London Wet Room Installation — BS 8000 Tanking, Joist Loading, Leasehold

A London wet room is a bathroom where the floor is the shower tray — and every London builder who has built one badly has a leak claim in their history. Unlike a standard bathroom with a raised tray, a wet room tanks the entire floor and lower-wall surface, drains through a floor gully, and relies on fall-to-drain geometry that is set by the joists underneath. Get the joist loading wrong and the floor bounces — which cracks the tanking — and you are back to square one.

On a London flat, add the leasehold reality: a wet-room conversion almost always requires a Licence to Alter because it touches the soil pipe, the floor structure, and frequently the ventilation strategy. On a listed or conservation-area property, add Listed Building Consent or a conservation-area consent check because the historic floor structure cannot just be cut up for drainage.

AskBaily routes London wet-room installations to a builder who specifies BS 8000-grade tanking, delivers joist-loading calcs, and has the Part P competent-person certificate for the rewire.

Wet-room compliance checklist

• Tanking. BS 8000-grade CE-marked membrane (Schlüter-KERDI, Dural, Wedi, Mapei Mapelastic) on floor + 1.8 m up walls. Corners reinforced. Gully flange embedded.
• Fall to drain. Minimum 1:50 fall to a channel or square gully. Joist-level pre-fall or screed-level post-fall.
• Joist loading. Structural engineer's confirmation for loaded tile + mortar + screed on timber joists.
• Ventilation. Part F mechanical extract. For Inner London flats with limited external-wall access, in-line fan + duct through adjacent room.
• Electrics. Part P Zone 0/1/2 fittings, RCD-protected, competent-person certification.
• Leasehold. Licence to Alter for floor structure and soil-pipe work.

Frequently asked questions

Can I install a wet room in a leasehold flat? Usually yes, but not without a Licence to Alter from the freeholder. The freeholder's surveyor will check floor structure, soil-pipe compatibility, and fire-compartmentation. Expect 6-12 weeks for consent.

How much does a London wet room cost? £12,000-£30,000 for a mid-spec Inner London flat wet room. £40,000-£90,000 for a prime-central master wet room with bespoke stone, in-floor heating, and rainfall shower. 25-40% premium over a standard bathroom.

Do I need Building Control sign-off? Yes for the ventilation strategy, any rewire, and often the structural alteration. Part F, Part P, and Approved Document A are in play. A Building Notice is usually simpler than Full Plans for a self-contained wet room.

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