Building Regulations are the one permission people forget, because they are not a permission. Planning is something you apply for. A licence to alter is something a freeholder grants. Building Regulations simply apply — to the work, as a matter of law, whether or not anyone asks, and whether or not you knew.
For bathrooms, three parts do most of the work: Part F for ventilation, Part G for sanitation and hot water, and Part P for the electrics. This page explains what each is doing and how it collides with the reality of a Central London flat. It is written from the site side and it is general guidance. For anything consequential, confirm the position with building control, an approved inspector, or your designer.
Part F: ventilation, and why it decides your layout
Bathrooms produce large volumes of water vapour in a small room. Without a means of removing it, that vapour condenses on the coldest surface available and you get mould, damaged decorations, and eventually damaged fabric. Part F deals with ventilation, and a bathroom is expected to have adequate extract.
The practical consequence in a flat is brutal in its simplicity: the air has to get out of the building. That means a duct, and a duct means a route, and a route means either an existing opening, a window, an existing duct or shaft, or a new hole in an external wall.
In Central London, that last option is frequently the one that is unavailable. If the building is listed, cutting a new terminal into the fabric may need listed building consent — see listed building consent for bathrooms. If it is in a conservation area, external changes are subject to additional planning controls, and flats generally have few permitted development rights to fall back on — see conservation area rules in Central London. And your lease will typically have something to say about penetrating the structure or altering the exterior at all — see freeholder consent for a bathroom refurbishment.
So a requirement that reads as a two-line technical point becomes the pivot of the whole project. Internal bathrooms — very common in mansion flats and conversions, where a bathroom was carved out of a corridor or a box room a century ago — are where this bites hardest. Solve the extract route before you choose a single fitting. Everything else is negotiable; physics is not.
Part G: sanitation, hot water and safety
Part G covers sanitation, hot water safety and water efficiency. In practical terms it is about the things that make a bathroom safe and sane: adequate sanitary provision, safe hot water, and the arrangements around unvented hot water systems.
The one worth flagging for owners is hot water. Unvented cylinders are a specific installation with specific competence requirements and specific safety provisions — discharge arrangements above all. This is not an area for improvisation, and it is not an area where a cheap price is a good sign. Anything involving a cylinder in a flat should be designed, installed and certified properly, and the discharge has to go somewhere legitimate rather than somewhere convenient.
Scald risk is the other. There are requirements around the temperature of hot water to baths, and thermostatic control is the usual answer. In a let property this is worth doing thoughtfully rather than minimally; you do not control who lives there or who visits.
Our plumbing work starts from £80, and the water side of a bathroom is where the long-term risk sits — see also our bathroom refurbishment page, where bathrooms start from £2,800.
Part P: electrics in a wet room
Electrical work in dwellings falls under Building Regulations Part P, and installations are to BS 7671, the wiring regulations. A bathroom is a special location under BS 7671 for the obvious reason: water and electricity share a room.
What that means on site is that where things may be installed, what protection is required, and how the space is zoned all follow rules rather than preference. Shaver sockets, heated mirrors, extract fans, underfloor heating, towel rails, lighting — each has a correct treatment and each is capable of being done wrong in a way that looks perfectly fine.
Certain electrical work is notifiable under Part P, which means it must either be carried out by someone registered under a competent person scheme who can self-certify, or notified to building control. Either way you should be handed certification at the end. Keep it. It is the only evidence the work was done properly, it will be asked for when you sell, and it makes the next EICR a shorter conversation. Landlords should read that alongside landlord electrical safety standards, and our electrical work starts from £80.
The parts nobody mentions
Part F, G and P are the headline three, but a bathroom can engage others depending on what you are doing — drainage and waste, fire safety where you penetrate a floor or ceiling, structure where you touch joists, and the provisions around energy and controls if heating or hot water is altered. We are not going to enumerate them here, because which apply depends entirely on the job, and getting that list right is what building control or an approved inspector is for. Ask them, not a website.
Why compliance and quality are not the same thing
It is worth being honest about the limits of regulation. Building Regulations set a minimum standard for health, safety and welfare. They are not a specification for a bathroom that will still be sound in fifteen years, and a compliant bathroom can still be a bad one.
The clearest example is waterproofing. What actually keeps water out of the flat below is the detailing — the tanking, the falls, the treatment of junctions and upstands, whether pipework was pressure-tested before it was covered, and whether isolation valves are somewhere a person can actually reach. Get those right and a bathroom is uneventful for years. Get them wrong and the first anyone knows is a stain on someone else's ceiling, by which point the tiling has to come off.
So use the regulations as the floor, not the target. When you compare quotes, compare the things that are not regulated as closely as the things that are: the build-up, the tanking system, the testing regime, and what happens when something needs attention in five years.
Approval routes
Where work requires it, there are routes for dealing with Building Regulations — through the local authority's building control service or through an approved inspector — and there is provision for regularising work carried out without approval, which is always more painful and more expensive than doing it in order. Some work is covered by self-certification through competent person schemes, which is why registered electricians and gas engineers matter.
Which route applies to your bathroom depends on the scope. A like-for-like replacement, a full strip-out and reconfiguration, and a new bathroom in a room that was not one are three genuinely different propositions. Ask before you assume.
Where the flat makes it harder
Everything above is national. The Central London part is the building.
- Shallow floor voids. Timber floors in mansion blocks were not built to accommodate a 100mm waste at a fall. This is the single most common design constraint in a flat bathroom, and it interacts with structure — see party wall agreements for flat refurbishment.
- Internal rooms. No external wall, no window, no obvious extract route.
- The flat below. Their ceiling is your floor. Waterproofing and pressure testing are not optional details.
- Old services. Lead, iron, and pipework of unknown provenance running through voids to places nobody remembers.
- Heritage fabric. Cornices, lath and plaster ceilings, original joinery — all of which interact with downlights, ducts and fixings.
- Access and hours. Porters, service lifts, restricted noisy working hours, no skip. Common across the blocks of St John's Wood, Maida Vale, Little Venice, Mayfair and Marylebone, and awkward in a different way in the lift-less converted terraces of Bayswater and Paddington.
Three systems that do not talk to each other
Say it plainly, because this is the thing that costs people months. Building Regulations compliance is not planning permission. Planning permission is not your freeholder's consent. Your freeholder's consent does not deliver Building Regulations compliance.
You can hold a licence to alter and still be building something non-compliant. You can build something entirely compliant and still be in breach of your lease. In a listed flat in a conservation area you may need all of them plus listed building consent — see licence to alter in a mansion block for how the lease side runs.
The order that works
- Establish the extract route. Genuinely first.
- Establish the waste route and the fall, and whether the void can take it.
- Then draw the layout. Not before.
- Establish the consents — lease, planning, heritage — and the Building Regulations route.
- Strip out and first fix, then test, then certify, then waterproof, then tile, then second fix.
- Keep every certificate with the deeds. Electrical, gas, unvented — all of it.
How we work
Set prices, a fixed quote before anything starts, and a specification that says what is going in rather than leaving it to the day. We would rather tell you at the quoting stage that the layout you want cannot be ventilated or drained than discover it once the floor is up. Bathrooms from £2,800; larger refurbishment quoted per project; ongoing maintenance for landlords and agents, with a service built around managing agents for portfolios.
Send drawings or photos through the quote form or on WhatsApp.
This page is general practical guidance and not a compliance assessment of your project. Requirements and approved documents are revised over time — confirm the current position with building control, an approved inspector, or your designer before relying on anything here.