Shower Repairs Australia
Understanding AS 3740 Waterproofing Standards for Showers
AS 3740 is the Australian Standard for waterproofing in domestic wet areas, and it applies to every bathroom renovation, new build, and shower repair in Victoria.
AS 3740 sets out exactly how waterproofing must be installed in bathrooms, laundries, and other wet areas in homes. The current version, AS 3740:2021, replaced the earlier 2010 version with updated requirements based on two decades of experience.
Water damage in Australian homes costs billions annually. Poor waterproofing leads to mould growth, rotting timber, structural damage, and health problems. In Victoria, water ingress issues consistently top the list of building complaints made to the Victorian Building Authority. Research shows up to 70% of buildings constructed since 2000 have experienced leaks, many caused by substandard waterproofing.
AS 3740 has legal force because it’s referenced in the National Construction Code, enforced through Victorian legislation including the Building Act 1993 and Building Regulations 2018. The Victorian Building Authority oversees compliance and can issue building notices requiring defective work to be fixed. Builders can be held liable for waterproofing defects for up to ten years after completion.
The 2021 update introduced several important changes. Where tiles drain to a floor waste, the waterproof membrane underneath must also be graded to drain properly. The minimum fall to waste in shower areas changed from 1:100 to 1:80. Wall waterproofing in shower areas now must extend to either 1800mm above the floor or 50mm above the shower rose, whichever is higher.
In Victoria, the Building and Plumbing Commission manages these regulations through registered building practitioners. Only registered practitioners can authorise that waterproofing work complies with the standard. Building surveyors must verify compliance before giving final approval.
Installing proper waterproofing during construction or renovation costs a fraction of what you’ll pay to fix water damage later. A leaking bathroom can cause tens of thousands of dollars in structural repairs, plus the disruption of demolition and replacement. The standard provides clear requirements so there’s no ambiguity about what properly waterproofed means.
When does AS 3740 apply to your bathroom?
AS 3740 applies whenever waterproofing work happens in a domestic wet area. This includes new bathroom construction, complete renovations, and repairs where the waterproof membrane needs replacing or modification.
For new bathroom construction, AS 3740 applies without exception. Complete bathroom renovations where you’re stripping back to the substrate have the same requirements. These situations require building permits in Victoria, and the building surveyor will specifically check waterproofing compliance before signing off.
If your renovation involves any work on the waterproofing membrane, even partial repairs or modifications, AS 3740 applies to that work. Replacing tiles in a shower typically affects the waterproof membrane underneath, triggering compliance requirements. Even without a building permit for minor work, the waterproofing standard still applies.
Ground floor bathrooms with concrete slab floors have different requirements than upper storey bathrooms or bathrooms with timber floors. If your bathroom is on a second storey or has timber flooring (including particleboard or plywood), the entire bathroom floor must be waterproofed, not just the shower area.
In strata buildings, bathroom renovations that include waterproofing work are classified as major renovations under the Strata Schemes Management Act 2015. You need special resolution approval from the owners corporation before starting work.
When does AS 3740 apply to your bathroom?
| Scenario | AS 3740 Applies? | Key Points |
|---|---|---|
| New bathroom construction | Yes, always | Full compliance required regardless of size |
| Complete bathroom renovation | Yes, always | Stripping back to substrate triggers full requirements |
| Replacing shower tiles | Yes, likely | Affects membrane, requires compliance for affected areas |
| Installing new shower screen only | No | No waterproofing work involved |
| Upper storey bathroom any work | Yes, if waterproofing affected | Entire floor must be waterproof |
| Timber floor bathroom any work | Yes, if waterproofing affected | Entire floor must be waterproof |
Even when a building permit isn’t required, AS 3740 sets the standard for quality work. A builder who doesn’t meet the standard is doing defective work, and remains liable if problems emerge later.
Key waterproofing requirements explained simply
Shower zone requirements
All shower walls must be waterproofed to a minimum height of 1800mm above the floor substrate. If your shower rose is particularly high, the waterproofing must extend at least 50mm above it, whichever measurement is greater.
The shower floor requires complete waterproofing coverage, including any hob or step-down at the shower entrance. The waterproof membrane must be continuous with no gaps or breaks.
