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En Suite Building Regulations UK: Fans, Drains, Electrics and Who Signs It Off

En suite building regulations apply as soon as you create a new bathroom where there was none before, because an en suite brings new drainage, a new extract fan and almost always new electrical work. Swapping a tired toilet or basin in an existing bathroom does not need approval. This page goes through the rules in the order a builder meets them: approval, ventilation, electrics, drainage and layout, then hot water. It covers England; Wales and Scotland have similar rules with their own guidance.

Does a new en suite need building regulations approval?

Almost always. Replacing a basin, toilet or shower in an existing bathroom in the same position is a repair and does not need approval. Creating an en suite where there was none is different, because it adds new drainage connections, an extract fan and in most cases new electrical work. Those are controlled under the Building Regulations 2010, so you either submit a building notice or full plans application to your local authority, or use a registered building control approver.

Some parts can be self-certified. A registered electrician notifies their own work, a Gas Safe engineer notifies any gas work, and a competent person scheme installer can certify a fan or other notifiable work they carry out. Building control still needs to see the drainage and any structural work, and at the end you should hold a completion certificate. Without it, the work can come up when you sell; our page on regularisation certificates explains how unapproved work is put right after the event.

Planning permission is a separate question. Internal alterations to a house rarely need it, but a listed building needs listed building consent for almost any change, and a leasehold flat usually needs the freeholder's licence to alter. See licence to alter and listed building interior alterations.

Ventilation: the fan rules

An en suite with a shower or bath is a bathroom for ventilation purposes. Approved Document F sets a minimum extract rate of 15 litres a second for an intermittent fan, or 8 litres a second for a fan that runs continuously at a low rate. An openable window on its own does not meet the requirement for a new bathroom.

Many en suites are internal rooms with no window. In that case the fan should run on for 15 minutes after the light is switched off, and the room needs a way for replacement air to get in, usually a 10mm gap under the door. Duct the fan to outside, not into the loft, and keep the duct run short: a long or kinked flexible duct can cut a fan's real output well below its rating. Our extractor fan regulations page has the full table for every room.

Electrics: zones and Part P

A room containing a bath or shower is a special location under the wiring regulations. In England, Part P makes three kinds of electrical work notifiable: a new circuit, a replacement consumer unit, and additions or alterations to circuits in a special location. A new en suite usually involves at least one of these, so use an electrician registered with a competent person scheme, who will notify the work and give you a certificate.

Every circuit serving the room needs 30mA RCD protection. Light fittings, shaver sockets, heated towel rails and underfloor heating each have to suit the zone they sit in, and ordinary 13A sockets must be at least 2.5 metres from the edge of the shower or bath zone. The details are on our bathroom zones page.

Drainage and the macerator rule

Drainage is where most en suite plans succeed or fail. The toilet needs a route to the soil stack with enough fall, and the shower and basin wastes need their own runs. Approved Document H sets out pipe sizes and maximum lengths for unvented branches; as a guide:

Where a gravity route is impossible, a macerator and pump can carry waste through small-bore pipe. Approved Document G allows a WC fitted with a macerator only if there is also access to a WC that discharges directly to a gravity system, and the unit must meet BS EN 12050-1 or 12050-3. In practice that means an en suite can use a macerator as long as the main bathroom or a downstairs toilet does not. Plan for the noise, a power supply in the right zone, and access for servicing.

Running pipes across a bedroom floor often means cutting joists. Approved Document A guidance limits notches to an eighth of the joist depth, positioned between 0.07 and 0.25 of the span from a support, and holes to a quarter of the depth, drilled on the centre line between 0.25 and 0.4 of the span. Anything beyond that needs an engineer.

Basins, layout and separation from kitchens

Approved Document G says every room containing a WC needs a washbasin in the same room or in an adjacent space that is the only way into the WC, as long as that space is not used to prepare food. An en suite with a toilet and basin together meets that easily. A WC must also be separated by a door from any kitchen or food preparation area, which matters if you are carving an en suite out of space next to a kitchen in a flat.

There is no legal minimum size for an en suite, but there are practical ones. Our minimum bathroom size and bathroom clearance pages set out the space a toilet, basin and shower each need to be usable.

Hot water and the 48C bath limit

Requirement G3(4) limits the hot water to a new bath to 48C, usually with a thermostatic mixing valve. It applies only when a dwelling is newly built or formed by a material change of use, so a bath fitted in an en suite in an existing house is not caught by it. A thermostatic shower valve is still sensible in any en suite, especially for children or older relatives. If the new en suite means a new or larger hot water cylinder, that is separately notifiable; see unvented cylinder regulations.

Wet rooms, loft en suites and flats

• Wet room en suites need the floor tanked and laid to falls; see our wet room regulations guide.
• Loft conversions bring in fire safety, stairs and structure as well; the en suite is one part of a larger application. See loft conversion building regulations.
• Flats raise sound and leak risk for the neighbours below. Your lease, not just building regulations, may set conditions on where wet rooms can go.

An en suite is a room we design often in London homes, from compact shower rooms in Victorian terraces to full bathrooms in new loft storeys. Talk to Vertigo Interiors if you want the layout and the approvals planned together.

Sources: Approved Document G (2015 edition with 2016 and 2024 amendments, paragraphs 4.10, 4.11 and 4.25, and requirement G3(4)); Approved Documents A, F, H and P (GOV.UK); BS 7671. This page is general guidance for England; check with your building control body for your project.