Extensions over a garage in Cardiff

The basics for Cardiff at a glance.

Postcode districts: CF10, CF11 and CF24
County / area: Cardiff and the Vale of Glamorgan, Wales
Price region: Wales
Guide price: £29,000–£42,000 (£1,610–£2,350 per m²)
Approval route: Can be permitted development in Wales if it is 10.5 m from the side boundary, set back 1 m from the front and doesn't widen the house by more than half; otherwise planning permission.
Nearest towns: Llandaff (1.9 miles), Whitchurch (Cardiff and the Vale of Glamorgan) (2.8 miles), Penarth (2.9 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.

We cover postcode districts CF10, CF11 and CF24 in and around Cardiff, along with neighbouring Llandaff, Whitchurch (Cardiff and the Vale of Glamorgan) and Penarth.

What it costs in Cardiff

Our guide for Wales is £1,610–£2,350 per m² including VAT. On a project with 3 m × 6 m of new first-floor space (18 m²), that puts an extension over a garage in Cardiff at roughly £29,000–£42,000. Steelwork for wide openings is the item most likely to move the figure; we'll know once the engineer has designed it.

Spec	Per m²	3 m × 6 m of new first-floor space (18 m²)
Essential	£1,480–£2,160 per m²	£26,500–£39,000
Standard	£1,610–£2,350 per m²	£29,000–£42,000
Premium	£1,930–£2,820 per m²	£35,000–£50,500

Planning and building regulations in Cardiff

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).

Design points for Cardiff homes

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.

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.

How we'd run your project

Free site visit
We visit your home in Cardiff, look at the structure, access and boundaries, and talk through what you want the new rooms to do.
Get it approved
Once you're happy with the design we submit it to the council for Cardiff and deal with any questions from the planning officer.
Detail and price
Construction drawings, engineer's calculations and building control sign-off, then a written fixed price for the build.
Build it
The new structure goes up first, then we open into the house, finish inside and get the completion certificate.

Questions about extensions over a garage in Cardiff

How much does an extension over a garage cost in Cardiff?

Our guide for Wales, which covers Cardiff, is £1,610–£2,350 per m² including VAT. A typical project with 3 m × 6 m of new first-floor space (18 m²) comes to about £29,000–£42,000. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

Do I need planning permission for an extension over a garage in Cardiff?

Cardiff is in Wales, so Wales planning rules apply. Can be permitted development in Wales if it is 10.5 m from the side boundary, set back 1 m from the front and doesn't widen the house by more than half; otherwise planning permission. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.

How long does an extension over a garage take?

Allow 4 to 8 weeks for survey and design, then the approval period (councils normally decide householder applications within 8 weeks), 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.

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.

Nearby

The same service in neighbouring towns:

Other extensions in Cardiff

All two-storey extension services in Cardiff · Extensions over a garage across Cardiff and the Vale of Glamorgan

The quickest next step is a visit. We'll look at your house in Cardiff and give you an honest view of the options.