AS3740 Waterproofing Standard: What Every Australian Homeowner Needs to Know Before They Renovate
Every bathroom we renovate is waterproofed to AS3740 — inspected, certified by licensed contractors, and signed off before a single tile goes down.
Waterproofing is the one part of a renovation you can’t see once it’s done. If it’s wrong, you won’t find out until there’s a leak, a failed inspection, or an insurance claim that goes nowhere. This page is for you if: you’re renovating a bathroom and want to understand what AS3740 requires, you’re vetting contractors, or you’ve just been told your waterproofing isn’t compliant and you’re trying to work out what that means.
What Is AS3740, and Why Does It Exist?
AS/NZS 3740 — the full title is Waterproofing of Domestic Wet Areas — is the Australian and New Zealand Standard that spells out how waterproofing must be applied in bathrooms, ensuites, laundries, and anywhere else water gets used in a home. It’s referenced in the National Construction Code, which makes it a legal requirement, not a suggestion. If a licensed contractor is doing the work, compliance isn’t optional.
The standard came about because water damage in wet areas has always been one of the biggest — and most expensive — defect claims in Australian residential construction. Before a defined standard existed, every tradie applied whatever they thought was enough. Some were thorough. Many weren’t. The results were predictably inconsistent and the costs of fixing them were predictably high.
Which Areas Does AS3740 Cover?
AS3740 applies to any area in a home that receives water — either intentionally or as a byproduct of normal use. For a bathroom renovation, that generally means:
Worth knowing: Even if you're only retiling a shower and not doing a full bathroom renovation, AS3740 still applies the moment any existing membrane gets disturbed — even a small section. Some contractors are good about flagging this. Others aren't.
The document that sets out exactly how waterproofing must be applied in bathrooms, ensuites, laundries, and all other domestic wet areas. Referenced directly in the National Construction Code. If a licensed contractor is doing your renovation, this applies.
AS3740 sits within the NCC, which means compliance isn't advisory — it's a legal requirement on any licensed renovation or new residential build. The NCC sets the building performance requirements; AS3740 sets the technical method for meeting them in wet areas.
Waterproofing is the one part of a bathroom renovation you can't see once it's done. The tiles go down, everything looks great, and whatever was done underneath is locked in — for better or worse — for the next decade or two.
What AS3740 Actually Requires
People often assume compliance is about which product you use. It’s not — or at least, not primarily. AS3740 sets minimum requirements for how and where the membrane goes, and what has to happen before tiling can start. Here’s what that looks like in practice.
| Requirement | What it means in practice |
|---|---|
| Membrane height (shower walls) | Minimum 1,800mm from the shower base up the shower walls. In practice, most compliant jobs take the membrane to the full tiled height — the 1,800mm is the floor, not the target. |
| Coverage zones around baths | Minimum 150mm horizontal extension from the top of a bath or shower base, and 150mm up adjacent walls. At the floor-to-wall junction, a minimum 50mm upstand is required. |
| Membrane type & thickness | The standard recognises sheet membranes, liquid-applied systems, and pre-formed bases. Each must be applied to the manufacturer’s specifications. Liquid-applied systems require a minimum of two coats to achieve the required dry film thickness. |
| Floor falls to drainage | Minimum 1:80 fall to the waste, with 1:60 the practical standard on most jobs. Inadequate floor falls cause pooling, which accelerates membrane failure and grout breakdown over time. |
| Bond breakers at junctions | Flexible movement joints at all internal corners and floor-to-wall junctions, installed before any membrane is applied. Buildings move. Bond breakers let the membrane accommodate that movement without cracking. Skipping them is the most common shortcut on underpriced jobs. |
| Penetration sealing | Every penetration through the floor or walls — pipes, waste outlets, fixings — must be individually sealed before membrane application. These are the points where water finds a way through if the prep work isn’t done properly. |
Who Has to Comply — and When?
There’s a persistent myth that AS3740 only applies to new builds. It doesn’t. Any renovation where waterproofing work is carried out — or where existing waterproofing is disturbed — triggers compliance requirements.
Compliance is mandatory. A licensed waterproofer must complete and certify the work before tiling begins. No exceptions.
If the membrane is intact and untouched, you may not need to re-waterproof. But the moment any membrane is disturbed — even a small section — that area must come up to current standard before the new tiles go on.
