Plumbing

Wet Room Installation Guide

Name: TradePlanr
Rating: 5 (100 reviews)
Author: TradePlanr

A wet room lives or dies on the waterproofing you cannot see. Get the tanking, the falls and the drainage right and it lasts for decades; skip a step and it finds the ceiling below.

Updated 23 Aug 20269 min read

A wet room is not just a shower without a tray — it is a fully waterproofed floor and wall area where the whole room is the shower enclosure. That makes the hidden work, the tanking and the falls, far more important than the tiles anyone actually sees.

This guide covers the parts that matter to getting it watertight: substrate and formers, floor falls to the drain, tanking and waterproofing, and the build sequence that stops water reaching the structure below.

Key takeaways

The waterproofing (tanking) is the job — tiles are decoration over the top of it.
The floor must fall towards the drain; a pre-formed sloped former is the reliable way to achieve consistent falls.
Tank the whole floor and the wet walls to a sensible height, lapping the membrane into the drain flange.
On timber floors, brace and stiffen the deck first — movement cracks tiling and, worse, the waterproof layer.
Follow the sequence: substrate, drain, falls, tank, test, then tile. Skipping the test risks a ceiling below.

Substrate and floor former

Everything starts with a stable, flat and dry substrate. On a solid floor you can form falls in screed or use a pre-formed former; on a timber floor you need to stiffen the deck first, because any deflection will crack the tanking and the tiles. A tile-backer or purpose-made wet room former gives you a rigid, waterproof base to build on.

A pre-formed sloped former is the low-risk route to consistent falls into the drain. It takes the guesswork out of getting an even slope from every direction, which is where hand-formed falls most often go wrong.

Falls and drainage

Water has to run to the drain from wherever it lands, so the whole showering area needs a consistent fall — too shallow and it pools, too steep and it feels odd underfoot and cracks large-format tiles. A linear drain against a wall or a centre gully both work; the key is matching the former, the drain position and the fall together.

Choose a drain with the flow rate to match the shower and a removable trap you can actually clean. The membrane laps into the drain's clamping flange so the waterproof layer and the drain are continuous — this junction is the single most common leak point in a wet room.

The drain junction is where leaks start

More wet rooms fail at the membrane-to-drain connection than anywhere else. Use a drain designed to clamp the tanking membrane, and follow the manufacturer's lap detail exactly.

Tanking and waterproofing

Tanking is the continuous waterproof membrane that turns the room into a sealed tray. Whether you use a liquid membrane or a sheet system, the whole floor and the wet walls must be covered to a sensible height, with reinforcing tape or matting worked into every internal corner, the wall-to-floor junction and around the drain and pipe penetrations.

Give each coat the manufacturer's stated drying time before the next, and before you tile. Rushing the tanking to keep the job moving is how water eventually finds a pinhole. The membrane is the part doing the actual waterproofing — the tiles and grout are not a waterproof layer.

Sequence, testing and pricing

Work in order: prepare the substrate, set the drain, form the falls, tank and reinforce the junctions, then flood- or water-test before a single tile goes down. Testing at this stage is cheap insurance; discovering a leak after tiling and after the ceiling below is decorated is not.

For pricing, a wet room carries more labour than a standard shower enclosure because of the tanking, the falls and the drainage — price it as its own line, not as a like-for-like of a tray install, and flag any timber-floor strengthening as separate work.

Price the hidden work, not just the tiles

Build the wet room quote in TradePlanr from separate lines for substrate prep, drainage, tanking and tiling, so the waterproofing labour is priced and visible — then convert the accepted quote straight to an invoice.

Frequently asked questions

Do I have to tank a wet room?

Yes. Tanking is the continuous waterproof membrane that makes a wet room work — tiles and grout are not a waterproof layer. The whole floor and the wet walls must be tanked, with junctions and penetrations reinforced.

Can you put a wet room on a timber floor?

Yes, but the deck must be stiffened first so it does not deflect, because movement cracks both the tanking and the tiles. Use a rigid tile-backer or purpose-made former over a braced, level timber floor.

Where do wet rooms usually leak?

Most commonly at the membrane-to-drain junction and at unreinforced internal corners. Use a drain designed to clamp the tanking membrane, reinforce every corner and junction, and water-test before tiling.

From guidance to action

Quotes & estimatesPrice wet-room work from separate lines for tanking, drainage and tiling.Certificates on your phoneIssue commissioning and compliance records as PDFs, stored on the job.TradePlanr for plumbersQuotes, certificates and invoicing built for plumbing work.