Unenclosed shower requirements
For unenclosed showers (showers without a full screen or door), the waterproofed floor area must cover a horizontal radius of at least 1500mm from where the shower rose connects to the wall. At this 1500mm point, a waterstop must be installed. A waterstop is a physical barrier that prevents water from flowing beyond the waterproofed area.
Junctions and penetrations
All junctions where walls meet floors in the shower area must be waterproofed, with the membrane continuing seamlessly from floor to wall. Internal corners where two walls meet need at least 40mm of waterproofing on both sides of the junction.
Penetrations through waterproofed surfaces need sealing. This includes tap connections, shower roses, mixer valve spindles, and recessed soap holders or niches.
Falls and drainage
In shower areas, the minimum fall is 1:80, meaning the floor drops at least one unit for every 80 units of horizontal distance. Over one metre the floor must drop about 12.5mm. This prevents water from pooling and finding ways through tiny imperfections in the waterproofing.
Outside the shower area
Bathroom walls outside the shower need to be water resistant to a height of 150mm above the floor. Water resistant means the wall can handle moisture and occasional splashing without damage.
For bathrooms with timber floors or bathrooms on upper storeys, the entire bathroom floor must be waterproofed, not just the shower area. This prevents damage to rooms below if water escapes the shower.
Waterproofing requirements
| Bathroom Area | Floor Requirement | Wall Requirement | Special Notes |
|---|---|---|---|
| Inside shower (enclosed) | Fully waterproof | Waterproof to 1800mm minimum | Includes all junctions and penetrations |
| Inside shower (unenclosed) | Waterproof to 1500mm radius | Waterproof to 1800mm minimum | Waterstop required at perimeter |
| Bathroom floor (concrete, ground level) | Water resistant | Water resistant to 150mm | Unless shower is unenclosed |
| Bathroom floor (timber or upper storey) | Fully waterproof | Water resistant to 150mm | Entire floor must be waterproof |
Understanding waterproofing membranes
The waterproof membrane is the invisible barrier protecting your bathroom structure from water. A waterproofing membrane is a flexible, impermeable layer applied either as a liquid that cures into a seamless coating, or as pre-formed sheets. Liquid membranes are more common in residential bathrooms.
Quality membranes must comply with AS/NZS 4858:2004, which classifies membranes based on their elastic properties. The membrane’s ability to stretch and accommodate slight building movement without cracking keeps water out over years of use.
Multiple thin coats perform better than a single thick coat. When membrane is applied too thickly at once, the surface cures faster than the layers underneath, creating pinholes as the membrane finishes curing. Professional applicators apply several thin coats with adequate drying time between coats.
Curing time between coats and before tiling varies by product and conditions. Rushing this stage causes failures. Contractors who promise unusually fast completion might be cutting corners on curing time.
The substrate must be clean, dry, structurally sound, and at the right moisture level. Excessive moisture prevents the membrane from curing properly. Professional contractors measure substrate moisture content before applying membrane.
Visual inspection before tiling provides the last opportunity to verify the membrane is properly installed. Once tiles are installed, inspecting the membrane becomes impossible without destructive testing.
How to verify your bathroom will be compliant
Verify your contractor’s credentials before work starts. In Victoria, waterproofing work must be carried out or supervised by a registered building practitioner. Check registration status on the Victorian Building Authority website.
The Certificate of Compliance is your proof that waterproofing meets AS 3740. Only licensed or registered practitioners can issue this certificate. If a contractor can’t or won’t provide one, they either aren’t qualified or aren’t planning to do the work properly.
The most important inspection happens after the waterproof membrane is applied but before tiles are installed. At this pre-tile inspection, you or an independent building inspector can visually verify the membrane covers all required areas and shows no obvious defects.
Documentation you should request includes plans showing waterproofing extent, membrane product specifications and data sheets, compatibility statements if multiple products are used, and the Certificate of Compliance upon completion.
Bathroom compliance
| Inspection Stage | What to Check | Who Can Check | Documentation |
|---|---|---|---|
| Before work starts | Contractor credentials, product specifications | Homeowner, building inspector | Registration certificate, product data sheets |
| Substrate preparation | Surface cleanliness, structural soundness, moisture levels | Homeowner, contractor, surveyor | Moisture readings if applicable |
| After membrane application (before tiles) | Complete coverage, thickness, junctions, penetrations, no pinholes | Homeowner, building inspector, surveyor | Visual inspection record, photos |
| Final completion | Overall quality, proper drainage, no defects visible | Homeowner, building inspector, surveyor | Certificate of Compliance |
Taking photos at each stage creates your own record of compliance. Photos of the waterproof membrane before tiling provide evidence of proper installation. If you’re uncertain about compliance, engaging an independent building inspector provides professional verification.