Water running through your bathroom floor into the unit below becomes a neighbour dispute and a strata claim. Some schemes have internal requirements that go beyond the base AS3740 standard. Check with your strata manager before starting work.
AS3740 compliance is mandatory on all new residential construction. Applies regardless of whether the builder is large or small, registered or a sole trader.
The waterproofing work must be done by a licensed contractor. In most states, that means a licensed builder, a licensed waterproofer, or a licensed tiler with a waterproofing endorsement. It varies by state. Ask for the licence number before anyone starts work.
⚠ Unlicensed waterproofing voids your insurance. If water damage occurs and your insurer asks to see the contractor’s licence and compliance certificate — and you can’t produce either — you’re footing the full repair bill yourself. This is not a hypothetical. It happens.
What Actually Happens When Waterproofing Fails
Non-compliant waterproofing rarely fails on day one. That’s the frustrating thing. The problem builds quietly and invisibly for months, sometimes years, and then presents as a major repair job with no warning. Here’s what that looks like when it finally surfaces.
Persistent moisture in a subfloor or wall cavity causes timber to rot and metal fixings to corrode. By the time you can see it or smell it, the repair isn’t just replacing the waterproofing — it’s replacing structural elements. We’ve seen bathroom renos that cost $15,000 turn into $40,000+ repair jobs because nobody put a proper membrane in.
Pre-sale building reports flag waterproofing defects. If the inspection finds non-compliant work, you’ll either need to rectify it before settlement — under time pressure, at whatever price the market charges when you have no leverage — or renegotiate the sale price to account for it.
Insurers ask for waterproofing certificates. If the work wasn’t done by a licensed contractor, or if there’s no certificate, water damage claims routinely get denied. The coverage you’ve been paying for doesn’t protect you if the underlying work wasn’t compliant.
Moisture trapped behind tiles creates conditions where mould thrives — hidden, unventilated, feeding off timber or plasterboard. It doesn’t always smell. Sometimes the first sign is discolouration at the grout lines, by which point the problem behind the wall is already significant.
Water doesn’t care about property boundaries. If it travels through your bathroom floor into the unit below, the owners there will have a legitimate claim against you. Depending on the extent of damage, this can get expensive quickly — and it all traces back to what was (or wasn’t) done under those tiles.
What a Properly Done Waterproofing Job Actually Looks Like
Most homeowners have never watched a waterproofing job being done. It’s not the most photogenic part of a renovation. But if you know what to look for, it’s not hard to tell whether a job is being done properly. Here’s the sequence on a compliant job.
The concrete slab, fibre cement sheet, or compressed sheet substrate is cleaned, dried, and checked for structural soundness. Every penetration — pipes, waste outlets, fixings — is sealed individually. This step happens before any membrane goes on and is never visible once tiling is complete.
Flexible movement joints go in at every internal corner and floor-to-wall junction. Buildings move. These bond breakers let the membrane accommodate that movement without cracking. If your contractor wants to skip this step, that’s a red flag worth noting before you let them proceed.
Liquid-applied membrane goes on in the first coat, covering the full shower floor, up the walls to the required height, and lapping over all junctions and upstands. Coverage rate is checked against the product data sheet.
The first coat must fully cure before the second coat goes on. Minimum 24 hours in normal conditions, longer in cold or high humidity. Same-day second coat application is not compliant and not something we do.
The second coat brings the membrane to the required dry film thickness. Before tiling starts, the waterproofing is inspected — coverage at junctions, membrane height, no tiling over fresh membrane. This inspection hold point is what separates a properly run job from a rushed one.
On completion, you receive a waterproofing compliance certificate: signed, dated, with the contractor’s licence number and the membrane system used. Keep this document. You will need it if you ever sell, refinance, or make a water damage claim.
The certificate matters: A waterproofing compliance certificate records the membrane system used, areas covered, and the contractor’s licence details. If you sell, refinance, or make a claim, someone will ask for it. File it with your building documents from day one.
How to Verify Compliance — Questions Worth Asking
You don’t need to be a waterproofing expert to protect yourself. You just need to ask a few direct questions before any work starts — and pay attention to how they get answered. A contractor who knows their work will answer without hesitating. One who hedges is telling you something.
- Are you a licensed waterproofer — or does your team include one? Ask to see the licence number.
