The short answer
Tanking is the waterproofing that turns a normal floor into a wet room: a continuous membrane bonded across the floor and up the lower walls so water cannot reach the structure behind the tiles. The materials and specialist labour for tanking typically cost £500–£1,000 on a standard shower zone, with the wider floor build-up and drainage adding to that. The floor must be laid to a fall of roughly 10–20mm per metre (about a 1:40 slope) so water runs to the gully — on a timber floor this is usually achieved with a rigid pre-formed former or sloped tray (commonly £450–£550), and on concrete by forming the gradient in the screed. Done properly, tanking is the part of the job you never see but most depend on.
Tanking is the heart of a wet room — the bit a brochure skips and a leak finds. Here is what it involves and what it typically costs to do it correctly.
The waterproofing in brief
- Tanking (shower zone)£500–£1,000
- Pre-formed former/tray~£450–£550
- Tanking rate~£30–£40 per m²
- Drainage fall10–20mm per metre (≈1:40)
- Goalcontinuous, sealed waterproof layer
How tanking and the falls work
- Membrane: a liquid or sheet waterproofing layer is bonded over the floor and up the lower walls, with sealing tape at every joint, corner and pipe penetration so the layer is continuous.
- The former / falls: the floor is laid to a gradient of roughly 10–20mm per metre toward the drain — on timber via a rigid former or sloped tray, on concrete by forming the fall in the screed.
- The gully: a low-profile drain is set at the low point and tied into the tanking so water leaves cleanly.
- Then tiles: tiling goes on top of the cured membrane; the tiles are the finish, not the waterproofing.
| Element | Typical figure | Notes |
|---|---|---|
| Tanking (materials & labour) | £500–£1,000 | standard shower zone |
| Tanking rate | ~£30–£40 / m² | membrane application |
| Former / sloped tray | ~£450–£550 | timber floors mainly |
| Drainage fall | 10–20mm / metre | ≈ 1:40 slope to the gully |
Indicative UK figures for guidance. Sourced UK guidance from BookaBuilderUK and Checkatrade cost guides.
Why it is worth doing properly
Tanking is a hidden cost that is easy to trim on paper and expensive to get wrong. A membrane that is not continuous, a fall that is too shallow, or a gully that is not tied in correctly can let water track into the subfloor and the rooms below — and because it sits under the tiles, fixing it means lifting the floor. This is why the waterproofing is the part of a wet room worth seeing itemised in a quote, and why a measured survey of the subfloor matters before any figure is agreed.
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Frequently asked questions
What is wet room tanking?
Tanking is the waterproofing layer — a continuous membrane bonded across the floor and up the lower walls, sealed at every joint and pipe — that stops water reaching the structure behind the tiles. The tiles are the finish; the tanking is what keeps the room dry.
How much does wet room tanking cost?
The tanking materials and specialist labour for a standard shower zone are typically £500–£1,000, at roughly £30–£40 per square metre. A pre-formed former or sloped tray, used mainly on timber floors, commonly adds £450–£550.
What drainage fall does a wet room need?
The floor is laid to a gradient of roughly 10–20mm per metre toward the drain — about a 1:40 slope — so water runs to the gully instead of pooling. On timber this is set by a former; on concrete the fall is formed in the screed.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific room. They are guidance, not a quotation.