The short answer
Waterproofing (tanking) and the right floor build-up are the hidden parts of a bathroom that keep water out of the structure. Wet zones need a waterproof membrane behind the tiles; floors need a stable, water-resistant substrate; and a full wet room needs the whole floor tanked and graded to a drain. Skimping here is the most expensive mistake you can make. See our wet room cost guide for the fully tanked case.
The parts of a bathroom that protect your home are the parts you never see once it is finished. This guide explains waterproofing and flooring — what tanking is, where it is needed, what goes under the tiles, and which floor finishes suit a bathroom — so you can recognise a quote that includes the work that matters.
Flooring & waterproofing at a glance
- Tanking Waterproof membrane in wet zones
- Backer board Stable, water-resistant tile base
- Wet room Whole floor tanked + graded to drain
- Floor options Tile, LVT, sheet vinyl
- Underfloor heating Optional; adds Part P electrics
- Key rule Never skip waterproofing
What waterproofing (tanking) is
Tanking is the application of a waterproof barrier — a liquid-applied membrane or a sheet system — over the substrate before tiling, so that any water passing through grout lines or tile joints cannot reach the wall or floor structure. In a standard bathroom, tanking is concentrated in the wet zones: the shower enclosure walls and floor, and around the bath. In a wet room, the whole floor and the lower walls are tanked because the entire area gets wet. Joints, corners and pipe penetrations are sealed with matching tape and collars. Because the membrane is covered by tiles, its quality cannot be judged afterwards — which is exactly why it has to be done correctly the first time.
What goes under the tiles
Tiles need a flat, sound, stable base. On masonry walls this may be plaster or render; in wet areas, tile-backer board (a water-resistant board) is often used to give a stable, moisture-tolerant substrate. Floors need particular attention: a solid floor must be sound and level, while a suspended timber floor may need overboarding or a decoupling layer to handle movement so tiles do not crack. Getting the substrate right is part of the tiling preparation covered in our tiling cost guide — and it is where rushed jobs cut corners.
| Floor finish | Strengths | Considerations |
|---|---|---|
| Ceramic / porcelain tile | Durable, fully waterproof surface | Cold underfoot unless heated; needs solid base |
| Luxury vinyl tile (LVT) | Warm, comfortable, water-resistant | Quality and fitting vary; edges must be sealed |
| Sheet vinyl | Seamless, very water-resistant, economical | Less premium look; joints must be welded |
| Natural stone | Premium appearance | Needs sealing; heavier; higher cost |
Wet rooms and drainage
A wet room takes waterproofing furthest: the whole floor is tanked and graded so water falls to a central or linear drain, usually using a proprietary former or a graded screed. The drainage must be connected with the correct falls. This is the work that makes a wet room more expensive and more demanding than a standard bathroom — covered in detail in our wet room cost guide. Upper-floor wet rooms need especially careful detailing because a failure damages the rooms below.
Underfloor heating and ventilation
Underfloor heating — an electric mat or a wet system under the floor finish — is a popular bathroom upgrade that takes the chill off tiles. An electric system adds notifiable work under Part P. Whatever the floor, good ventilation keeps moisture from accumulating and protects the finishes; our ventilation and damp guide covers the Part F requirements. Together, proper waterproofing, a sound substrate and adequate ventilation are what make a bathroom last. This page is general information; the right specification depends on your room and floor structure.
Compare bathroom quotes
Use our service to compare itemised quotes from a bathroom installation specialist who specifies the waterproofing and floor build-up properly.
Frequently asked questions
Does a standard bathroom need tanking?
The wet zones do — the shower enclosure and the area around the bath should be waterproofed behind the tiles. A full wet room needs the entire floor and lower walls tanked. Tanking protects the structure from water passing through grout and joints.
What is the best flooring for a bathroom?
Tile and porcelain give a durable, fully waterproof surface; luxury vinyl tile and sheet vinyl are warmer and water-resistant; stone is premium but needs sealing. The best choice depends on budget, the look you want and whether you add underfloor heating.
Can I tile straight onto a timber floor?
Not usually without preparation. Suspended timber floors move, so they often need overboarding or a decoupling layer so the tiles do not crack. Getting the substrate right is part of proper tiling preparation.
Is underfloor heating worth it in a bathroom?
Many people value it for taking the chill off tiled floors. An electric system is straightforward to add during a refit but involves notifiable electrical work under Part P, so it should be installed and certified by a competent person.
Sources & further reading
- CIPHE — plumbing and wet-area installation standards
- KBSA — consumer guidance on bathroom finishes
- GOV.UK / Building Regulations Approved Documents P and F — electrics and ventilation
- TrustMark — finding a vetted tradesperson for home improvement work
This is general information, not advice for your specific property or installation. The right specification varies with your room and floor structure. Bathroom Answers is an independent information and introduction service, not an installer.