- What membrane system are you using, and what’s the required dry film thickness?
- Will I receive a waterproofing compliance certificate on completion?
- Who is responsible for the inspection before tiling begins?
- Check that tiling doesn’t start the same day as waterproofing — membrane needs to cure.
- Ask to see the product data sheet to confirm the coverage rate being applied.
- Look at the floor-wall junction before tiling: a bond breaker should be visible at every internal corner.
- Get the compliance certificate in writing — not a verbal assurance. A signed document with a licence number.
- File the contractor’s licence number and membrane product name with your building records.
Red Flags When Hiring a Contractor
Most of the shortcuts in waterproofing are invisible once the job is done — but several of them show up in how a contractor talks about the work before it starts. Here’s what to watch for.
Liquid membrane needs 24–48 hours minimum to cure. Same-day tiling over a fresh membrane is a compliance failure. The only exception is a documented fast-cure system — and they should be able to name the product.
That means they’re applying whatever’s cheapest and available, not specifying a system to meet AS3740. A waterproofer who knows their trade will name the product, the brand, and the dry film thickness requirement without pausing.
Ask for it explicitly. If they hedge or say ‘that’s not really standard around here’ — that tells you a lot about how they work. The certificate isn’t optional; it’s part of what a compliant job includes.
Low waterproofing quotes almost always reflect shortcuts somewhere — thinner coats, fewer coats, skipped bond breakers, no inspection. There’s no magic that makes compliant waterproofing cheap. The materials alone have a floor price.
Ask for it before you sign anything. A licensed contractor won’t blink at the question. Someone who hesitates or deflects when you raise it — that’s already a red flag you shouldn’t ignore.
Most liquid-applied systems require a minimum of two coats. If you see the first coat go on and the tiler start shortly after, ask what’s happening. One thin coat over the required coverage is not compliant regardless of which product was used.
Related reading: Our Building Codes & Compliance page covers the broader regulatory framework — permits, waterproofing standards, and trade licensing requirements for any bathroom renovation.
Questions We Get Asked a Lot
Yes — and not just for new builds. Any renovation that disturbs existing waterproofing, installs a new shower, or retiles over bare substrate needs to comply with AS3740. It’s a legal requirement under the National Construction Code, and the contractor doing the work is obligated to certify it. If they’re not offering to certify, ask why.
The standard sets a minimum of 1,800mm up from the shower base on shower walls. Most jobs worth doing go higher than that — taking the membrane to the full tiled height leaves no exposed surface for water to find. The 1,800mm is the minimum floor, not the target you’re aiming for.
It’s a signed document from the licensed contractor confirming the waterproofing was completed to AS3740 requirements. You need it for insurance claims, for resale, and for strata compliance. If your contractor isn’t offering one, ask for it specifically before work starts — not after. If they can’t produce one, that’s worth understanding before you hand over a deposit.
In most states, waterproofing in a bathroom must be performed by a licensed contractor if it’s going to be certifiable. You can buy compliant products and apply them yourself, but you won’t be able to get it certified, your insurer won’t accept it for a water damage claim, and it’ll create problems when you sell the property. The cost of getting it done properly is a lot lower than the cost of dealing with an uncertified job later.
Same document. The AS/NZS designation just means it’s adopted jointly by Australia and New Zealand. You’ll see both references used — sometimes in the same quote or specification — and they mean the same thing.
For most liquid-applied systems, you’re looking at 24 to 48 hours between coats, and again before tiling starts. Temperature and humidity affect that — cold, damp weather slows cure time significantly. Any contractor scheduling tiling on the same day as waterproofing is either working with a documented fast-cure product or they’re not letting it cure at all. Ask which one it is.
It depends on what’s underneath. Suspended timber subfloors generally require full-floor waterproofing. Concrete slab construction may only require the shower zone under the base AS3740 requirements — though a lot of builders extend it to the full floor regardless, because it’s cheap insurance compared to the cost of fixing a leak later. Your contractor should be able to tell you which applies to your bathroom and why.
Pre-sale building inspections catch waterproofing defects. If yours comes back non-compliant, you’re looking at either completing rectification works before settlement — under time pressure, at whatever it costs — or renegotiating the sale price to account for the defect. Neither is a good position to be in. Getting it right the first time is significantly cheaper than dealing with it when you’re trying to sell.