Not by itself. AS 3740 is a standard, but the National Construction Code calls it up, and the Code has legal force through state building legislation. The practical effect is the same. Waterproofing a domestic wet area that does not comply with AS 3740 is non-compliant building work.

What is the current version of AS 3740?

The standard has been revised several times, most recently in 2021. Any work being done now should be to the current edition. If a quote references an older version, that is worth asking about.

Does AS 3740 apply to a bathroom I am only partly renovating?

If the work disturbs the existing waterproofing, yes. Replacing a shower screen may not, but retiling, moving a waste, or removing wall sheeting all breach the membrane and the wet area then has to be brought up to standard.

AS 3740 Explained: What the Waterproofing Standard Actually Says

If you are getting quotes for a bathroom, you will see AS 3740 referenced and probably not explained. It is worth understanding, because it is the difference between a wet area that complies and one that does not.

What AS 3740 is

AS 3740 is the Australian Standard titled Waterproofing of domestic wet areas. It sets out where waterproofing must be applied in a home, how it must be detailed, and what the materials have to be capable of.

It is not optional. The National Construction Code references AS 3740, and the Code carries legal force through state building law. A bathroom waterproofed outside the standard is defective building work, regardless of how good it looks when the tiler leaves.

What counts as a wet area

Broader than most people assume. The standard covers bathrooms and ensuites, laundries, and toilets, and it treats different zones within those rooms differently. A shower enclosure has far more demanding requirements than the corner of a laundry, because of how much water actually lands there.

Where the membrane has to go

The requirements vary with the construction type, but in general terms:

Shower areas. The entire floor of the shower, without exception. The walls of the shower enclosure to a substantial height, typically 1800mm above the floor. All the internal corners and the wall-to-floor junction.

The rest of the room. Wall and floor junctions throughout the wet area. Walls to a minimum height above floor level, commonly 150mm, so splashing and mopping do not get into the sheeting.

Around baths and basins. The vertical surfaces adjacent to any vessel, and the junction where the vessel meets the wall.

Hobs, steps and niches. Fully, including every internal corner. A shower niche is a box cut into a wet wall and it needs treating as carefully as the floor.

Penetrations. Anywhere something passes through the membrane, which means the floor waste, tap and mixer penetrations, and any fixing drilled into a wet wall.

The exact heights and extents depend on whether the floor is timber or concrete, whether the shower is enclosed or unenclosed, and how the room is set out. This is one of the reasons a diagram found online is not a substitute for someone who applies the standard for a living.

The parts people miss

The standard is not only about where the membrane goes. It also deals with:

Falls to the waste. Water has to actually leave the room. A floor that ponds will find a way through eventually, no matter what is underneath it.

Movement joints and bond breakers. Buildings move. Timber floors move more. The standard requires details at junctions that let the membrane accommodate that movement rather than tearing at the corner.

Substrate suitability. The membrane has to be applied over something appropriate and properly prepared. Water-resistant sheeting is not the same as waterproof, and the difference matters.

Compatibility. The membrane, the primer, the tile adhesive and the substrate all have to work together. Mixing systems from different manufacturers without checking compatibility is a genuine cause of failure.

Why the detail matters more than the product

Nearly every membrane sold in Australia will do its job if it is applied correctly. Almost every failure we strip out is an application failure, not a product failure: not enough coats, insufficient cure time, corners not reinforced, penetrations not dressed.

That is worth knowing when comparing quotes. The brand of membrane matters far less than whether the person applying it will take the time the system requires. How long waterproofing takes to dry is the single most useful question to ask, because the answer tells you whether they are planning to rush it.

What you should get

Ask for the licence number of whoever does the waterproofing, and keep the documentation. Waterproofing certificates in NSW explains what you should end up with and why it matters at resale.

If you want the wet areas in your bathroom done to the standard, with the paperwork to prove it, that is what our waterproofing service covers.