Questions to ask contractors before hiring
Licensing and credentials
Ask for their Victorian Building Authority registration number and verify it online. Request proof of current public liability insurance and professional indemnity insurance.
AS 3740 knowledge
Ask what version of AS 3740 they work to. The answer should be 2021. Ask what changed between the 2010 and 2021 versions. A knowledgeable contractor can explain the key changes.
Membrane specifications
Ask what type of membrane they use. What class is it under AS/NZS 4858:2004? How do they ensure compatibility between membrane, adhesive, and sealants?
Substrate preparation
How do they prepare the substrate before applying membrane? Do they measure substrate moisture levels? What moisture level is acceptable?
Curing and application
Ask how long they leave between membrane coats. How long between the final coat and tiling? What factors affect curing time? Be wary of contractors promising very fast completion.
Certification and warranty
Who will issue the Certificate of Compliance? When will you receive it? What warranty do they offer on their waterproofing work?
Key indicators of expertise include specific product names rather than vague descriptions, detailed explanations without prompting, willingness to provide documentation upfront, references to AS 3740:2021 specifically, and understanding of when waterstops are required.
Warning signs include vague answers to technical questions, inability to explain 2021 updates, no mention of substrate preparation or moisture testing, promises to complete work unusually quickly, reluctance to provide registration details, and significantly cheaper quotes than all competitors.
Trust your instincts. A professional contractor welcomes questions and demonstrates knowledge through specific details. Contractors who avoid questions or pressure you to decide quickly might not be the right choice.
What proper waterproofing costs in Melbourne
The average cost for waterproofing a standard bathroom in Melbourne ranges from $500 to $750 based on 2024-2025 data. This typically includes both materials and labour for membrane application on a straightforward, average-sized bathroom. However, actual costs vary significantly based on multiple factors.
The cost range extends from around $400 at the low end to $4,000 or more at the high end. Per square metre pricing typically ranges from $40 to $100.
Size affects cost obviously. Upper storey bathrooms require complete floor waterproofing, not just the shower area, immediately increasing the waterproofed area. Ground floor bathrooms with concrete slabs generally cost less.
Existing damage increases costs because remediation must happen before waterproofing. Premium waterproofing membranes cost more than basic products but offer better elasticity and longer warranties.
In Victoria, registered building practitioners typically charge more than unregistered contractors, but that includes their qualifications, insurance, and ability to issue Certificates of Compliance. Emergency services or urgent work commands 25-50% premium pricing.
Costs of waterproofing
| Cost Factor | Low End | High End | Notes |
|---|---|---|---|
| Standard bathroom, ground floor, concrete | $500 | $750 | Average scenario |
| Small ensuite, simple layout | $400 | $600 | Minimum complexity |
| Large bathroom, timber floor/upper storey | $1,000 | $2,000 | Complete floor waterproofing needed |
| Existing damage repairs | $200 | $2,000+ | Depends on extent of damage |
| Emergency/urgent service | +25% | +50% | Weekend or holiday work |
When comparing quotes, ensure you’re comparing equivalent scope. A quote including substrate preparation, premium membrane, adequate curing time, and Certificate of Compliance costs more than basic membrane application without proper preparation.
Be particularly wary of quotes significantly below the market average. Waterproofing that costs half what everyone else quotes either uses inferior materials, skips critical steps, rushes application, or comes from unqualified contractors.
Consequences of non-compliant waterproofing
Immediate impacts
Failed inspections stop your renovation. If waterproofing doesn’t meet AS 3740 requirements, building surveyors can refuse to sign off. You can’t proceed to tiling and finishing until waterproofing compliance is verified.
Mandatory rework often means removing newly installed tiles, stripping back to substrate, and starting waterproofing again properly. Rework easily costs double or triple what proper waterproofing would have cost initially.
Legal consequences
The Victorian Building Authority can issue building notices requiring defective work to be rectified. These notices have legal force and set timeframes for fixing problems. Builders remain liable for defective waterproofing for up to ten years from completion under Victorian legislation.
