Wet Area Waterproofing (NZ E3/AS1)

The requirement

E3/AS1 is the Acceptable Solution for Building Code clause E3 “Internal Moisture” — the recipe most bathrooms are built to. It sets impervious surfaces at different heights depending on what’s underneath them, not one number for the whole room (E3/AS1, Paragraph 3.3.1 “Showers” and Paragraph 3.2.2 “Joints between fixtures and wall linings”).

Inside the shower, the impervious wall lining has to be sealed to the wall behind it at its top edge — or run all the way to the ceiling — so condensation can’t get in behind the lining. Penetrations for tapware, mixers and roses have to be waterproofed with a proprietary flange or sealant that still allows access for servicing.

1. 1 shower floor
2. 2 basin / bath

The rest of the floor

Outside the shower, E3/AS1 still asks for protection at every point water can get behind a lining or under a floor finish:

• Floor-to-wall junctions. Where a floor covering meets a wall, at least 75 mm of water-resistant wall lining is required above the junction, and the floor covering itself has to be coved or sealed at the join — vinyl coved continuously, tiles coved or sealed at the edge.
• Open-plan wet areas. Where there’s no wall separating the wet fixtures from the rest of an open-plan room, the impervious floor surface has to extend 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, the joint between the base of the fixture and the floor has to be sealed.

AS1 is one path, not the only one

E3 itself is performance-based — it asks for surfaces that are impervious and easily cleaned, without naming a height. E3/AS1 is the Acceptable Solution: the recipe MBIE writes that a council treats as automatically compliant. It’s the standard route, but a designer can instead use a Verification Method or an Alternative Solution, which may set different numbers. The figures above are the AS1 path.

On site — what to waterproof

1. Shower walls — impervious lining up to the higher of 1800 mm above the floor or 50 mm above the rose, sealed at the top edge.
2. Shower floor — impervious across the whole enclosure, or out to a 1500 mm radius from the rose if there’s no enclosure.
3. Bath, basin, tub and sink walls — 150 mm minimum upstand, sides and back, sealed to the fixture.
4. Floor-wall junctions elsewhere — 75 mm min water-resistant lining above the join, floor covering coved or sealed at the edge.
5. Open-plan wet areas — impervious floor extending 1.5 m from every sanitary fixture where there’s no wall to contain it.
6. Penetrations — waterproof tapware, mixer and rose penetrations with a proprietary flange or sealant that still allows 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 — 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.