In short: Almost never. Planning permission covers the outside of a building and how it is used, and a wet room is an internal alteration to a house that stays a house. The exceptions are listed buildings, where internal changes need listed building consent, and leasehold flats, where the lease usually requires the freeholder's consent. What a wet room does need is building regulations compliance — for the electrical work, the drainage, the ventilation, the structural work in the floor, and any accessibility requirements if the wet room is part of a funded adaptation — and that is where the real paperwork is.
What's in this guide 7 sections
01 Planning permission: the short answer
Planning permission is concerned with the external appearance of buildings, their size, and their use. Converting a bathroom into a wet room, turning a bedroom into a wet room, or fitting a wet room into an existing extension changes none of those, so in a normal house it needs no planning application at all. The same is true of most bathrooms, en suites and downstairs toilets.
You would need to think about planning only if the wet room is part of something bigger — an extension, a loft conversion with a dormer, a garage conversion in an area where permitted development rights have been removed — and then it is the extension that needs permission, not the wet room inside it.
02 The two exceptions
- Listed buildings. Internal alterations to a listed building need listed building consent from the local authority, and that includes removing walls, altering floors and changing original fittings. A wet room in a listed cottage is entirely possible but the application comes first, and the conservation officer will want to see how the floor and any original features are treated.
- Leasehold flats. Not planning as such, but most leases require the freeholder's written consent for alterations, and some prohibit changes to the floor construction or the position of bathrooms outright because of the flat below. Check the lease before the survey, not after the strip-out.
03 Building regulations: the long answer
The Building Regulations are a separate system from planning, and they apply to the work itself regardless of whether planning was needed. Several parts of them touch a wet room, and the sign-off for each comes either from the local authority's building control team, from a private approved inspector, or from a competent-person scheme that lets a registered tradesperson self-certify their own work.
| Element of the wet room | Regulation | What it requires | Who signs it off |
|---|---|---|---|
| Electrical work — lights, fan, shower, sockets | Part P | Work in a bathroom is notifiable; fittings must be rated for their zone | A Part P registered electrician self-certifies, or building control inspects |
| Extractor fan | Part F | Mechanical ventilation, normally 15 litres per second intermittent, ducted to outside | Electrician (Part P) or building control |
| Hot water | Part G | Thermostatic mixing to limit scalding; unvented cylinder work is notifiable | Plumber on a competent-person scheme, or building control |
| Drainage — new or moved waste and soil connections | Part H | Correct falls, traps, access and connection to the existing system | Building control, or a plumber on a competent-person scheme |
| Floor structure — notching joists, forming the fall | Part A | Joists must not be weakened beyond the permitted limits | Building control |
| Level-access wet room for a disabled person | Part M | Where it is a funded adaptation, the layout and fittings follow Part M and the occupational therapist's specification | Building control, with the council's adaptations team |
Waterproofing — the tanking membrane behind the tiles — is not itself a building regulation, which is a large part of why so many wet rooms leak. It is the single most important part of the job and it is enforced by nobody but the fitter.
04 The floor is where the structural question lives
A wet room needs a fall to the drain, and on a timber floor that is formed either with a pre-formed tray set between or on top of the joists, or by building the floor up. Where the tray sits between joists, the joists may need notching or trimming for the waste and the tray, and that is where building control takes an interest: joists can only be notched within set limits of depth and position before they are weakened. A wet room former with a shallow waste and the drain positioned to run parallel with the joists avoids most of the problem, and it is the kind of thing that is decided at the survey rather than discovered under the floorboards.
On a solid concrete ground floor the question is different: the drain has to be cut in and connected, which is a Part H matter, and the fall has to be formed in screed or a former on top. It is more disruptive but structurally simpler.
05 Building notice or full plans?
For a domestic wet room, where building control needs to be involved at all, a building notice is the usual route: you tell the council the work is starting, pay the fee, and an inspector visits at the stages that matter — usually the drainage before it is covered and the floor before it is boarded. Full plans are for larger projects. Where the electrics and plumbing are done by registered tradespeople under competent-person schemes, they notify their own work and a certificate arrives in the post; if all of the notifiable elements are covered that way and the floor is not being altered structurally, a separate building control application may not be needed at all. Your fitter should be able to tell you which applies before the job starts, not after.
The local authority for building control is Bolsover, Bassetlaw, Mansfield, Chesterfield, Ashfield, North East Derbyshire, Rotherham or Newark & Sherwood depending on where the house sits. Fees and turnaround vary a little between them.
06 Funded adaptations: the Disabled Facilities Grant
If the wet room is being fitted because someone in the house has a disability or limited mobility, it may qualify for a Disabled Facilities Grant through the local council. The route is an assessment by an occupational therapist, who specifies what is needed — level access, a fold-down seat, grab rails, a thermostatic shower at a set height — and the council then funds the work, in part or in full, subject to a means test for adults. The specification becomes the building brief, Part M applies, and the council's own surveyor inspects. It takes longer than a private job, but for the right household it is worth the wait.
07 What to ask your fitter before you start
- Who is certifying the electrical work, and are they Part P registered?
- Is the drainage being altered, and is building control being notified?
- Will any joists be notched or cut, and who has checked the limits?
- What is the tanking system, and does it go up the walls as well as across the floor?
- Will you give me the certificates and completion notices at handover? You will need them when you sell.