Financial and property impacts
Property value impacts occur when waterproofing problems are discovered during pre-sale building inspections. Identified waterproofing issues can reduce your property value by thousands or cause buyers to walk away.
Structural damage from failed waterproofing extends far beyond the bathroom. Water penetrating through failed waterproofing rots timber framing, causes concrete cancer, damages electrical systems, and creates mould problems affecting air quality throughout the home.
Health and safety
When waterproofing fails and water enters wall and ceiling cavities, mould develops in hidden spaces. Mould spores can cause respiratory problems, allergic reactions, and other health issues, particularly for children, elderly people, and those with existing respiratory conditions.
Victorian statistics show water damage consistently tops complaint lists. Research by the Building and Plumbing Commission found water ingress and moisture damage routinely lead complaints, claims, and disputes. Waterproofing defects affect 23% of recently surveyed strata buildings.
Proper waterproofing during initial construction or renovation costs $500-750 for an average bathroom. Fixing failed waterproofing after tiles are installed costs several thousand dollars for demolition and replacement. If the failed waterproofing caused structural damage, repairs can reach $20,000-50,000 or more.
Insurance implications of waterproofing compliance
Standard home insurance policies cover sudden, accidental water damage from events like burst pipes or storm damage. However, most policies specifically exclude preventative measures. Your home insurance won’t pay for waterproofing itself because that’s routine maintenance and risk prevention.
If you make an insurance claim for water damage and the insurer discovers that waterproofing doesn’t meet AS 3740, they may reject your claim on grounds that the damage resulted from unapproved building work or lack of proper maintenance.
When waterproofing fails due to poor installation, the responsible party is the contractor who did defective work, not your home insurer. Your recourse is against the builder or waterproofing contractor.
The catch-22 situation: The insurer rejects the claim saying waterproofing was defective. Meanwhile, the builder’s warranty period has expired or the builder can’t be located. Domestic Building Insurance might cover the situation if the builder has died, become insolvent, or disappeared, but only for contracts over $16,000 where DBI was properly arranged.
Domestic Building Insurance is mandatory for domestic building contracts over $16,000 in Victoria. It covers costs up to $300,000 to fix structural defects for six years and non-structural defects for two years. However, claims can only be made if the builder dies, goes bankrupt, cannot be found, or fails to comply with tribunal or court orders.
Keep every certificate, compliance statement, invoice, contract, and piece of correspondence related to your bathroom waterproofing. Photograph the waterproof membrane before tiling. If you ever need to make an insurance claim or pursue the contractor for defective work, this documentation provides evidence.
Insurance
| Situation | Home Insurance Coverage | Builder Liability | Your Position |
|---|---|---|---|
| Sudden pipe burst causes water damage | Likely covered | Not applicable | Claim on home insurance |
| Gradual leak from poor waterproofing | Likely not covered | Builder responsible if within warranty period | Pursue builder or DBI if applicable |
| Storm water enters through inadequate seals | May be covered depending on policy | Builder responsible if work recent | Check both insurance and builder warranty |
| Need preventative waterproofing for renovation | Not covered | Not applicable | Pay from renovation budget |
| Failed waterproofing, builder disappeared | Not covered by home insurance | May be covered by DBI if contract was over $16k | Claim on DBI if available |
Compliant waterproofing protects you from needing insurance claims in the first place. Money spent on proper AS 3740 compliant waterproofing prevents expensive damage and insurance complications.
Red flags that indicate a problem
Contractor credentials and pricing
Any contractor who can’t immediately provide their Victorian Building Authority registration number should be avoided. Reluctance to provide proof of insurance suggests the contractor isn’t properly insured or isn’t legitimate.
If most quotes for your bathroom waterproofing range from $600-800 but one quote comes in at $350, question why. The cheap quote contractor is either cutting corners, lacking proper qualifications, or doesn’t understand the full scope.
Process and knowledge
Contractors suggesting skipping inspections or discouraging your involvement raise concerns. Quality contractors welcome inspections because they’re confident their work meets standards.
Contractors seeming unfamiliar with AS 3740:2021 updates or unable to explain requirements indicate gaps in knowledge. Inability to explain where waterstops go or why certain areas need waterproofing suggests insufficient expertise.
