Wet Area Waterproofing (NZ E3/AS1)

The requirement

In a shower, the waterproof wall lining must reach 1800 mm above the shower floor. If 50 mm above the shower rose is higher, go to that instead. Walls at a bath, basin, tub or sink need a 150 mm upstand. That’s E3/AS1, Paragraph 3.3.1 “Showers” and Paragraph 3.2.2 “Joints between fixtures and wall linings”.

E3/AS1 is the Acceptable Solution for Building Code clause E3 “Internal Moisture”. It’s the recipe most bathrooms are built to. The code word for waterproof here is “impervious”: water cannot get through the surface. The height you need depends on what sits under the wall, not one number for the whole room.

Inside the shower, seal the top edge of the lining to the wall behind it. Or run the lining all the way up to the ceiling. That stops condensation getting in behind it. Holes for tapware, mixers and roses must be waterproofed too. Use a proprietary flange or sealant. You still need access to service them.

1. 1 shower floor
2. 2 basin / bath

The rest of the floor

Outside the shower, E3/AS1 still guards every spot where water can get behind a lining or under a floor finish:

• Floor-to-wall junctions. Where a floor covering meets a wall, you need at least 75 mm of water-resistant wall lining above the junction. Cove or seal the floor covering at the join. Vinyl gets coved up the wall in one run. Tiles get coved or sealed at the edge.
• Open-plan wet areas. No wall between the wet fixtures and the rest of the room? Then the impervious floor must run at least 1.5 m out from every sanitary fixture or appliance.
• Fixture-to-floor joints. Where a bath, basin, tub or sink sits on an impervious floor finish, seal the joint between the base of the fixture and the floor.

AS1 is one path, not the only one

Clause E3 itself is performance-based. It asks for impervious, easily cleaned surfaces, but names no height. E3/AS1 is the Acceptable Solution: the recipe MBIE writes. A council treats work built to it as meeting the code. A designer can use a Verification Method or an Alternative Solution instead. Those can set different numbers. The figures above are the AS1 path.

On site — what to waterproof

1. Shower walls. Lining up to the higher of 1800 mm above the floor or 50 mm above the rose. Seal the top edge.
2. Shower floor. Impervious across the whole enclosure. No enclosure? Go out to a 1500 mm radius from the rose.
3. Bath, basin, tub and sink walls. A 150 mm minimum upstand, sides and back, sealed to the fixture.
4. Floor-wall junctions elsewhere. At least 75 mm of water-resistant lining above the join. Cove or seal the floor covering at the edge.
5. Open-plan wet areas. No wall to hold the water? The impervious floor runs 1.5 m out from every sanitary fixture.
6. Penetrations. Waterproof the tapware, mixer and rose holes with a proprietary flange or sealant. Leave access for servicing.

Related

• Part of the New Zealand Building Code hub. One national rule book, no regional variations.
• Building the room around it? See NZ minimum ceiling heights. It covers what the Building Code does and doesn’t set for a bathroom ceiling.
• Setting out the wet-area floor falls and floor waste is a plumbing job. Check with your plumber and NZBC Clause G13 Foul Water.

Sources

• NZ Building Code Acceptable Solution E3/AS1 (2nd edition, Amendment 7, effective 5 November 2020), Paragraph 3.3.1 “Showers,” Paragraph 3.3.1.1 “Shower floor materials,” Paragraph 3.2.2 “Joints between fixtures and wall linings,” Paragraph 2.1.1 “Containment,” and Paragraph 3.1.1 “Floors” — the 1800 mm / 50 mm shower-wall height, the 1500 mm shower- floor radius, the 150 mm fixture upstand, the 75 mm floor-junction lining, and the 1.5 m open-plan floor extent. Free official PDF via building.govt.nz. (Confirmed by direct text extraction from the official MBIE PDF, verified 2026-07-31.)
• Acceptable Solution vs compulsory path: E3/AS1 is a deemed-to-comply route for Building Code clause E3 Internal Moisture, not the only legal way to comply. A designer can use a Verification Method or an Alternative Solution instead, which can carry different figures. Always check the current amendment on building.govt.nz before you sign off on a job.