Extensions over a garage in St James's
If you live in St James's and need more room without moving, an extension over a garage is worth a serious look. We handle the drawings, approvals, structure and build.
Quick reference for homeowners in St James's.
- Postcode districts
- SW1Y, W1J, W1K and W1S
- County / area
- Greater London, England
- Price region
- London
- Guide price
- £38,000–£55,000 (£2,100–£3,060 per m²)
- Approval route
- Planning permission is needed: in England, permitted development only allows single-storey extensions to the side.
- Nearest towns
- Soho (0.5 miles), Westminster (0.7 miles), Holborn (1.1 miles)
- First visit
- Free, no obligation
About an extension over a garage
An extension over a garage suits you if you have an attached single garage beside the house and need an extra bedroom or a larger main bedroom with an en-suite. You get an inspection of the garage structure, a design that matches the house, the approvals your nation needs, structural design, building regulations approval and the build, carried out by vetted teams working under S&K.
Around St James's we also work in Soho, Westminster and Holborn, and across the rest of Greater London. Postcode districts in and near St James's: SW1Y, W1J, W1K and W1S.
What it costs in St James's
Most of the cost of an extension over a garage is set by its size and specification. For St James's and the rest of London, our guide is £2,100–£3,060 per m² including VAT, so about £38,000–£55,000 for 3 m × 6 m of new first-floor space (18 m²). We'll give you a written design-stage price first, then a fixed build price once the drawings are agreed.
| Spec | Per m² | 3 m × 6 m of new first-floor space (18 m²) |
|---|---|---|
| Essential | £1,930–£2,820 per m² | £35,000–£50,500 |
| Standard | £2,100–£3,060 per m² | £38,000–£55,000 |
| Premium | £2,520–£3,670 per m² | £45,500–£66,000 |
Planning and building regulations in St James's
In England, most garages sit beside the house, so building over one makes a two-storey extension beyond a side wall, which always needs planning permission. If the garage is at the rear, the 3 m and 7 m rules for two-storey rear extensions apply, measured from the original house. A householder application costs £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 St James's homes
Checking the garage foundations
Garages are often built on shallow strip footings sized for a single-storey wall and a light roof. A trial hole shows their depth and condition, and the engineer decides whether they can carry two storeys or need underpinning or new foundations inside the garage.
Floor levels and headroom
Garage floors are often lower than the house, and the new first floor may not line up with the existing landing. We set the floor level to avoid awkward steps upstairs, while keeping enough headroom in the garage below for a car or storage.
How we'd run your project
Measure and listen
A visit to St James's to understand how you live in the house now and what the extra rooms need to do, plus a first look at the structure.
Design and approvals
We draw the extension and check it against the rules for England, then apply for planning permission or a certificate of lawfulness, whichever fits.
Engineer it
Foundations sized for two floors, steels for any openings, and building control approval, all before anyone starts on site.
Build and hand over
We manage the build from groundworks to decoration-ready finish and hand over with the completion paperwork.
Questions about extensions over a garage in St James's
How long does an extension over a garage take?
Allow 4 to 8 weeks for survey and design, then the approval period (councils should decide householder applications within 8 weeks of validation), then 4 to 8 weeks of technical design, which can overlap. The build itself usually takes 14 to 20 weeks, longer for large or complex designs.
Who handles building regulations for a project in St James's?
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 St James's?
We cover St James's (SW1Y, W1J, W1K and W1S) and nearby places including Soho, Westminster and Holborn, plus the rest of Greater London. The first site visit is free.
How do I get into a room over the garage?
Usually through a new opening off the existing landing or a bedroom, so the stairs stay where they are. If the floor levels do not match, a step or two may be needed inside the new room. Where a landing opening is not practical, a new stair from a converted garage is an option.
Can I add an en-suite above the garage?
Yes, and it is a common choice for a main bedroom. The en-suite needs an extract fan under Part F, a route for the soil pipe down to the drains and enough fall for the waste, which can be harder over a garage. We plan the pipe route through the garage or an outside wall early.
Nearby
We also cover places near St James's, including:
Other extensions in St James's
- Rear
- Side
- Wraparound
- Part two-storey
- First floor
- Semi-detached
- Detached
- Kitchen and bedrooms
- Bedroom and en-suite
All two-storey extension services in St James's · Extensions over a garage across Greater London
Want a figure first? Try our guide price tool, then book a free visit to firm it up.