By the WetRoomGuide.co.uk — Expert Advice & Product Reviews for UK Wet Rooms Team · Updated June 2026 · Independent, reader-supported

How to Build a Wet Room UK: Step-by-Step DIY Guide

A wet room is an increasingly popular bathroom style where the shower area is fully waterproofed and seamlessly integrated into the main bathroom floor. There's no shower tray, no cubicle—just a sloped floor that drains to a single point. They look modern, maximise small spaces, and are genuinely accessible for older people or those with mobility issues. Building one yourself is possible, but it demands precision and honest assessment of your skills. This guide walks you through the process so you know what you're taking on.

Check Your Subfloor First

Before ordering anything, inspect what you're working with. Wet rooms work best on solid concrete or well-braced timber joists. If your bathroom is on an upper floor with older joists, you need to check deflection—the floor should move less than 3mm when you jump on it. Excessive bounce means the waterproofing will crack over time. Concrete ground floors are ideal. If you're on timber and it's borderline, consider reinforcing joists or calling a surveyor.

Also check your existing pipework. You'll need access to soil and waste pipes, and ideally somewhere to run the wet room drain without major rerouting. If new drainage means opening up walls or breaking out concrete, costs and complexity escalate quickly. Be realistic about what you can do in a weekend.

Plan the Slope and Drainage

The entire floor must slope gently towards a central drain—typically 1:40 (2.5cm drop per metre). You can't eyeball this. You'll need to mark out levels using a spirit level or laser level, then build up the subfloor using screed or self-levelling compound to achieve it. This is tedious but non-negotiable; a shallow slope still leaves pooling water.

Choose your drain position first. Linear drains (which run along one edge) need less slope than point drains, but cost more and are trickier to install. Point drains are standard in DIY wet rooms. A 50mm or 75mm drain should handle normal shower usage in a typical bathroom.

Prepare the Subfloor

Strip everything back to bare concrete or timber. Fill any pits or depressions. Sand down high spots. The surface needs to be relatively smooth and sound—no crumbling concrete or rotting wood.

If you're working on timber, lay a moisture barrier (polythene sheet) to stop rising damp underneath. Then either lay a cement screed or use a purpose-made wet room base board. The base board option (systems by brands like Wedi or Schluter) is harder to get wrong than mixing and laying screed by hand. It's denser, won't sag, and handles slight unevenness better. Screed is cheaper but demands more skill and patience.

Apply the Tanking System

This is the most critical step. Your waterproofing must be complete or the whole thing fails. There are two main approaches:

Liquid tanking kits are polyurethane or polyacrylic membranes you roll or spray onto the subfloor and walls. They're forgiving on the application—small oversights in coverage usually aren't fatal—and don't require special skills. Expect to apply multiple coats. The downside is drying time between coats (can stretch the job over several days) and you need to ensure full overlap and coverage on corners. Look for kits certified to BS 6414 (British Standard for waterproofing) and follow the manufacturer's instructions exactly. Poor ventilation while curing is a common mistake.

Sheet membranes (rubber or PVC) are pre-made and sealed at seams. They're faster and arguably more foolproof if seams are done properly, but that's also where failures happen. You're relying on adhesives and sealants to bond at seams and corners, which leaves room for error if you're inexperienced.

For a DIY build, a liquid system from a brand with a clear instruction sheet is usually safer. Extend the tanking 300mm up the walls and seal all penetrations (pipes, drains) with dedicated corner and pipe seals from the same system.

Install the Wet Room Former and Drain

Once tanking is set, install your wet room former—this is the prefabricated floor section with the built-in slope. It sits on the tanking and connects to the drain. Alternatively, you can build the slope using screed or a mortar bed, but a purpose-made former removes the guesswork.

Install the drain according to the manufacturer's instructions. The drain connection is critical—use the correct coupling, apply silicone sealant generously, and test the seal before proceeding. Block the drain opening with a temporary cover to keep screed and tile adhesive out.

Tile or Finish the Surface

Once the former is set and the tanking has fully cured (check drying times—often 24–48 hours), tile the floor. Use a waterproof tile adhesive (rapid-set or standard, doesn't matter as long as it's rated for wet areas) and non-sanded grout for joints under 6mm, or sanded grout for wider joints. Grout all joints completely.

Apply a grout sealant in the corners where the floor meets the walls and around the drain—this stops water creeping into substrate. Many wet room problems are actually caused by water getting under the waterproofing, not through it, because sealant was skipped.

When to Call a Professional

If you're uncomfortable with levels, slopes, or waterproofing, call a specialist. Ripping out a failed wet room costs hundreds and takes weeks. A professional surveyor-checker during planning (£100–200) is the cheapest insurance. Similarly, if your drainage involves major works or your floor structure is weak, get a structural engineer involved before you start.

The Reality

A wet room done properly is beautiful and long-lasting. Done badly, it's a source of mould, smell, and expensive repairs. The tanking and slope are not areas to cut corners. Build it once, build it right.