AS waterproofing code explained for Australian wet areas

What the AS waterproofing code means

In Australian building work, the search phrase AS waterproofing code usually refers to AS 3740:2021, Waterproofing of domestic wet areas. It is not a standalone building code in the same sense as the National Construction Code. It is an Australian Standard used to design and install waterproofing systems in domestic wet areas such as showers, bathrooms, laundries and sanitary compartments.

The purpose is practical: water needs to be contained within the intended wet area and kept away from framing, linings, floors and other building elements that can be damaged by moisture. AS 3740 helps set out how that protection is achieved, but it must be read in the correct regulatory context.

For Australian projects, the key relationship is between AS 3740:2021 and the NCC. The NCC sets mandatory performance and Deemed-to-Satisfy requirements once adopted by a state or territory. AS 3740:2021 is one recognised pathway for wet area construction, but the exact obligation depends on the relevant NCC volume, building class, jurisdiction, approval date and any state or territory variation.

This article focuses on internal wet areas and the publicly described role of AS 3740:2021 in NCC wet area compliance. It does not cover external membranes for roofs, balconies, podiums or below-ground structures, which are subject to different requirements and standards.

AS 3740:2021 in context

Standards Australia identifies AS 3740:2021 as the fifth edition of Waterproofing of domestic wet areas. Public catalogue information lists its publication date as 23 July 2021 and describes the standard as setting minimum requirements for the materials, design and installation of waterproofing for domestic wet areas. The 2021 edition superseded AS 3740-2010 and its amendment.

The word minimum is important. A wet area can still be defective even when the membrane product is marketed as suitable. Performance depends on the whole system: substrate preparation, falls, junctions, penetrations, bond breakers, curing, product compatibility and workmanship. On higher-risk projects, a designer may also specify a more conservative detail than the minimum, for example on timber-framed floors, wet-room layouts, large-format tile installations, high-use bathrooms or wet areas above habitable rooms.

For readers comparing building requirements across countries, AS 3740 is an Australian Standard. Similar issues may be dealt with elsewhere through plumbing codes, building regulations, manufacturer installation standards, tile industry manuals or insurance guidance. The terminology can look familiar, but the compliance pathway is jurisdiction-specific.

How AS 3740 works with the NCC

The NCC is performance-based. It allows compliance through a Performance Solution, a Deemed-to-Satisfy Solution, or a permitted combination of both. For houses and other Class 1 buildings, the relevant wet area provisions sit in NCC Volume Two and the ABCB Housing Provisions. ABCB guidance describes AS 3740 as a Deemed-to-Satisfy route for wet area construction, provided the specified Housing Provisions clauses are also satisfied. The Housing Provisions also contain detailed construction provisions that can be used as an alternative DTS route.

A simple way to view the relationship is this: the NCC sets the required level of building protection, while AS 3740 can provide a recognised method for designing and installing the waterproofing system. Since NCC 2022, more wet area construction details have been placed back into the Housing Provisions, so practitioners should not assume that AS 3740 is the only document to check.

ABCB guidance also warns against casually mixing provisions from AS 3740 and the Housing Provisions when using a DTS pathway. A design team should select and document a clear compliance route instead of taking isolated details from different pathways because they appear convenient.

Where wet area waterproofing applies

The NCC definition of wet area covers areas within a building that are supplied with water, including bathrooms, showers, laundries and sanitary compartments. It excludes kitchens, bar areas, kitchenettes and domestic food and beverage preparation areas. That exclusion often surprises homeowners, but it does not mean kitchens can ignore moisture risk. It means they are not treated as wet areas under the same NCC wet area provisions.

For houses, the Housing Provisions separate requirements by location and risk. The most demanding provisions are usually around showers because they are exposed to regular direct wetting. The floor of a shower area with a hob, step-down or level threshold must be waterproof, and the shower walls must be waterproof to at least 1800 mm above the floor substrate. Wall junctions, wall/floor junctions and penetrations within the shower area also require waterproof treatment.

Outside the shower area, requirements change with the substrate. Public NCC material states that concrete, compressed fibre-cement and fibre-cement sheet floors outside the shower area are treated differently from timber floors, including particleboard and plywood. Timber-based floors carry higher moisture risk and are generally required to be waterproof rather than merely water resistant in those locations.

Baths, spas, laundries, WCs and other vessels have their own rules. For example, wall areas near a laundry tub or basin may need water-resistant treatment where the vessel is close to a wall, while tap and spout penetrations can require waterproof treatment. WC areas with handheld bidet sprays have additional waterproofing requirements. Details also differ between building classes and NCC volumes, so a Class 1 house detail should not automatically be copied into a Class 2 apartment or commercial building.

Waterproof and water resistant are not the same

A common wet area design error is treating waterproof and water resistant as interchangeable. They are different levels of protection. Waterproof elements are intended to stop water passing through. Water-resistant elements resist moisture, but they are not necessarily a complete barrier under ongoing wetting.

That distinction affects material selection. NCC housing provisions list membranes complying with AS/NZS 4858 among materials deemed waterproof, together with other options such as stainless steel, waterproof sealant and flexible waterproof sheet flooring with waterproof joints. For water-resistant construction, the acceptable materials and substrates are different and may depend on using a suitable surface material together with a suitable substrate.

