Bathroom waterproofing requirements

In a house bathroom, the shower floor must be waterproofed and the membrane taken up the shower walls to at least 1800 mm, under the National Construction Code housing provisions and AS 3740. Where the floor meets the walls outside the shower, a flashing has to run at least 25 mm up the wall and 50 mm across the floor.

Inside the shower

The membrane covers the whole shower floor and goes up the walls to at least 1800 mm above the floor, whether the shower is hobless, has a hob or has a step-down. Many tilers take it to ceiling height in a walk-in shower because spray from a rain head goes higher.

The rest of the bathroom

Around the walls outside the shower, a perimeter flashing runs at least 25 mm up the wall and 50 mm out across the floor, so water on the floor can't get under the wall lining. Walls next to a bath also need protecting where water splashes.

How it affects what you buy

• Shower base: a polymarble shower base gives a watertight floor without a tiled fall, but the wall junction still needs sealing.
• Channel drain: a tile-insert channel waste has to be bonded into the membrane, so it is fitted before waterproofing, not after.
• Shower niche: a recessed niche breaks into the wall, so the membrane must line it. A stainless niche is set in place before the membrane goes on.
• Shower screen: screw fixings go through the tiles and membrane, so each hole is sealed with silicone. A fixed panel in a wall channel needs fewer holes.