AS 3740:2021 is the Australian Standard that sets out how wet areas in homes — including your shower and bathroom — must be waterproofed. It defines where waterproofing has to go, how high it must reach, and how it should be installed so the room stays watertight for the long term. If your shower leaks, there’s a good chance it was never built to this standard in the first place. Here’s what AS 3740 actually requires, in plain English.

Not sure your shower was waterproofed to standard? Book an inspection and we’ll check whether it meets AS 3740 — and what to do if it doesn’t.

What is AS 3740?

AS 3740 — “Waterproofing of domestic wet areas” — is the national standard that governs how bathrooms, showers, laundries and other wet areas are waterproofed in Australian homes. It exists because failed waterproofing is one of the most common and most expensive building defects in the country. When a builder or waterproofer follows AS 3740, your shower gets a properly installed membrane that keeps water off the structure of your home. When they cut corners, the shower leaks — often within a few years.

The current version is AS 3740:2021, which updated the previous 2010 edition. It’s referenced by the National Construction Code, which means compliance isn’t optional — it’s the benchmark any compliant wet area is built to.

Where does AS 3740 require waterproofing?

The standard sets different requirements for different parts of the room, based on how much water each area is exposed to. In broad terms, it requires waterproofing of:

  • The shower floor, in full.
  • The shower walls to a set height above the floor.
  • All wall and floor junctions and the corners where walls meet — the joints where leaks most often start.
  • Around the drain, taps and any penetrations through the wall or floor.
  • The bathroom floor more broadly, with the extent depending on the room’s construction (for example, timber floors and the areas around the shower need more coverage).

The detail is what matters. A membrane that stops short of a required height, skips a corner, or isn’t properly bonded around the drain will leak no matter how good the tiling looks on top.

What changed in the 2021 update?

AS 3740:2021 refined and clarified the earlier edition rather than reinventing it. The updates tightened the requirements around things like the waterproofing of junctions and penetrations, the treatment of different substrates, and the detailing that makes a membrane actually perform. For a homeowner, the takeaway is simple: the standard has become more rigorous about the details that cause real-world leaks, so an older or poorly built shower is even more likely to fall short of what’s expected today.

How waterproofing is meant to be done

Under the standard, waterproofing isn’t just a coat of product — it’s a system. The substrate has to be sound and prepared, the membrane applied to the right thickness and heights, junctions and penetrations detailed correctly, and the membrane given time to cure before tiling. Skipping the curing time, tiling over a membrane that’s too thin, or missing the junctions are all common ways a shower ends up non-compliant and leaking. (For the bigger picture on how the membrane works and fails, see our shower waterproofing guide.)

How to tell if your shower was done to standard

You can’t see the membrane, so you judge it by the symptoms of failure:

  • Water stains on the ceiling or wall below or beside the shower.
  • Mould that keeps returning no matter how often you clean it.
  • Loose, drummy or lifting tiles, or grout that keeps cracking.
  • A musty smell, bubbling paint, or swollen skirting outside the bathroom.

Any of these suggests water is reaching the structure — which usually means the waterproofing has either failed or was never done to AS 3740 in the first place.

What to do if your shower doesn’t meet the standard

It depends on how far the water has got. If the tiles and membrane are still sound and the problem is perished silicone or grout, a reseal restores the shower without removing tiles. If the membrane itself has failed, the shower needs to be stripped back and re-waterproofed to AS 3740:2021 — that’s a shower rebuild. Either way, the fix should bring the wet area up to the current standard so it doesn’t happen again.

AS 3740 in Brisbane and the Gold Coast

Our warm, humid climate is unforgiving on a shower that wasn’t built to standard — the seals break down faster and any weakness in the waterproofing shows up sooner. If you’re building or renovating in Brisbane or the Gold Coast, make sure the waterproofing is done to AS 3740:2021 and given time to cure before tiling. If you’ve got an older shower that’s showing the warning signs above, it’s worth having it checked.

Get your waterproofing checked against the standard

A shower that doesn’t meet AS 3740 will keep leaking until it’s put right. Book an inspection with Leaky Showers and we’ll tell you whether yours meets the standard — and how to fix it if it doesn’t.

Frequently asked questions

What is AS 3740?

AS 3740 is the Australian Standard for waterproofing domestic wet areas — showers, bathrooms, laundries and similar. It sets out where waterproofing is required, the heights it must reach, and how it must be installed. The current edition is AS 3740:2021.

Is waterproofing to AS 3740 a legal requirement?

The standard is referenced by the National Construction Code, so wet areas in Australian homes are expected to be waterproofed to it. A shower that isn’t built to the standard is effectively a building defect.

What did AS 3740:2021 change?

The 2021 edition clarified and tightened the earlier version, particularly around junctions, penetrations, substrates and the detailing that makes a membrane perform. It’s more rigorous about the details that cause real-world leaks.

How do I know if my shower meets AS 3740?

You can’t see the membrane, so you look for signs of failure: recurring mould, water stains below or beside the shower, loose or drummy tiles, cracking grout, or a musty smell. Any of these suggests the waterproofing has failed or was never done to standard. An inspection confirms it.

Can a shower be brought up to standard without a full rebuild?

If the membrane is still sound and only the silicone or grout has failed, a reseal restores it without removing tiles. If the membrane itself has failed, the shower needs to be rebuilt and re-waterproofed to AS 3740:2021.