AS 3740 Waterproofing and Certificates in Victoria

Why waterproofing is the most important part of your bathroom

When you walk into a newly renovated bathroom, you see tiles, tapware, glass and joinery. What you do not see is the waterproofing system beneath the tiles, yet it is the part that determines whether the bathroom lasts. Grout and tiles are not waterproof. Water passes through grout lines and around fixtures every time the shower runs. The membrane beneath is what stops that water reaching the timber frame, floor structure and adjoining rooms.

When waterproofing fails, the damage is usually hidden for months or years. Signs include loose or drummy tiles, mould on skirting boards outside the bathroom, swelling architraves, bubbling paint, a musty smell, and on upstairs bathrooms, stains on the ceiling below. By the time these appear, the damage may extend to the structure and the only proper fix is to rebuild the bathroom.

This guide explains the Australian Standard that governs wet-area waterproofing, what compliant work involves and what documentation you should expect in Victoria.

What is AS 3740?

AS 3740, Waterproofing of domestic wet areas, is the Australian Standard that sets out minimum requirements for materials, design and installation of waterproofing in domestic bathrooms, laundries, toilets and similar wet areas. It is referenced by the National Construction Code, which is adopted in Victoria through the building regulations. The current edition was updated in 2021 and introduced clearer requirements around wet-area zones and shower design.

In practical terms, AS 3740 tells builders and waterproofers:

• Which parts of a wet area must be waterproof and which must be water-resistant.
• The minimum heights and extents of membranes.
• How to treat junctions between walls and floors.
• How to detail floor wastes, penetrations and hobs.
• The required falls on floors.
• Which materials are suitable.

The standard sets a minimum. Many quality builders exceed it, for example by waterproofing the entire bathroom floor when only part is strictly required.

Understanding wet-area zones

AS 3740 divides a bathroom into areas based on how much water they are likely to receive.

The shower area

The area around the shower outlet receives the most water and must be waterproof on the floor and walls to specified heights. The extent of the shower area depends on whether the shower has a screen, a hob, a step-down or none of these. An unenclosed shower, such as a walk-in shower with only a partial panel, generally requires a larger waterproofed area because water can spread further.

Areas outside the shower

The remainder of the bathroom floor must be at least water-resistant, and in many cases waterproof, depending on the design and the floor material. Timber floors and particleboard are more vulnerable than concrete, so treatment requirements differ. Wall-floor junctions throughout the room need specific treatment.

Baths and spas

Walls adjoining baths need waterproofing above the bath to a set height, and the junction between bath and wall must be properly detailed. Inserted baths have requirements for the area beneath and around the bath.

Vanities and basins

Walls behind basins and taps need protection where splashing is expected, and penetrations must be sealed.

Laundries and toilets

Laundry floors and walls behind troughs and machines also have requirements, and floors in separate toilets typically need water-resistant treatment at the junctions.

Key elements of compliant waterproofing

Substrate preparation

Before any membrane is applied, surfaces must be clean, dry, sound and suitable for the chosen product. Sheet joints should be set, and screeds must be cured. Timber floors must be stiff and fitted with an appropriate underlay.

Falls

Floors in shower areas must fall to the floor waste so water drains away without pooling. The required fall depends on the area and design. Falls are created in the substrate or screed beneath the membrane, not just in the tile bed, so that water reaching the membrane also drains.

Bond breakers

At internal corners, such as where walls meet floors, a bond breaker is installed so the membrane can stretch slightly as the building moves without tearing. This might be a tape, a sealant bead or a purpose-made angle depending on the system. Missing bond breakers are a common cause of failure.

Puddle flanges

A puddle flange is fitted around the floor waste so the membrane can be turned down into it. This ensures water that passes through the tiles and reaches the membrane can still escape down the drain.

Penetrations

Pipes and fixtures that pass through the membrane, such as mixer bodies and shower arms, must be sealed with collars or flanges compatible with the membrane.

Membrane thickness and curing

Liquid membranes must be applied at the manufacturer’s specified thickness, often in two or more coats, and allowed to cure fully. Sheet membranes have their own installation requirements. Curing time varies with temperature and humidity.

Water stops and hobs

Where the shower floor meets the rest of the bathroom, a water stop angle or hob may be used to stop water travelling under the tiles. The membrane is dressed onto it. Level-entry showers need especially careful detailing.

Compatibility

Membranes, primers, adhesives and sealants must be compatible with each other. Using a system from one manufacturer reduces the risk of incompatibility.

Who can carry out waterproofing in Victoria?

In Victoria, domestic building work, including bathroom renovations above a set value, must be carried out under a registered domestic builder. Waterproofing itself is commonly done by specialist applicators trained in the product they are installing, working under the builder’s supervision. Plumbing work associated with the bathroom must be carried out by a licensed plumber, who issues a compliance certificate for that work. Electrical work must be carried out by a licensed electrician, who issues a certificate of electrical safety.

Ask your builder who will apply the membrane, which product they will use and what training or accreditation the applicator holds.

What is a waterproofing certificate?

