compliance7/31/2026
Australian Waterproofing Standard AS 3740 Explained: Bathroom & Wet Area Requirements
Waterproofing is one of the most common defect sources in Australian construction. This guide covers AS 3740 key requirements including membrane heights, material selection, and acceptance criteria.
## Why Waterproofing Matters
Waterproofing issues consistently rank in the top three building defect complaints in Australia. Waterproofing failure causes not only structural damage but also mould health issues, with expensive remediation costs. Correct waterproofing is critical to protecting building investments.
## AS 3740 Core Requirements
### Shower Areas
- **Floor**: Entire shower area floor must be waterproofed
- **Walls**: Minimum 1800mm height from floor
- **Threshold**: Shower areas must have a hob or step-down
- **Fall**: Floor gradient 1:60 to 1:80 toward drain
### Bath Areas
- **Floor**: Under and around bathtub must be waterproofed
- **Walls**: Minimum 150mm above bath edge
- **Overflow**: Consider overflow scenarios around bath
### Vanity Areas
- **Floor**: Around vanity must be waterproofed
- **Walls**: Minimum 150mm in splash zones
- **Back wall**: Full-height waterproofing recommended
### Laundry
- **Floor**: Entire laundry floor must be waterproofed
- **Walls**: Behind washing machine and trough minimum 150mm
### Balcony
- **Floor**: Entire balcony floor must be waterproofed
- **Walls**: Adjacent interior walls minimum 150mm
- **Drainage**: Must have independent drainage system
## Waterproofing Material Selection
| Material Type | Application | Pros | Cons |
|--------------|-------------|------|------|
| Liquid membrane | Bathrooms, kitchens | Easy application, seamless | Multiple coats needed |
| Sheet membrane | Large floor areas | Uniform thickness, reliable | Complex joint treatment |
| Polyurethane | Balconies, roofs | Flexible, weather resistant | Higher cost |
| Cement-based | Basements, pools | Bonds well with concrete | Less flexible |
## Key Installation Points
1. **Substrate preparation**: Ensure surface is dry, flat, and free of contaminants
2. **Corner reinforcement**: All internal corners require non-woven reinforcement strips
3. **Coating thickness**: Liquid membrane dry film thickness minimum 1.5mm
4. **Drying time**: Minimum 4-6 hours between coats
5. **Flood testing**: 24-48 hour flood test after completion
6. **Protection**: Protective layer over membrane before tiling
## Common Mistakes
- ❌ Insufficient membrane height (shower area below 1800mm)
- ❌ No corner reinforcement
- ❌ Tiling before membrane fully cured
- ❌ Poor waterproofing around floor waste
- ❌ Using non-compliant waterproofing materials
- ❌ No flood testing performed
## BuildBridge Waterproofing Products
BuildBridge Australia offers Australian Standards-compliant waterproofing coatings and accessories, including flexible polymer-cement membranes, corner reinforcement strips, and floor waste waterproofing kits. All products include installation guidance.
*Sources: Standards Australia AS 3740, Master Builders Association, Building Commission Victoria*
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