Wet rooms

What makes a wet room different

In a conventional bathroom, water is contained by a tray and an enclosure, and the tiling is a finish. In a wet room, the floor itself is the containment. Water lands anywhere in the room, runs across the floor to a drain, and the only thing preventing it soaking into the structure is a continuous waterproof membrane underneath the tiles.

That changes the priorities completely. In a normal bathroom, a tiling defect is cosmetic. In a wet room, the tiling is a wearing surface over a waterproof layer, and if the waterproof layer is not continuous, the room will destroy the floor beneath it slowly and invisibly.

It also means every penetration matters. Every screw fixing a screen, every pipe through the floor, every drain flange is a hole in the membrane that has to be sealed as part of the system rather than afterwards with silicone.

Tanking

Tanking is the waterproof membrane – either a liquid-applied system painted on in coats, or a sheet membrane bonded to the substrate, with matching tapes and preformed corners.

• It must be continuous. Floor, up the walls to above shower head height in the wet zone, and to a sensible height everywhere else. Every internal and external corner, every junction, sealed with the system’s own tapes rather than improvised.
• It must be the manufacturer’s complete system. Membrane, primer, tapes, corners, pipe collars and drain flange from one manufacturer, applied in the specified order with the specified coverage and cure times. Mixing systems voids everything.
• Cure times are real. Liquid systems need to cure before tiling. Tiling over uncured membrane traps solvent and the membrane never achieves its properties.
• The substrate must be suitable. Plasterboard is not a wet room substrate. Tile backer board – cement or foam-cored – is, and it is dimensionally stable when wet, which ordinary board is not.
• Pipe penetrations and drain flanges need the system’s own collars, bonded into the membrane. This is where most failures actually occur.

Falls and drainage

Water has to get to the drain, and it only does that if the floor falls towards it from every direction. Achieving that is a physical construction task, done before tiling, and it is the second thing that cannot be fixed afterwards.

How the fall is formed

Either with a preformed sloping former – a rigid board with the falls moulded in, which is the reliable route on a timber floor – or by screeding falls into a solid floor. Preformed formers are used widely because they remove the judgement from an operation that is very hard to do by eye.

Drain type

A centre point drain needs the floor falling in from four directions, which means more complex cutting with large tiles. A linear drain – a slot at one end or along one wall – needs the floor falling in only one direction, which is far easier to tile in large format and generally looks better. Linear drains are more expensive and usually worth it.

Trap depth and flow rate

The drain needs a trap for the smell, and that trap needs depth – which on a timber floor means depth between the joists. This is frequently the constraint that determines whether a wet room is possible at all in a given position, and it needs establishing at survey rather than discovering at strip-out. The drain must also cope with the flow rate of the shower; a high-flow rain head over an under-specified drain produces a flooded floor.

Where the rest of the room drains

Water travels further than people expect. The whole room, not just the shower area, should fall gently towards the drain, or at minimum away from doorways.

Is a wet room right for you?

Honest assessment, because they suit some situations very well and others poorly.

The accessibility case is the strongest one, and it is worth thinking about before it is urgent. A wet room designed now with level access, a drain positioned sensibly and blocking in the walls for grab rails costs very little more than one without, and it means the room does not need rebuilding later. See accessible bathrooms.

Living with one

• Ventilation matters more, because there is more exposed wet surface. An adequately sized extractor with an overrun is essential, not optional.
• Underfloor heating is worth it here, more than anywhere else – it dries the floor between uses, which reduces both slipperiness and mould.
• Choose a slip-resistant tile. A polished porcelain floor in a wet room is genuinely dangerous when wet. Rated slip resistance is a real specification, not a marketing term.
• Expect to squeegee or accept a wet floor. A wet room is not a shower enclosure and water goes where water goes. Most people find a screen on one side is worth having.
• Silicone is a maintenance item, not a permanent one. It should be replaced when it starts to discolour or lift, and on a properly tanked room that is cosmetic rather than urgent.