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NZ Building Code · WeathertightnessWet Areas & Waterproofing under E3/AS1
How NZBC clause E3 asks you to tank a shower or wet-area floor so water can’t soak into framing, floors or the unit below.
NZBC clause E3 Internal Moisture is about containing the water generated inside the house — showers, baths, splashing — so it can’t soak into the framing, the floor, or a neighbour’s unit below. In a shower or over a membrane floor you effectively build a watertight tray, or “tanking”: waterproof the floor and lower walls, fall everything to the drain, and seal every penetration. The cited standard is AS/NZS 3740.
The tanking principle
Tiles and grout are not waterproof — water passes through grout and sits on whatever is behind. So the membrane behind the tile is the actual barrier; the tile is just the wearing surface.
- Carry the membrane up the walls.
- Cove the junctions.
- Lap it over the drain flange so any water that gets through the tile is caught and drained, not trapped against the substrate.
Membrane requirements
Use an AS/NZS 4858:2004 wet-area membrane (for example Mapelastic, Bostik Ardex, Sika MaxBond or Equus), applied over the Aqualine substrate. The build-up covers the floor and the lower walls, with the extent depending on whether you’re inside the shower or elsewhere in the wet area.
- Tank the floor and run the membrane 1.8m up the shower walls.
- Take it 150mm up the walls outside the shower.
- Fall the floor to the drain at 1:60 (16.7mm/m).
- Form a 100mm cove upturn at the junctions.
- Fit a 32×32 galvanised metal angle in the internal shower corners (BRANZ Appraisal 427).
Penetrations
Every hole through the tanking is a leak path, so each one gets its own detail:
- Tap penetrations: trim with membrane and ring with sealant.
- Shower drain: rebated into the floor, with the membrane lapped over the flange.
- Mixer trim: sits behind the tile, with the membrane sealed to the body.
Plain-English guide, not advice. This page helps you understand and navigate the rules — it is general information, not design, engineering or consent advice, and it does not reproduce the copyrighted tables of NZS 3604 or any Standard. Always check the current Standard or Acceptable Solution and your BCA, and use a suitably qualified LBP, engineer or QS where it matters.
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Common questions
What is NZBC clause E3 actually trying to achieve?
E3 Internal Moisture is about containing the water generated inside the house — showers, baths and splashing — so it can’t soak into the framing, the floor, or a neighbour’s unit below. The cited standard is AS/NZS 3740.
If the tiles are sealed, why do I still need a membrane behind them?
Tiles and grout are not waterproof — water passes through the grout and sits on whatever is behind. The membrane behind the tile is the actual barrier; the tile is just the wearing surface.
How high does the membrane go, and what fall does the floor need?
Tank the floor and carry the membrane 1.8m up the shower walls, and 150mm up the walls outside the shower. The floor is falled to the drain at 1:60, which is 16.7mm per metre.
How do I detail the taps, drain and mixer through the tanking?
Tap penetrations are trimmed with membrane and ringed with sealant. The shower drain is rebated into the floor with the membrane lapped over the flange. The mixer trim sits behind the tile with the membrane sealed to the body.
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