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

The requirement

Approved Document C sets no wet-area tanking rule at all. There is no clause for a shower wall, a wet-room floor, or a bath upstand. The real detail lives in BS 5385-1:2018 and your membrane maker’s guide. That standard is paid, so this page names it but does not quote it.

So what does Approved Document C do? It is the guidance for Part C of the Building Regulations 2010. It deals with the shell of the building. Ground damp and contaminants under the slab. Damp coming through the outside walls. Rain getting past the roof. It never steps inside to the bathroom.

Looking for a shower-wall height or a membrane spec in there? You will not find one. Codes like Australia’s NCC or the US IRC do print those rules. Approved Document C does not. The gap is real. You have not missed the right page.

So someone tells you “the regs” set a height for tanking a shower wall in England or Wales. That number is not from Approved Document C. It comes from a standard. This page can name that standard. It cannot copy from it.

Where the actual numbers live

UK tanking work runs on BS 5385-1:2018. That is the British Standard for wall and floor tiling inside a building. BS 8000-11 sits with it and covers site workmanship. Both come from BSI. Both are paid and copyrighted. It is the same deal as AS 3740 in Australia and DIN 18534 in Germany. This page does not reprint a standard it would need to license.

New-build warranty adds a second layer. NHBC Standards is a private rule book, not law. It sets its own wet-area tanking detail for homes built under NHBC warranty. Premier Guarantee, LABC Warranty and other warranty bodies run their own private rule books too. None of these are Building Regulations. They are terms of the warranty you are building to.

Scotland and Northern Ireland run their own rules. Scotland uses the Building Standards Technical Handbooks. Northern Ireland uses Technical Booklet H. This page does not cover them. Job outside England or Wales? Start at the UK building regulations hub and check which nation’s rules apply first.

What this means on site

No code clause means you build to the standard and the product. Not to a page number. Here is the drill:

1. Get a copy of BS 5385-1 if you price or detail tanking work. Get BS 8000-11 for workmanship too. Buy them through BSI or your trade body. Work from the current edition. Do not trust a secondhand summary for the design detail.
2. Building to NHBC or another warranty body’s standard? Get that body’s current wet-area rules too. They can be stricter than BS 5385-1 alone. They can also be more exact.
3. Follow the membrane maker’s guide to the letter. Coats, cure times, primer, upstand heights, and the tanking-to-drain detail. There is no Building Regs clause to point to. So the building control surveyor or warranty inspector checks your work against the product guide instead.
4. Keep the paperwork. Your proof is the standard you followed, the product data sheet, and a record that you fitted it as specified. That is what shows “reasonable provision” if anyone asks later.

Related

• Part of the UK building regulations hub. It shows how the four nations’ rule books fit.
• Building the room around it? See Does the UK have a minimum ceiling height?. That is one more spot where the rules say less 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.)