Materials and application
Contractors should specify exactly what membrane brand and type they’ll use, whether it complies with AS/NZS 4858:2004, and what class it is. Responses like industry standard membrane aren’t specific enough.
If a contractor promises to waterproof and tile a bathroom in two days, they’re planning to rush curing times. Proper membrane application requires multiple coats with drying time between coats, then adequate curing before tiling.
Documentation and installation
Any contractor who says certificates aren’t necessary or promises we’ll sort that out later is either unqualified to issue certificates or doesn’t plan to provide them.
Watch for contractors who don’t clean surfaces thoroughly, don’t check for damage, or don’t mention moisture testing. Application problems include applying membrane in single thick coats rather than multiple thin coats, insufficient attention to corners and junctions, and waterstops missing or installed incorrectly.
Post-work problems that suggest waterproofing failures include mould appearing quickly after completion, tiles becoming loose or lifting, water pooling in shower rather than draining, and discolouration appearing on walls or ceilings near the bathroom.
Trust your instincts. If something feels wrong, investigate further. Better to ask too many questions than proceed with a contractor you’re uncomfortable with and end up with failed waterproofing.
Professional contractors welcome questions because they understand informed clients make better decisions and appreciate quality work. Contractors who discourage questions are prioritising their convenience over your interests.
Taking action with confidence
Get multiple quotes from different contractors. Aim for at least three quotes so you understand the market rate and can compare approaches. Request breakdowns showing materials, labour, and timeline separately.
Check credentials thoroughly. Verify Victorian Building Authority registration, confirm insurance coverage, check online reviews, request references from similar recent projects, and verify they can issue Certificates of Compliance.
Ask questions without worrying about seeming too inquisitive. Professional contractors expect informed clients to ask detailed questions. Take notes during discussions so you can compare answers across contractors.
Document everything from initial quotes through project completion. Keep digital and physical copies of all contracts, quotes, product specifications, certificates, invoices, and correspondence. Take photos at every stage, particularly of the waterproof membrane before tiling.
Attend inspections whenever possible, particularly the pre-tile inspection where waterproof membrane is visible. Don’t rush decisions based on pressure or convenience. Quality contractors understand that homeowners need time to make informed decisions.
Insist on compliance without apology. AS 3740 compliance isn’t optional or negotiable. Contractors may suggest shortcuts or variations that work just as well but don’t meet the standard. Decline these suggestions firmly.
Keep records permanently and accessibly. Your waterproofing documentation may be needed when selling your property, making insurance claims, or addressing problems years after completion.
Professional help remains available if you need additional support. Building inspectors can attend inspections and review work quality. The VBA provides guidance and can investigate compliance concerns.
Your investment in proper waterproofing protects your home’s value and your family’s health and safety. Water damage from failed waterproofing affects structural integrity, creates health hazards, and costs exponentially more to fix than proper waterproofing costs initially.
Understanding AS 3740 removes the anxiety many homeowners feel about bathroom renovations. Knowledge gives you confidence to select qualified contractors, verify their work meets standards, and ensure your bathroom protects your home for decades.
Frequently Asked Questions
Can I do bathroom waterproofing myself or must I hire a licensed contractor in Victoria
In Victoria, homeowners can technically do waterproofing on their own property, but there are significant practical and legal points to understand. Only registered building practitioners can issue a Certificate of Compliance, which you'll need as proof the work meets AS 3740 standards. Without this certificate, you may face difficulties selling your property, making insurance claims if water damage occurs, or demonstrating compliance if issues arise. AS 3740:2021 contains specific technical requirements around membrane types, application methods, substrate preparation, falls to waste, and junction treatments that require professional knowledge and experience to execute correctly. Mistakes in waterproofing typically don't become apparent until months or years later when water damage appears, and fixing failed waterproofing requires demolishing the bathroom and starting again. For upper storey bathrooms or bathrooms with timber floors where the entire floor must be waterproofed, the complexity and risk increase substantially. While you might save money on labour by doing it yourself, the risk of costly failures and lack of proper certification generally makes hiring a registered building practitioner the better choice.
