Extra bedroom and en-suite extensions in Belsize Park
Want to stay in Belsize Park but need more space? An extra bedroom and en-suite extension adds floor area on two levels without giving up much garden. Here's what's involved.
What we'd confirm first for a project in Belsize Park.
- Postcode districts
- NW3
- County / area
- Greater London, England
- Price region
- London
- Guide price
- £67,000–£90,500 (£2,400–£3,240 per m²), plus £5,500–£11,000 for the en-suite
- Approval route
- It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission.
- Nearest towns
- Hampstead (0.6 miles), Kilburn (0.9 miles), Chalk Farm (1 mile)
- First visit
- Free, no obligation
About an extra bedroom and en-suite extension
This service suits you if you need another bedroom, or want a main bedroom with its own bathroom, without converting the loft or moving. You get a first-floor layout that connects well to your landing, an en-suite designed for plumbing and ventilation, a useful room downstairs, the approvals your nation needs and the build, managed by us and carried out by vetted teams working under S&K.
We cover postcode district NW3 in and around Belsize Park, along with neighbouring Hampstead, Kilburn and Chalk Farm.
What it costs in Belsize Park
In London, which includes Belsize Park, we'd expect an extra bedroom and en-suite extension to cost around £67,000–£90,500 (plus £5,500–£11,000 for the en-suite) for a 4 m × 3.5 m footprint on two floors (28 m² of new floor space), or £2,400–£3,240 per m² including VAT. The fastest way to a firmer number is a free site visit, after which we price the design stage in writing.
| Spec | Per m² | A 4 m × 3.5 m footprint on two floors (28 m² of new floor space) |
|---|---|---|
| Essential | £2,210–£2,980 per m² | £62,000–£83,500 |
| Standard | £2,400–£3,240 per m² | £67,000–£90,500 |
| Premium | £2,880–£3,890 per m² | £80,500–£109,000 |
Planning and building regulations in Belsize Park
In England, an extra bedroom extension at the rear can be permitted development if it goes no more than 3 m beyond the original rear wall and stays 7 m from the rear boundary. Upper side windows, including en-suite windows, must be obscure-glazed and non-opening below 1.7 m. Side or deeper designs need planning permission, costing £548 (or £575 for applications made from 8 December 2026).
Approval in England: Householder planning application: £548 (or £575 for applications made from 8 December 2026). Lawful development certificate: £274 (about £288 for applications from 8 December 2026). Councils should decide householder applications within 8 weeks of validation.
Building regulations: Building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end.
Design points for Belsize Park homes
Sound and privacy
Bedrooms above a kitchen or family room benefit from an insulated floor to reduce noise. Side-facing upstairs windows usually have to be obscure-glazed, so we place the main bedroom window to the rear and the en-suite window to the side where possible.
Planning the en-suite
An en-suite needs a route for the soil pipe to the drains, enough fall for waste water and an extract fan to the outside under Part F. Placing it over the ground-floor utility or near an existing drain keeps pipework short and hidden.
How we'd run your project
Measure and listen
A visit to Belsize Park to understand how you live in the house now and what the extra rooms need to do, plus a first look at the structure.
Drawings, then consent
We draw the scheme, check it against the rules in England, and take it through the right consent with the council.
Technical design
We prepare the building regulations drawings, structural calculations and specification so the build price can be fixed.
Build it
The new structure goes up first, then we open into the house, finish inside and get the completion certificate.
Questions about extra bedroom and en-suite extensions in Belsize Park
Who handles building regulations for a project in Belsize Park?
We handle it as part of the project. What's needed in England: building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end. We prepare the drawings and the engineer's calculations, book the inspections and pass you the completion paperwork at the end.
Which postcodes do you cover around Belsize Park?
We cover Belsize Park (NW3) and nearby places including Hampstead, Kilburn and Chalk Farm, plus the rest of Greater London. The first site visit is free.
Do I need planning permission for an extra bedroom and en-suite extension in Belsize Park?
Belsize Park is in England, so England planning rules apply. It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.
Can an en-suite go in a room with no window?
Yes. A shower room without a window is allowed, provided it has a mechanical extract fan to the outside that meets Part F. Many people prefer a window for daylight, but if it faces a neighbour it will usually need obscure glass. We plan the extract route early so the duct is hidden.
What goes on the ground floor below a new bedroom?
Whatever suits you: a bigger kitchen, a family room, a study, a utility or a downstairs shower room. The ground floor usually costs about the same whatever it is used for, apart from kitchen units and bathroom fittings, which are priced separately.
Nearby
Close to Belsize Park? We work across the area, including:
Other extensions in Belsize Park
All two-storey extension services in Belsize Park · Extra bedroom and en-suite extensions across Greater London
Want a figure first? Try our guide price tool, then book a free visit to firm it up.