This is why tiles alone are not a waterproofing system. Tiles and grout may shed water, but grout joints, movement joints and penetrations do not perform like a continuous membrane. A compliant wet area relies on a complete system behind or below the visible finish. The finish may help protect the system, but it does not replace the membrane, flashing, waterstop, sealed joint or substrate requirement. See also: Membranes.

Design details that decide compliance

Most waterproofing failures are not caused by the general concept of waterproofing. They occur at transitions: wall/floor junctions, shower thresholds, doorways, drains, hob corners, pipe penetrations, bath lips, preformed shower bases and substrate joints. These details should be resolved before tiling begins.

Falls are another critical item. Under the NCC Housing Provisions, where a floor waste is installed, the floor plane must fall continuously to the waste within stated limits. Public NCC text identifies a minimum continuous fall of 1:80 and a maximum continuous fall of 1:50. This is not only a drainage preference. Poor falls can leave ponding water, increase membrane exposure, stain finishes, encourage mould and create disputes about whether the shower or bathroom performs as intended.

Preformed shower bases and baths need careful coordination with wall linings. The Housing Provisions require preformed shower bases to have an upturn lip, be recessed into the wall so water-resistant materials pass inside the lip, and be supported to prevent distortion or cracking. Similar principles apply to non-freestanding baths and spas, where the lip and wall interface must shed water into the vessel, not into the framing.

Before membrane application, the substrate should be checked for cleanliness, stability, moisture condition, surface profile and compatibility with primers and sealants. Movement joints and bond breakers must be installed as part of the waterproofing system, not improvised after tiling starts. Product data sheets should be read alongside the selected compliance pathway because a product can meet a standard and still be misused on a particular substrate, at the wrong thickness, in unsuitable curing conditions or outside its intended exposure.

What changed after NCC 2022

The main shift for wet area users was not simply that AS 3740:2021 replaced the 2010 edition. NCC 2022 also reorganised and expanded the way wet area waterproofing details appear in the code framework. ABCB guidance explains that earlier NCC editions had moved many construction details out of Volume Two, leaving the NCC to state what needed protection while AS 3740 described how. NCC 2022 brought many details back into the Housing Provisions while still allowing AS 3740 as a pathway where the NCC permits.

For project teams, that changed the checking process. A specification that simply says comply with AS 3740 may not be enough if the relevant NCC provisions also impose specific requirements for falls, shower classification, materials, thresholds or state variations. A drawing detail copied from an older project may also refer to AS 3740-2010 or to an older NCC clause number, which can create confusion during certification.

There is also a timing issue. NCC 2022 was adopted from 1 May 2023, Amendment 1 was adopted from 1 May 2025, and Amendment 2 from 29 July 2025. NCC 2025 has been published for jurisdictional consideration, and adoption depends on state and territory implementation. Therefore, a project in September 2026 should confirm the applicable NCC edition with the relevant building authority, certifier or surveyor before finalising wet area details.

For more technical-code explainers, see the Standards section.

Practical checklist for designers, builders and inspectors

• Identify the building class and the applicable NCC volume before selecting the wet area pathway.
• Confirm the adopted NCC edition and any state or territory variation for the project approval date.
• State clearly whether the DTS pathway relies on AS 3740:2021, the Housing Provisions, or another approved approach.
• Classify each wet area: shower, area outside shower, bath or spa zone, laundry, WC, sanitary compartment or other vessel area.
• Distinguish waterproof elements from water-resistant elements on drawings and schedules.
• Check substrate type, especially timber-based floors, because it can change the required level of protection.
• Resolve falls to wastes, thresholds, hobs, step-downs, preformed bases and door openings before waterproofing starts.
• Detail penetrations, wall/floor junctions, wall junctions, niches and fixtures before membrane application.
• Use membrane, primer, sealant, tape and accessory products within the same tested or compatible system where required by the manufacturer.
• Keep records: product data sheets, batch details, substrate checks, application dates, curing times, photographs and waterproofing certificates where required.

Frequently asked questions

Is AS 3740 mandatory for every bathroom in Australia?

Not in that simple form. AS 3740:2021 is a key Australian Standard for domestic wet area waterproofing and is used as a recognised DTS pathway under the NCC where permitted. The legal obligation comes through the NCC as adopted by each state or territory, plus any local building regulations and project approvals.

Does a kitchen need waterproofing under AS 3740?

Kitchens, kitchenettes, bar areas and domestic food preparation areas are excluded from the NCC wet area definition used for these waterproofing provisions. Designers may still specify moisture protection behind sinks, dishwashers or splashbacks for durability, but that is different from treating the kitchen as a wet area under AS 3740-style domestic wet area provisions.

Can a builder combine AS 3740 and the Housing Provisions?

For a Deemed-to-Satisfy solution, the safer approach is to choose and document the permitted pathway rather than mixing isolated clauses. ABCB guidance indicates that AS 3740 can be used as a DTS pathway only with specified NCC Housing Provisions also satisfied. Project-specific interpretation should be confirmed with the certifier or surveyor.

Are tiles enough to waterproof a shower?

No. Tiles are a finish, not a complete waterproofing system. A shower typically needs the correct substrate, membrane or other waterproof material, sealed junctions, treated penetrations, compliant falls and compatible installation products. Grout and tiles do not replace the required waterproofing layer.

Who should confirm compliance on a real project?

The responsible designer, builder, waterproofing installer and building certifier or surveyor should each check the parts relevant to their role. For licensing, certificates and inspection requirements, always check the state or territory rules that apply to the project location.