After 25 years working in the waterproofing industry across Brisbane, I've seen firsthand the consequences of non-compliant waterproofing work. From structural damage costing tens of thousands to repair, to health issues from mould growth, the stakes are high when waterproofing isn't done right.
In this comprehensive guide, I'll break down everything you need to know about Australian waterproofing standards and why they matter for your project.
What is AS 3740?
Australian Standard AS 3740 is the national standard for waterproofing of domestic wet areas. It sets out the minimum requirements for the design, selection of materials, and installation of waterproofing systems in residential buildings.
First published in 1994 and regularly updated, AS 3740 is referenced by the National Construction Code (NCC) and is mandatory for all waterproofing work in wet areas across Australia.
Important: AS 3740 is not optional
Many homeowners don't realise that AS 3740 compliance isn't a "nice to have" – it's a legal requirement. Any waterproofing work in your home's wet areas must meet this standard, and in Queensland, it must be carried out by a QBCC licensed waterproofer.
The National Construction Code (NCC)
The National Construction Code (NCC) is Australia's primary set of technical design and construction provisions for buildings. It incorporates the Building Code of Australia (BCA) and the Plumbing Code of Australia (PCA).
The NCC references AS 3740 as a deemed-to-satisfy solution for waterproofing, meaning if you comply with AS 3740, you satisfy the NCC's performance requirements for waterproofing.
Key NCC Requirements for Waterproofing:
- Performance Requirement: Building elements must be constructed to prevent moisture penetration that could cause unhealthy conditions, loss of amenity, or damage to building elements
- Durability: Waterproofing systems must remain effective for the life of the building
- Materials: Only approved materials meeting relevant Australian Standards can be used
- Installation: Work must be carried out by licensed practitioners according to manufacturer specifications
Where is Waterproofing Required?
AS 3740 specifies the areas in domestic buildings that require waterproofing. These "wet areas" include:
Bathrooms & Ensuites
Shower recesses, bath surrounds, and floors require comprehensive waterproofing membranes
Laundries
Floor areas and walls around tubs and sinks need proper moisture protection
Balconies & Terraces
External wet areas require UV-resistant systems with proper drainage
Water Closets
Toilet areas need appropriate waterproofing around fixtures
Key Requirements of AS 3740
1. Substrate Preparation
The substrate (surface being waterproofed) must be:
- Clean and free from contaminants
- Structurally sound with no movement or deflection issues
- Properly primed according to membrane manufacturer specifications
- Free from sharp edges or protrusions that could damage the membrane
2. Membrane Selection & Application
Waterproofing membranes must:
- Be appropriate for the substrate type and exposure conditions
- Be applied in accordance with manufacturer specifications
- Achieve minimum thickness requirements (typically 2 coats for liquid membranes)
- Include reinforcement fabric at critical junctions and changes of plane
3. Critical Details
Special attention is required at:
- Internal corners: Minimum 75mm strip of membrane reinforced fabric
- External corners: Minimum 100mm wide reinforced strips
- Floor waste outlets: Sealed connection between membrane and waste
- Penetrations: All pipes, fixtures, and fittings must be properly sealed
- Change of plane junctions: Where walls meet floors, proper detailing is critical
4. Height Requirements
AS 3740 specifies minimum membrane heights:
- Shower recesses: Minimum 1800mm high on walls
- Hobs (step-downs): Minimum 100mm high (75mm in certain conditions)
- Bathroom walls: Minimum 150mm above floor level, or to underside of bath
- Balconies: Entire floor area plus upturns to required heights
5. Flood Testing
All shower areas must be flood tested:
- Test must be conducted for a minimum of 24 hours before tiling
- Water level must be maintained at the height of the hob or floor waste
- Any leaks must be identified and rectified before proceeding
- Test results should be documented with photos and dates
Pro Tip: Documentation Matters
Always ensure your waterproofer provides detailed documentation including photos of membrane application, flood test results, and certification. This is crucial for warranty claims and if you ever sell your property.
Queensland-Specific Requirements (QBCC)
In Queensland, the Queensland Building and Construction Commission (QBCC) adds additional requirements:
Licensing Requirements
- All waterproofing work must be carried out by a QBCC licensed waterproofer
- Homeowners cannot do their own waterproofing work in Queensland
- The license number must be included on all quotes and invoices
- Licensed waterproofers must maintain appropriate insurance
Compliance Certificates
For building work requiring a building approval, a Form 4 (Certificate of Classification) or Form 21 (Certificate of Final Inspection) may be required. Your waterproofer should provide appropriate certification documenting compliance with AS 3740.
