UK Wet-Area Waterproofing: What Approved Document C Doesn't Cover

The requirement

Here’s the honest answer: Approved Document C sets no wet-area waterproofing requirement at all. There is no clause number to cite for a shower wall, a wet-room floor, or a bath upstand — because Approved Document C never mentions bathrooms, showers or wet rooms.

Approved Document C — “Site preparation and resistance to contaminants and moisture” — is the statutory guidance to Part C of the Building Regulations 2010. Its scope is the building envelope: ground moisture and contaminants under the slab, moisture penetrating external walls, and weathertightness of roofs. It does not step inside the building to deal with a shower recess or a wet-room floor at all. Reading the whole document looking for a shower-wall height or a membrane spec, the way you’d find one in Australia’s NCC or the US IRC, turns up nothing — that gap is real, not a case of missing the right paragraph.

So if you’ve been told “the regs say” a shower wall needs waterproofing to a given height in England or Wales, that instruction isn’t coming from Approved Document C. It’s coming from somewhere else — and that somewhere else is a standard this page can name, but not reproduce.

Where the actual numbers live

Bathroom and wet-room tanking in the UK is driven in practice by BS 5385-1:2018 — “Wall and floor tiling. Design and installation of internal ceramic, natural stone and mosaic wall tiling in normal conditions. Code of practice” — alongside BS 8000-11 for site workmanship. These are British Standards published by BSI. They are paid, copyrighted documents, not freely publishable text, in the same way AS 3740 is paywalled in Australia or DIN 18534 is in Germany. This page doesn’t quote figures from BS 5385-1 because we haven’t reproduced a standard we’d need to license.

New-build warranty providers add a second layer on top. NHBC Standards — a private technical rule book, not a statutory instrument — set out its own wet-area waterproofing detail for anything built to NHBC warranty, and other warranty bodies (Premier Guarantee, LABC Warranty and similar) run comparable private standards of their own. None of these are Building Regulations; they are contractual conditions of the warranty you’re building to.

Scotland and Northern Ireland run separate regimes — the Building Standards Technical Handbooks and Technical Booklet H respectively — not covered by this page. If the job isn’t in England or Wales, start from the UK building regulations hub and confirm which nation’s document actually applies before you rely on anything here.

What this means on site

Because there’s no code clause to build to, the job is to follow the standard and the product, not a page number:

1. Get a copy of BS 5385-1 (and BS 8000-11 for workmanship) if you’re pricing or detailing tanking work — through BSI or your trade body. Don’t rely on a secondhand summary for the actual design detail; the current edition is the one to work from.
2. If the build is going to NHBC (or another warranty body’s) standard, get that warranty provider’s current wet-area technical requirements — they can be stricter, or more specific, than BS 5385-1 alone.
3. Follow the membrane manufacturer’s instructions to the letter — coats, cure times, primer, upstand heights, tanking-to-drain detailing. The product data sheet and the manufacturer’s installation guide are what a building control surveyor or a warranty inspector will actually check against on site, in the absence of a Building Regs clause to point to.
4. Keep the paperwork. With no statutory clause to cite, your evidence of compliance is the standard you followed, the product data sheet, and a record that you installed it as specified — that’s what demonstrates “reasonable provision” if it’s ever questioned.

Related

• Part of the UK building regulations hub — how the devolved nations’ documents fit together.
• Building the room around it? See Does the UK have a minimum ceiling height? — another case where the Approved Documents are quieter than people expect.

Sources

• Approved Document C (2004 edition, incorporating 2010 and 2013 amendments), “Site preparation and resistance to contaminants and moisture” — confirmed by direct read to contain no bathroom, shower or wet-room clause; its scope is ground, wall and roof moisture. Read it at gov.uk.
• BS 5385-1:2018, “Wall and floor tiling — Part 1: Design and installation of internal ceramic, natural stone and mosaic wall tiling in normal conditions. Code of practice” — the standard that actually governs wet-room tanking detail in the UK. Published and sold by BSI; not reproduced here. See bsigroup.com.
• BS 8000-11, “Workmanship on building sites” (tiling section) — site workmanship standard, paired with BS 5385-1. Published by BSI.
• NHBC Standards — private technical requirements for NHBC-warranted new-build work, not a Building Regulation. See nhbc.co.uk.

Read this first. This page covers England and Wales, where Approved Document C applies. Scotland and Northern Ireland run their own building standards regimes with their own documents. BS 5385-1 and NHBC Standards are both paid/private publications — always confirm the current edition directly with BSI or the relevant warranty body before you rely on any detail from them. (Verified against Approved Document C as at 2026-07-31.)