Waterproofing your bathroom or shower might seem straightforward, but in New Zealand it's governed by specific building regulations that exist to protect your home from serious moisture damage. Getting it wrong can lead to rotting framing, mould, and costly repairs — so understanding the rules before you start is essential.
What Is Clause E3 of the NZ Building Code?
Clause E3 (Internal Moisture) is the section of the NZ Building Code that deals with moisture inside buildings. Its core requirement is that buildings must be constructed to prevent water from causing damage to building elements, or creating conditions that are unhealthy for occupants. For wet areas like showers, baths, and laundries, this means surfaces must be waterproofed so that water cannot penetrate into the structure behind them.
The acceptable solutions for meeting E3 are primarily found in E3/AS1, which sets out specific requirements for wet area construction including membrane types, upstand heights, and substrate preparation.
Which Areas Must Be Waterproofed?
Under E3/AS1, the following areas typically require waterproofing:
- Shower enclosures — the floor and walls to a minimum height (generally at least 1800 mm above the shower floor, or to the full height of tiled walls)
- Bath surrounds — walls adjacent to the bath, typically to a minimum of 100 mm above the bath rim
- Laundry floors — where a tub or washing machine is located
- Floors in bathrooms — particularly where floor waste drains are present
- Balconies and decks — covered under related clauses where water can penetrate to habitable spaces below
Always check the specific upstand and coverage requirements in E3/AS1, as dimensions can vary depending on the construction type and substrate.
Acceptable Waterproofing Systems
Not all waterproofing products are equal under the Building Code. Systems must be fit for purpose and, where used as an Alternative Solution, may require specific documentation. Common compliant approaches include:
| System Type | Common Use | Notes |
|---|---|---|
| Sheet membranes (e.g. PVC, CPE) | Shower floors, wet area floors | Robust, long-lasting |
| Liquid-applied membranes | Walls and floors under tiles | Must be applied to correct thickness |
| Tanking systems | Full bathroom waterproofing | Suits high-risk or below-ground areas |
| Compressed fibre cement sheet | Substrate behind tiles | Must be used with a membrane |
Products from suppliers like Ardex, Mapei, and Sika offer liquid-applied membrane systems commonly used in NZ wet areas. Always follow the manufacturer's application instructions precisely — coverage rates and cure times matter for compliance.
Substrate Requirements
The surface you apply waterproofing to is just as important as the membrane itself. Key points:
- GIB standard plasterboard is NOT suitable as a substrate in wet areas — you must use a moisture-resistant board or fibre cement sheet
- Fibre cement sheet (such as products from James Hardie) is a common and compliant substrate for tiled wet areas
- Substrates must be structurally sound, clean, and free of movement before membrane application
- Sheet joints and penetrations (pipes, screws) must be properly sealed before the membrane is applied
Do You Need a Building Consent?
This is a critical question. In New Zealand, replacing like-for-like waterproofing during a repair may not require consent, but any alteration to a wet area — such as retiling a shower, moving a drain, or renovating a bathroom — often does require a building consent from your local council.
Work done without the required consent can cause problems when you sell your home and may not be covered by your insurance. Check with your local council or visit MBIE Building Performance to confirm whether your project needs consent before starting.
What Can a Homeowner Do Themselves?
Some preparatory and finishing work can be done by a competent homeowner, including:
- Removing old tiles and substrate (take care with older homes that may have asbestos-containing materials — check with WorkSafe NZ if unsure)
- Applying liquid waterproofing membranes to prepared substrates (if no consent is required)
- Tiling over a correctly waterproofed surface
However, the quality of waterproofing application is critical. Missed spots, insufficient thickness, or poorly sealed penetrations are common DIY failure points.
When to Call a Professional
Some work in wet areas is legally restricted and must be carried out by a licensed tradesperson:
- Plumbing and drainlaying — moving or installing waste pipes, floor wastes, or water supply connections must be done by a licensed plumber or drainlayer registered with the Plumbers Gasfitters & Drainlayers Board
- Electrical work — installing or moving lights, fans, or heated towel rails in bathrooms is restricted electrical work requiring a registered electrician (EWRB)
- Restricted building work — certain structural or weathertightness work must be carried out or supervised by a Licensed Building Practitioner (LBP)
Even for non-restricted waterproofing work, hiring an experienced waterproofing professional is strongly recommended. A botched waterproofing job is one of the most expensive mistakes a homeowner can make. You can find qualified local waterproofers and tilers on tradedirectory.co.nz.