Common Non-Compliance Issues I See
Over my 25 years in the industry, these are the most common problems I encounter:
1. Insufficient Membrane Coverage
Membranes not extending to required heights, particularly in shower areas. I regularly see membranes only 1200-1500mm high when AS 3740 requires 1800mm minimum.
2. Poor Junction Detailing
Corners, penetrations, and floor-to-wall junctions inadequately sealed. These are the most common failure points and require careful attention to detail.
3. Inadequate Substrate Preparation
Membranes applied over contaminated, damp, or structurally unsound substrates. The membrane is only as good as what it's bonded to.
4. Wrong Membrane Selection
Using internal wet area membranes on external balconies, or vice versa. External areas require UV-resistant systems that can handle temperature extremes.
5. No Flood Testing
Skipping the flood test to save time. This is mandatory under AS 3740 and is your only way to verify the membrane is watertight before tiling.
6. Unlicensed Work
DIY installations or work by unlicensed tradies. In Queensland, this is illegal and will void any insurance coverage if problems arise.
Consequences of Non-Compliance
The ramifications of non-compliant waterproofing extend far beyond code violations:
Financial Impact
- Repair costs: Rectification often requires complete tile removal and re-waterproofing – typically $8,000-$25,000 for a standard bathroom
- Consequential damage: Water damage to structural timber, ceiling damage to rooms below, mould remediation
- Property value: Disclosure requirements when selling can significantly impact sale price
- Insurance issues: Claims may be denied if work wasn't compliant or licensed
Health & Safety
- Mould growth from persistent moisture causes respiratory issues
- Slip hazards from water escaping wet areas
- Structural integrity compromised by water damage to timber frames
Legal Ramifications
- QBCC penalties for unlicensed work
- Difficulty obtaining building approvals for renovations
- Liability issues if selling property with known non-compliance
- Potential disputes with builders or contractors over responsibility
How to Ensure Compliance
Here's what I recommend to all my clients:
Before the Work Starts
- Verify licensing: Check your waterproofer's QBCC license is current at qbcc.qld.gov.au
- Get detailed quotes: Ensure quotes specify AS 3740 compliance and include flood testing
- Discuss the system: Understand what membrane system will be used and why it's appropriate
- Check insurance: Confirm appropriate insurance coverage is in place
During Installation
- Request progress photos: Document each stage of membrane application
- Verify flood test: Be present for flood test initiation and check after 24 hours
- Review critical details: Check corner treatments and penetration seals
- Ask questions: A good waterproofer will happily explain their process
After Completion
- Obtain documentation: Get photos, flood test results, product data sheets, and certification
- Understand warranties: Know what's covered by workmanship warranty vs manufacturer warranty
- Keep records: Store all documentation safely – you'll need it for insurance or future sale
- Schedule inspections: Regular visual checks can identify problems early
The Bottom Line
Waterproofing might not be the most visible part of your renovation, but it's one of the most critical. Cutting corners on compliance to save a few hundred dollars can cost you tens of thousands down the track.
As a licensed waterproofing specialist with 25 years of experience, I've built my reputation on doing things right the first time. Every project we complete is fully AS 3740 compliant, properly documented, and backed by comprehensive warranties.
Frequently Asked Questions
Q: Can I waterproof my own bathroom in Queensland?
A: No. Unlike some other states, Queensland law requires all waterproofing work to be carried out by a QBCC licensed waterproofer. This protects homeowners and ensures compliance with Australian Standards.
Q: How long does waterproofing take?
A: A typical bathroom takes 1-2 days for membrane application, plus a minimum 24-hour flood test before tiling can proceed. Rushing this process compromises quality and compliance.
Q: What's the difference between water-based and polyurethane membranes?
A: Water-based membranes are easier to apply, have less odour, and include an 8-year manufacturer warranty. Polyurethane thick membrane systems are more robust, suited to difficult substrates, and carry up to 20-year warranties. Both can be AS 3740 compliant when properly installed.
Q: Do I need waterproofing if I'm just replacing tiles?
A: If the existing waterproofing is compromised, failed, or non-compliant, then yes – the area must be re-waterproofed. We recommend inspection before any tile replacement to assess the existing system.
Q: How do I know if my existing waterproofing has failed?
A: Warning signs include: water stains on ceilings below, damp patches on walls, tiles becoming loose or hollow-sounding, mould growth, or musty odours. If you notice any of these, get a professional assessment immediately.
Need Compliant Waterproofing?
At Spartan Waterproofing, every job we undertake is completed to the highest standard with full AS 3740 and NCC compliance. Our QBCC license (15456097), 25 years of experience, and 5.0-star rating speak to our commitment to quality and compliance.
We provide detailed documentation, comprehensive flood testing, and industry-leading warranties on all our work. Whether it's a new build, renovation, or remedial work, we ensure your waterproofing is done right – the first time.