Wet room installation costs and what tanking actually involves
A wet room looks simple once it's finished — a level floor, a glass screen, no visible tray — but the work that makes it possible to walk straight off the floor into a shower without water going everywhere is considerably more involved than fitting a standard bathroom. Understanding what's actually happening under the floor helps explain both the cost and why cutting corners here is a genuinely bad idea.
On typical UK cost guides, a fully fitted wet room commonly comes in somewhere around £5,000 to £14,000, with many standard projects landing around £6,000 to £10,000, or roughly £1,500 to £3,500 per square metre on a like-for-like basis. Within that, the waterproof tanking membrane itself is commonly cited as costing around £500 to £1,500 — a relatively modest line item compared with the room's total cost, which is worth remembering given how much rides on it being done properly. More broadly, labour and preparation — tanking, forming the fall in the floor, and getting the drainage right — is commonly cited as making up around 55 to 65% of a wet room's total cost, more than the visible tiles and fittings, and is repeatedly flagged as the part homeowners most underestimate when comparing quotes.
Tanking, in plain terms, is the continuous waterproof barrier applied to the floor and walls before tiling goes on top. Unlike a standard bathroom, where a shower tray with raised edges and a sealed enclosure does most of the work of containing water, a wet room relies entirely on the floor and walls beneath the tiles being genuinely watertight, since there's no upstand to stop water spreading. This typically means a waterproofing membrane or liquid tanking system applied in full, unbroken coverage across the floor and up the walls to a suitable height, with particular care taken around pipe penetrations, the drain itself, and any corners or junctions, since these are the points most likely to fail if rushed.
Getting the floor to fall correctly toward the drain matters just as much as the waterproofing itself, and on a timber floor this usually means installing a purpose-made wet room former or tray system rather than trying to cut a fall directly into floorboards. A wet room former sits on a reinforced subfloor, typically built up with plywood and additional timber noggins for support, with a waterproof decoupling membrane over the top to manage the natural movement of timber without cracking the waterproofing or tiles above it. Skipping or under-specifying this step is commonly cited as a frequent cause of wet room leaks, separate from tanking failure itself.
The consequences of poor tanking are the reason installers and cost guides treat this as genuinely non-negotiable rather than an area to save money on. Because tanking sits underneath the tiles, a failure is invisible until water has already found a way through, and by the time a problem is visible — as a leak into the room below, a damp patch spreading into an adjoining wall, staining on a ceiling underneath an upstairs bathroom, or a musty smell suggesting mould in the floor build-up — the damage has often already reached the subfloor or timber joists. Repairing this kind of hidden damage typically means ripping out tiling and flooring that looked perfectly fine on the surface, which costs considerably more than doing the tanking properly the first time would have. A wet room's waterproofing, when installed correctly, is generally expected to last the lifetime of the floor covering, which is precisely why it's worth treating as the part of the job least suited to cutting corners.
For anyone planning a wet room, a few practical questions are worth putting to a prospective installer before work starts: what tanking system will be used, and is the installer trained or certified in that specific system by its manufacturer; how will the floor's fall be formed, particularly on a timber floor, and will a purpose-made former be used; and is there a warranty specifically covering the waterproofing, separate from any general workmanship guarantee. A fitter who can answer these clearly and specifically, rather than in vague terms, is generally a good sign that tanking is being treated with the seriousness it needs.
Frequently asked questions
A fully fitted wet room commonly costs around £5,000 to £14,000, with many standard projects landing around £6,000 to £10,000, or roughly £1,500 to £3,500 per square metre on a like-for-like basis; the tanking membrane itself is commonly cited as adding around £500 to £1,500 within that total.
A wet room has no shower tray upstand to contain water, so the floor and walls beneath the tiles must be fully watertight; poor tanking is invisible until water has already got through, and by then it has often damaged the subfloor or timber joists, which is far more costly to fix than doing the tanking properly first time.
A wet room former is a purpose-made unit that creates the correct fall toward the drain on a reinforced, plywood-supported subfloor with a waterproof decoupling membrane over it to manage timber movement; inadequately installed formers are a commonly cited cause of wet room leaks, separate from tanking failure itself.
Labour and preparation — tanking, forming the floor fall, and drainage — commonly make up around 55 to 65% of a wet room's total cost, more than the visible tiles and fittings, which is why this hidden work is often underestimated when comparing quotes.