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What does tanking mean in building work?

Tanking means applying a continuous waterproof barrier to walls and floors so water cannot get through, most often in basements and cellars below ground level. In bathrooms the same word is used for the waterproof layer behind shower tiles.

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By the QuoteZila editorial team. Editorial policy.

What is tanking?

Tanking is a way of waterproofing a part of a building by covering its walls and floor with a continuous barrier, like the inside of a tank. Water on the other side is held back and cannot soak through into the room.

The word is used in two main places:

  • Below ground. Basements, cellars and walls that have soil against them, where ground water can push against the wall.
  • In bathrooms. The waterproof layer applied behind tiles in showers and wet rooms.

The idea is the same in both: one unbroken barrier, sealed at every corner, joint and opening. The products and the risks are different.

Our damp proofing page covers the specialists who deal with walls below ground. QuoteZila starts in Cheshire, with Crewe, Nantwich and Sandbach first, and anyone in the UK can post a tanking job.

How does tanking work below ground?

A wall with soil against it can be wet for much of the year. If the water level in the ground rises, water can be pushed against the wall and floor. Approved Document C, the official guidance on resisting moisture, refers to BS 8102, the code of practice for protecting structures against water from the ground, for walls subject to groundwater pressure including basement walls [S1].

Tanking below ground is usually one of these:

  • Cementitious coatings. Special waterproof renders or slurries applied in coats to the inside of the walls and over the floor.
  • Bonded membranes. Sheets or liquids bonded to the wall that form a waterproof skin.
  • Combined with drainage. Some basements use a drained cavity system instead of, or as well as, a barrier, with a membrane that leads water to a sump and pump.

Which approach suits depends on how wet the ground is, what the basement will be used for, and the state of the walls. A specialist should survey before recommending one.

How is tanking different from a damp-proof course?

A damp-proof course (DPC) is a thin layer built into a wall near the bottom, to stop moisture rising up from the ground. Planning Portal says in external walls they are installed at least 150mm above ground level [S2]. Planning Portal also says installing or replacing a DPC in most instances does not need building regulations approval [S2], and is unlikely to need planning permission [S3].

Tanking is a barrier over the whole face of a wall or floor, usually where the room is partly or fully below the ground outside. A DPC cannot help a cellar wall that has soil against it from floor to ceiling, because the damp is coming through the face of the wall, not up from below.

Planning Portal says that in a listed building, installing damp proofing will typically need listed building consent [S3]. If your house is listed, speak to the council before any tanking or damp work.

What does tanking mean in a bathroom?

In a bathroom, tanking is the waterproof layer applied to walls and floors before tiling. It may be a liquid coating, a sheet membrane or a waterproof board system. The aim is to stop water that gets through grout or silicone from soaking the wall or floor behind.

Bathroom tanking does not deal with ground water at all. It is about water from the shower. Our shower waterproofing membrane guide explains the bathroom side in more detail.

When is tanking the wrong answer?

Tanking is not a cure for every damp wall. Before anyone tanks a wall, the cause of the damp needs finding.

GOV.UK lists condensation, penetrating, rising and traumatic damp as different types, and says traumatic damp can be caused by leaking pipes, overflowing baths or sinks and burst pipes [S4]. It says condensation is one of the most common causes of damp and mould in homes [S4]. A barrier on the wall does nothing for moisture in the room air, and it can hide a leaking pipe or gutter that should be fixed.

Ask any specialist:

  • What is causing the damp, and how did you find out?
  • Why do you recommend tanking rather than another fix?
  • What happens to the water held back by the barrier?
  • What guarantee do you give, in writing, and who backs it?

Jobs you might post

These are examples, not taken from real job posts.

  • "Cellar under a Victorian terrace, damp walls and puddles after heavy rain. Please survey and quote to make it usable for storage."
  • "Want to turn a damp basement into a playroom. Please advise on tanking or a drained system and quote."
  • "Shower enclosure needs tanking before retiling. Please quote for waterproofing and tiling."

QuoteZila is free for customers and local businesses [QZ1]. Your job goes to up to five matched local businesses [QZ2].

Honest status: QuoteZila is new. We're starting in Cheshire, beginning with Crewe, Nantwich and Sandbach, and growing area by area. Anyone in the UK can still post a job or register a business. How fast you get quotes depends on how many local businesses have joined near you. Businesses can register and receive jobs straight away. We don't check insurance, qualifications or registrations, so please check these yourself before you hire.

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Questions about tanking

Is tanking the same as damp proofing?

Not quite. A damp-proof course is a thin layer low down in a wall that stops moisture rising. Tanking is a barrier over a whole wall or floor that holds back water, often under pressure from the ground. Both deal with damp, in different places.

Does tanking stop condensation?

No. Tanking stops water coming through a wall or floor. Condensation forms from moisture in the air inside the room. GOV.UK says condensation is one of the most common causes of damp and mould in homes, and it needs ventilation and heating rather than tanking.

Who does tanking work?

Basement and cellar tanking is usually done by damp proofing and waterproofing specialists or builders. Shower and wet room tanking is usually done by tilers or bathroom fitters as part of the job.

Does QuoteZila check damp proofing firms?

No. We don't check insurance, qualifications or registrations, so please check these yourself before you hire. You can report a quote or a business from your job page.

This page is general information, not professional or legal advice. QuoteZila does not check Gas Safe, WaterSafe, NFRC, NICEIC or other registrations against the register on your behalf: look them up yourself.

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Sources

  1. QZ1: QuoteZila product fact. QuoteZila home and FAQ copy.
  2. QZ2: QuoteZila product fact. QuoteZila FAQ How does getting quotes work.
  3. S1: Approved Document C: Site preparation and resistance to contaminants and moisture (2013 edition), GOV.UK (MHCLG). Accessed 2026-11-02. https://assets.publishing.service.gov.uk/media/5a8192a0e5274a2e8ab54b5f/BR_PDF_AD_C_2013.pdf
  4. S2: Damp proofing: Building regulations, Planning Portal. Accessed 2026-11-02. https://www.planningportal.co.uk/permission/common-projects/damp-proofing/building-regulations
  5. S3: Damp proofing: Planning permission, Planning Portal. Accessed 2026-11-02. https://www.planningportal.co.uk/permission/common-projects/damp-proofing/planning-permission
  6. S4: Understanding and addressing the health risks of damp and mould in the home, GOV.UK (DHSC and MHCLG). Accessed 2026-11-02. https://www.gov.uk/government/publications/damp-and-mould-understanding-and-addressing-the-health-risks-for-rented-housing-providers/understanding-and-addressing-the-health-risks-of-damp-and-mould-in-the-home--2