Wet Room Regulations UK: Drainage, Ventilation, Electrics and Glass

There is no single set of wet room regulations in the UK. No Approved Document has a chapter called "wet rooms", and nothing in the Building Regulations tells you how to waterproof a floor. What applies instead is a handful of rules written for bathrooms in general, and a wet room happens to test every one of them at once: the drainage under Part H, the extract rate under Part F, the electrical special location under Part P, and safety glazing under Part K. Get those four right, add proper structural thinking about the floor, and the room is compliant.

Is a wet room building work at all?

Often, yes, even though nobody treats a bathroom refit as a building project. Replacing like for like on existing pipework and cabling generally needs no application. A wet room is rarely like for like. It usually means a new or relocated floor waste, new drainage runs to the stack, changes to the floor structure to create a fall, a new extractor, and new or altered circuits in the most sensitive electrical location in the house.

Some of that is plainly notifiable. Under regulation 12(6A), installing a new circuit or altering circuits in a special location is notifiable electrical work, which our Part P guide covers in full. Other elements, such as new drainage and structural changes to joists, bring the work within Parts H and A. If you are unsure whether your particular scheme needs an application, ask your local building control body before work starts; it is a short conversation and far cheaper than a retrospective regularisation.

In a flat, check the lease too. Moving a waste or cutting into a floor that forms part of the building's structure usually needs the freeholder's consent, and our guide to licences to alter explains how that works.

Drainage: Part H

This is where wet rooms go wrong most often, because the floor is the shower tray. Approved Document H sets out the minimums:

The reason for the seal depth is to stop foul air from the drain entering the room. Low-profile wet room gullies exist precisely because a deep trap is hard to fit into a timber floor, so check that the gully you choose states the seal depth it achieves, and that its flow rate keeps up with the shower head. A rainfall head delivers far more water than a standard one, and a gully that cannot clear it will flood the room even with a perfect fall.

Where the waste runs is a design decision, not a detail. A linear drain against a wall means the floor falls in one direction, which suits large-format tiles. A centre gully means falls in four directions and more cuts. Either way, the route from the gully to the stack has to fit the joists, which is where the structure comes in.

The floor: structure and falls

A wet room floor has to be rigid, and it has to fall to the waste. On a concrete ground floor that is a screed job. On a suspended timber floor, which describes most upstairs bathrooms in London houses, the options are a pre-formed sloping former laid between or over the joists, or lowering and packing the joists themselves. Any notching, cutting or lowering of joists changes a structural element, which falls under Part A of the Building Regulations. Get a structural engineer to specify it rather than relying on rules of thumb, particularly in a Victorian house where the joists may already have been cut by previous plumbers.

Deflection matters as much as strength. A floor that flexes slightly under a person's weight will crack grout and break the waterproof membrane at the joints, and the first sign is usually a ceiling stain in the room below. Stiffening the floor is not a regulation, it is the difference between a wet room that lasts and one that leaks.

Waterproofing: what the regulations do not say

The Building Regulations do not specify tanking for a domestic wet room. Waterproofing is covered instead by product manufacturers' installation instructions and by British Standards on tiling workmanship, and those are what a warranty or an insurer will read your installation against. In practice, a proper system means a waterproof membrane across the whole floor and up the walls, with sealed tapes at every wall and floor junction, and a gully with a clamping ring or flange designed to bond to that membrane. Using one manufacturer's system from gully to membrane to adhesive is the simplest way to keep the warranty intact.

Ventilation: Part F

A wet room produces more moisture in more places than a bathroom with a screen and tray, so ventilation is not optional. The minimum rates for a bathroom are 15 l/s for an intermittent extractor, or a minimum high rate of 8 l/s on a continuous system. Those are figures delivered at the grille, not the number on the fan's box, and a long flexible duct with bends will cut a fan's output well below its rating. Our extractor fan regulations guide has the full table and the commissioning points.

