based framework, but they require engineering assessment and certification to demonstrate equivalent performance — a path rarely taken for standard residential work.
Choosing a Waterproofer Who Understands AS 3740
Not all waterproofers deliver the same standard of work. When selecting a waterproofing contractor for your Sydney project, verify the following:
- Current NSW Fair Trading licence for waterproofing work
- Demonstrated knowledge of AS 3740:2021 requirements
- Use of quality membrane products from reputable manufacturers
- Willingness to conduct flood testing and provide a formal waterproofing certificate
- Comprehensive warranty coverage — both the installer’s workmanship warranty and the membrane manufacturer’s product warranty
- Clear documentation and photography of the membrane installation before tiling
Frequently Asked Questions
Does AS 3740 apply to existing bathrooms that are not being renovated?
AS 3740 applies to new construction and renovation work. If you are not altering your existing bathroom, there is no legal requirement to upgrade the waterproofing to current standards. However, if your existing waterproofing is failing (evidenced by leaks, water damage, or mould), remedial waterproofing should comply with the current edition of AS 3740.
Is waterproofing under tiles sufficient without a separate membrane?
No. Tiles and grout are not waterproof — they are water-resistant at best. Water penetrates through grout lines, around fixtures, and through any cracks in tiles. A compliant waterproofing membrane beneath the tiles is essential and required by AS 3740. The membrane is the true waterproofing barrier; tiles are the wearing surface.
Can I waterproof my own bathroom in NSW?
Under the NSW Home Building Act 1989, waterproofing of wet areas in residential buildings must be performed by a person holding the appropriate waterproofing licence issued by NSW Fair Trading. Owner-builders may perform their own waterproofing but must still comply with AS 3740 and obtain the necessary inspections and certifications. Contact Waterproofing Sydney for licensed, certified waterproofing services.
What happens if my waterproofing does not comply with AS 3740?
Non-compliant waterproofing is a building defect. Under the NSW Home Building Act 1989, it constitutes a major defect subject to a six-year statutory warranty period. If your waterproofing fails within this period, the licensed contractor who performed the work is legally obligated to rectify it. Non-compliant waterproofing can also prevent the issue of an occupation certificate for new builds or renovations.
How long does waterproofing membrane last?
Quality waterproofing membranes installed in compliance with AS 3740 are designed to last the lifetime of the tiled installation — typically 15–25 years or longer. The membrane itself does not wear out under normal conditions; failures are almost always attributable to installation defects, substrate movement, or damage during subsequent work. This is why correct installation by a licensed professional is so important.
Planning a bathroom renovation in Sydney? Waterproofing Sydney ensures full AS 3740 compliance on every project, backed by comprehensive certification and warranties. Get in touch today for expert waterproofing that protects your investment.