What happens if I discover waterproofing defects years after my bathroom renovation was completed
If you discover waterproofing defects years after completion, your options depend on how long ago the work was done and whether the builder is still operating. In Victoria, builders remain liable for structural defects for six years and non-structural defects for two years under Domestic Building Insurance provisions. Beyond these timeframes, or if the builder has died, become insolvent, or disappeared, you may be able to claim on the builder's Domestic Building Insurance if your contract value exceeded $16,000 and DBI was properly arranged. If the builder is still operating within the warranty period, contact them directly in writing outlining the defects and requesting rectification. Document everything with photos and written descriptions. If the builder doesn't respond or refuses to fix issues, lodge a complaint with Domestic Building Dispute Resolution Victoria. For defects discovered outside warranty periods with no DBI coverage, you'll likely need to pay for repairs yourself. This is why keeping all documentation from your original renovation, including Certificates of Compliance, contracts, and photos of the waterproof membrane before tiling, becomes so important.
How can I tell if my existing bathroom waterproofing meets current AS 3740 standards
Determining whether existing bathroom waterproofing meets current AS 3740:2021 standards without destructive testing is challenging because the waterproof membrane sits hidden beneath tiles. However, several indicators can suggest potential problems. Visible signs include mould appearing repeatedly despite cleaning, discolouration or water stains on walls or ceilings adjacent to or below the bathroom, tiles becoming loose or hollow-sounding when tapped, grout constantly cracking or falling out, musty odours in or around the bathroom, and water pooling in the shower rather than draining properly. If your bathroom was built or renovated before 2021, it would have been done to the earlier 2010 version of AS 3740, which had less stringent requirements around membrane grading and falls to waste. Buildings constructed before AS 3740 was introduced may have minimal waterproofing that doesn't meet any current standard. The most reliable way to assess existing waterproofing is to engage a building inspector who can conduct moisture testing, thermal imaging, and visual inspection for signs of water penetration. Remember that even if existing waterproofing met standards when installed, membranes can deteriorate over time, particularly if lower quality products were used.
What is the difference between waterproof and water resistant and where does each apply in my bathroom
Waterproof and water resistant represent different levels of protection against moisture, and AS 3740 specifies which level applies to different bathroom areas. Waterproof means completely impermeable to water, providing a total barrier that prevents any water penetration. Water resistant means able to withstand moisture and occasional water exposure but not designed to be continuously submerged or subjected to direct water spray. In your shower area, everything must be fully waterproof including all walls to 1800mm height, the entire floor, all wall-floor junctions, corners, and any penetrations for taps or fixtures. For unenclosed showers without a full screen, the waterproof floor area must extend 1500mm from the shower rose in all directions. Outside the immediate shower zone, requirements change based on your floor type. For ground floor bathrooms with concrete slab floors, the bathroom floor outside the shower needs to be water resistant. Bathroom walls outside the shower need to be water resistant to 150mm above the floor. However, if your bathroom has timber floors or is on an upper storey, the entire bathroom floor must be fully waterproof. The distinction matters because waterproof membranes are more expensive and require more careful installation than water resistant treatments, but using water resistant products where waterproof is required creates vulnerability to water damage.
Do I need a building permit for bathroom waterproofing work and how does this affect AS 3740 compliance
Building permit requirements for bathroom work in Victoria depend on the scope of your project, but AS 3740 compliance requirements apply regardless of whether a permit is needed. You generally need a building permit if you are constructing a new bathroom, substantially renovating an existing bathroom including structural changes, or doing work that involves significant plumbing alterations. Minor repairs or cosmetic updates that do not affect waterproofing systems typically do not require permits. However, even if your specific project does not require a building permit, any waterproofing work you do must still comply with AS 3740 standards. The standard represents the minimum legal requirement for quality work, not just a permit requirement. If you do need a building permit, the building surveyor will specifically check waterproofing compliance at mandatory inspection stages, particularly after the membrane is applied but before tiling begins. For projects not requiring permits, you are still legally responsible for ensuring work meets building standards, and a registered building practitioner doing the work must still issue a Certificate of Compliance. If problems emerge later, whether from non-compliant work done with or without a permit, you face the same consequences: structural damage, mould issues, repair costs, property value impacts, and potential builder liability claims. When in doubt about whether your project needs a permit, contact the Victorian Building Authority or your local council before starting work.
This article provides general information only and should not be considered professional advice. Building regulations and standards are subject to change. Always consult licensed building practitioners and relevant authorities for advice specific to your project. Information is current as of publication date and accuracy cannot be guaranteed.