In a wet room it is worth going beyond the minimum: a humidistat or overrun timer keeps the fan running after the shower, which is what actually dries the floor, walls and grout.

Electrics: Part P and the special location

In a room containing a shower, the special location is the space around the shower head, extending vertically from the finished floor to 2.25 metres, or to the shower head if it is fixed higher. Inside that space, any addition or alteration to an existing circuit is notifiable, as is any new circuit anywhere. Approved Document P also notes that socket-outlets should not be located within 3m of a bath tub or shower tray.

A wet room complicates this because there is no tray to measure from. The water spreads across a wider area, and so should your thinking about where switches, sockets, shaver points, heated towel rails and electric underfloor heating go. Use a registered electrician who can self-certify, and plan the electrical layout before the membrane goes down, not after. Electric underfloor heating in a wet room is a new circuit in a special location; see our underfloor heating regulations guide.

Glass: Part K

Most wet rooms have a fixed glass panel instead of a door. Under Approved Document K, glazing between floor level and 800mm in a wall, and between floor level and 1500mm in a door or in a side panel within 300mm of a door edge, is in a critical location. Glass in those zones must break safely, be robust, or be permanently protected. Shower screens sold for the purpose are normally toughened safety glass, but check the marking, and take extra care with any glass that is part of a partition wall or a door into the room. Our safety glass guide explains the zones in detail.

Accessible wet rooms

Many people build a wet room so they can keep living in their home as they get older. If that is the aim, plan the space as well as the finish. The access zones in Approved Document M for WCs, basins and showers are a sensible design standard even where they are not a legal requirement, and our bathroom clearance dimensions guide sets them out. For a smaller room, see the minimum bathroom size guide before assuming a wet room will fit.

Frequently Asked Questions

Do you need building regulations approval for a wet room?

Often, for parts of the work. New circuits or alterations to circuits in the special location around the shower are notifiable under Part P, and new drainage and structural changes to the floor bring in Parts H and A. Replacing fittings like for like on existing pipes and cables is not normally notifiable. Check with building control before starting.

What size trap does a wet room shower need?

Approved Document H gives a minimum shower trap diameter of 40mm with a 50mm water seal. The seal may be reduced to not less than 38mm where the shower discharges directly to a gully, and every trap should keep at least 25mm of seal under working and test conditions.

Does a wet room need an extractor fan?

Yes. Part F sets a minimum extract rate for a bathroom of 15 l/s for an intermittent fan, or a minimum high rate of 8 l/s on a continuous system. The rate should be achieved at the grille, so allow for duct losses.

How far from the shower can sockets and switches go?

The special location extends from the floor to 2.25m around the shower head, and work on circuits there is notifiable. Approved Document P also says socket-outlets should not be located within 3m of a bath tub or shower tray. In a wet room without a tray, allow a wider margin and plan the layout with a registered electrician.

Is tanking a building regulations requirement for a wet room?

No. The Building Regulations do not specify how a domestic wet room is waterproofed. It is a workmanship and warranty matter, governed by the manufacturer's instructions for the membrane system and by British Standards on tiling, and a failed membrane is the most common cause of a leaking wet room.

Can you put a wet room upstairs?

Yes, but the timber floor has to be stiff enough not to flex, and forming the fall to the waste usually means a sloping former or altering the joists. Any change to the joists is structural work under Part A, so have a structural engineer specify it.

Sources

• Approved Document H: drainage and waste disposal, for Table 1 trap sizes and seal depths, and paragraphs 1.3, 1.15 and 1.16
• Approved Document F: ventilation, for bathroom extract rates
• Approved Document P: electrical safety, dwellings, for notifiable work and the special location dimensions
• Approved Document K: protection from falling, collision and impact, for critical glazing locations

Checked on 17 September 2026. This guide covers England. Building control bodies interpret notifiable work case by case; confirm your own scheme before starting. For a wet room designed around your home, see Vertigo Interiors.