Extensions Over a Garage: Build a Room Above

What you get

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.

It suits you if…

You have an attached garage beside the house with a flat or low-pitched roof
You need one more bedroom, an en-suite or a home office upstairs
You want to keep all of your garden
You want to keep the garage for parking or storage, or convert it at the same time

Line drawing: existing house in outline, new work in brick, blue dashed line at first-floor level.

Design points that matter

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.

Garage walls and the door opening

Garage walls are often a single skin of brick or block with piers, and the wide door opening needs a beam over it. Many over-garage extensions need new inner walls or a steel frame to carry the floor and to insulate properly, which we confirm before the design is fixed.

Fire separation

If the garage stays a garage, the floor between it and the room above, and any door into the house, must give fire separation under building regulations. That usually means fire-resisting plasterboard ceilings, sealed gaps and a fire door, which we design in from the start.

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.

Matching the house

A room over a garage usually sits beside the front of the house in full view, so roof form, ridge height, windows and brick matter. Setting the front wall and ridge back slightly from the main house usually helps it look as if it belongs.

Planning and approvals by nation

England

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.

Wales

In Wales, building over a side garage can be permitted development if the result is at least 10.5 m from the boundary opposite the side wall, set back at least 1 m from the front of the house and does not widen the house by more than 50%. Garages close to the boundary usually fail these tests, so a householder application costing £585 is often needed.

Approval in Wales: Householder planning application: £585. Councils normally decide householder applications within 8 weeks.

Building regulations: Building regulations approval under the Welsh Approved Documents, which differ from England's in places (notably energy efficiency).

Scotland

In Scotland, a room over a garage makes the extension more than one storey, so Class 1B applies, which needs at least 10 m to every boundary for permitted development. Attached garages are rarely that far from the boundary, so expect a householder application (£371, decided within two months) and a building warrant.

Approval in Scotland: Householder planning application: £371. Councils have two months to decide a local planning application.

Building standards: A building warrant from the council's building standards service before work starts, and a completion certificate at the end. Scotland uses its own Technical Handbooks.

Northern Ireland

In Northern Ireland, permitted development for two-storey work is set out for rear extensions, so building over a side garage normally needs a planning application, which costs £347 per dwelling. Councils aim for an average of 15 weeks for local applications. Building control approval is also needed, including fire separation if the garage stays in use.

Approval in Northern Ireland: Planning application for works to a house: £347. Councils aim to decide local applications within an average of 15 weeks; many take longer.

Building control: Building control approval from the local council under the Building Regulations (Northern Ireland), using the Technical Booklets.

Guide price

As a guide, an extension over a garage costs £31,500–£46,000 including VAT at 20% for 3 m × 6 m of new first-floor space (18 m²), based on West Midlands prices and our Standard spec; London and the South East are higher.

Guide prices by region
Region	Per m² of new floor	Typical project
London	£2,100–£3,060 per m²	£38,000–£55,000
South East England	£1,930–£2,800 per m²	£34,500–£50,500
East of England	£1,800–£2,630 per m²	£32,500–£47,500
South West England	£1,800–£2,630 per m²	£32,500–£47,500
West Midlands	£1,750–£2,550 per m²	£31,500–£46,000
East Midlands	£1,720–£2,500 per m²	£31,000–£45,000
North West England	£1,660–£2,420 per m²	£30,000–£43,500
Yorkshire and the Humber	£1,610–£2,350 per m²	£29,000–£42,000
North East England	£1,580–£2,300 per m²	£28,500–£41,500
Wales	£1,610–£2,350 per m²	£29,000–£42,000
Scotland	£1,640–£2,400 per m²	£29,500–£43,000
Northern Ireland	£1,540–£2,240 per m²	£27,500–£40,500

Typical project: 3 m × 6 m of new first-floor space (18 m²). Including VAT at 20%, Standard spec. Essential spec is about 8% less, Premium about 20% more. See all prices and fees or work out your own guide price.

What's included

Free site visit, including a first look at the garage
Trial hole and structural assessment
Design that matches the house
Planning application or permitted development check
Foundation, wall and beam design
Fire separation and building regulations approval
The build, carried out by vetted teams working under S&K

How it works

Free site visit
We look at your house, the boundaries, access and drains, and talk through what you need the new space to do.
Design and approval
Measured survey and drawings, then planning permission or a lawful development certificate, depending on the rules where you live.
Engineering and fixed price
Structural calculations and building regulations approval, then a fixed build price in writing.
Build and sign-off
Vetted teams working under S&K build it, and we arrange the completion certificate.

Questions about extensions over a garage

Can my garage take a room on top?

Sometimes, but it needs checking. Many garages are built on shallow footings with thin walls, designed only for a single storey. We dig a trial hole and inspect the walls, and the structural engineer decides whether to reuse them, strengthen them, underpin the footings or build new foundations inside the garage.

Do I need to convert the garage as well?

No. You can keep the garage for parking or storage and build only the room above, as long as the floor between them and any door into the house meet fire separation rules. Converting the garage at the same time is often good value, because the walls and foundations may be upgraded anyway.

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.

Is building over a garage cheaper than a full two-storey extension?

Usually, because the ground floor already exists. Our guide is £31,500–£46,000 including VAT at 20% for 3 m × 6 m of new first-floor space (18 m²), at West Midlands prices on our Standard spec. Costs rise if the garage foundations need underpinning or the walls need rebuilding, which we check before the price is fixed.

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.

Related services

Garage conversions with a room above

A garage conversion with a room above is a project that turns an attached garage into living space and builds a new room on top, so you gain space on both floors in one build.

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Two-storey side extensions

A two-storey side extension is a new two-floor addition built into the space beside your house, often over a driveway or side passage.

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Structural engineering for two-storey extensions

Structural engineering for a two-storey extension involves calculating how the new floors, walls and roof carry their loads down to the ground, and designing the beams, lintels, foundations and ties into the existing house to suit.

Extensions over a garage