A waterproofing certificate is a document provided by the waterproofing applicator or builder confirming that the membrane was installed in accordance with AS 3740 and the manufacturer’s instructions. It usually includes:

• The property address and the room or rooms treated.
• The date of installation.
• The membrane system and products used.
• A statement of compliance with AS 3740.
• The applicator’s details.
• Warranty information for the membrane and workmanship.

Some applicators also provide photographs of each stage, which are excellent evidence of what was done.

Why the certificate matters

Peace of mind

The certificate confirms the work was done to the standard. Combined with photographs, it gives you confidence that the hidden part of your bathroom was built correctly.

Warranty claims

If a problem arises, the certificate and photographs support a warranty claim and help identify responsibility.

Selling your home

Buyers and their inspectors may ask about the age and quality of bathrooms. A waterproofing certificate, along with plumbing and electrical certificates, adds credibility.

Insurance

In the event of water damage, documentation showing compliant installation may assist when dealing with your insurer.

Inspections and testing

Good practice includes inspecting the membrane before tiling and, in some cases, flood testing the shower or floor to confirm it holds water. Ask your builder whether they flood test and whether you can see the membrane before tiles go down. Photographs are taken at each stage so there is a record even after tiling.

Signs your existing waterproofing has failed

• Loose, cracked or drummy tiles in or near the shower.
• Grout that crumbles or keeps going mouldy.
• Silicone that keeps failing.
• Damp or swollen skirting boards, architraves or door frames near the bathroom.
• Bubbling paint or mould on walls outside the bathroom.
• Water stains on the ceiling below an upstairs bathroom.
• A persistent musty smell.
• Soft or springy floors.

If you notice these, have the bathroom assessed promptly. Early intervention can limit damage.

Can waterproofing be repaired without removing tiles?

Some products are marketed as penetrating sealers that can be applied over tiles and grout to reduce water ingress. They may help in limited circumstances, such as slowing water through porous grout, but they are not a substitute for a compliant membrane beneath the tiles. Regrouting and resealing can address surface issues, but if the membrane itself has failed, the only reliable fix is to remove the tiles and install a new waterproofing system.

Waterproofing in hills homes

Bathrooms on timber floors, common in Upper Beaconsfield, Emerald, Cockatoo and Gembrook, need particular care. Timber moves with moisture and temperature, so floors must be stiff, the substrate compatible and bond breakers correctly installed. Cooler, damper weather can lengthen curing times. Older hills homes are also more likely to have hidden water damage from previous failures, which must be repaired before new waterproofing goes down.

Liquid versus sheet membranes

Most domestic bathrooms in Victoria use liquid-applied membranes, which are brushed or rolled on in multiple coats. They conform easily to corners, penetrations and complex shapes, but their performance depends on achieving the right thickness and full cure. Sheet membranes arrive at a consistent thickness from the factory and can be tiled sooner, but every seam and corner must be lapped and sealed correctly. Some systems combine both, using sheet material in the shower and a liquid elsewhere. Each approach can comply with AS 3740 when installed properly; what matters most is the skill and care of the applicator and the use of a complete, compatible system.

Keeping records with your home documents

Store your waterproofing certificate and photographs with your other important property documents, ideally in both paper and digital form. If you renovate further, sell, or need to make a claim, having the records at hand saves time.

Questions to ask your builder

• Which waterproofing system will you use?
• Who will apply it, and what is their experience with the product?
• Will the whole floor be waterproofed or only the shower area?
• How will level-entry or hobless showers be detailed?
• Will you flood test before tiling?
• Will I receive photographs and a certificate?
• What warranty applies to the membrane and workmanship?

Our waterproofing standard

At Beaconsfield Bathroom Renovations, every bathroom we build is waterproofed in accordance with AS 3740 using a complete, compatible system. We install bond breakers, puddle flanges and sealed penetrations, apply membranes at the specified thickness and allow full curing time before tiling. Each stage is photographed, and you receive a waterproofing certificate along with plumbing and electrical certificates at handover. We often exceed the minimum requirements, because the cost of doing it properly is small compared to the cost of failure.

Summary

Key takeaways: AS 3740 governs where membranes go and how junctions are treated, cure times matter, and the certificate belongs in your property records. The short version: a well-planned bathroom starts with an honest assessment, a clear written scope and waterproofing to AS 3740, and it is finished by licensed and insured trades who take the time to get details right. Use this guide to prepare questions for your consultation, and bring photos, measurements and any concerns about water damage. The more we understand about your home and how you use the room, the better the advice we can give.

Book a design consultation

If you are planning a bathroom renovation or suspect your current bathroom is leaking, book a design consultation. We will assess the room and explain exactly how we would waterproof it to last.

Our bathroom services

• Accessible Bathrooms
• Bathroom Renovations
• Bathroom Resealing & Silicone
• Bathroom Tiling
• Ensuite Renovations
• Laundry Renovations
• Shower Conversions
• Shower Screens
• Small Bathroom Renovations
• Tile & Grout Cleaning
• Vanity Replacement
• Bathroom Waterproofing