Single-storey rear extensions in Cardiff
A single-storey extension in Cardiff starts with the right design and the right approval route. We take care of both, then build it with our own project management.
- Guide price in CardiffFrom £19,500 inc VAT
- PlanningWelsh permitted development rules (rear up to 4 m)
- Build time10–16 weeks on site
- Postcode districtsCF5, CF10, CF11, CF14, CF23
Local to Cardiff
Our survey diary covers Cardiff, including CF5, CF10, CF11, CF14, CF23, CF24. Nearby, we also take on projects in Penarth (3 miles), Barry (7 miles), Cowbridge (12 miles).
Caerphilly, in Mid Glamorgan, is roughly 7 miles from Cardiff and also on our list. In Wales, terraced houses with rear offshoots are common in the towns, while detached houses and bungalows dominate in rural areas.
When a single-storey extension makes sense
- Homeowners who want open-plan living onto the garden
- Semi-detached and detached houses with a usable rear garden
- Terraced houses that want a deeper kitchen across the full width
Depth is the big decision. Every extra metre adds floor area but also takes garden and can push you out of permitted development. We draw the room at two or three depths so you can see the trade-off in space, light and cost before anything is fixed.
Single-storey extension prices in Cardiff
These guide figures apply our Wales adjustment (×0.93) to national rates. They include VAT at 20% and cover the build itself; design and council fees are listed separately.
Typical rates in Cardiff: £1,630 to £3,160 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| 3 m × 4 m 12 m² | £19,500 – £23,000 | £22,500 – £29,500 | £29,000 – £38,000 |
| 4 m × 5 m 20 m² | £32,500 – £38,500 | £38,000 – £48,500 | £48,000 – £63,500 |
| 5 m × 6 m 30 m² | £48,500 – £57,500 | £57,000 – £73,000 | £72,500 – £95,000 |
For a figure based on your own dimensions, use our guide-price tool.
Will the council need to approve it?
In Wales a single-storey rear extension can usually project up to 4 m beyond the rear wall without a planning application, if it is no more than 4 m high, keeps eaves to 3 m and overall height to 4 m within 2 m of a boundary, and covers no more than half the land around the original house. Wales has no larger home extension prior approval scheme.
In a conservation area, national park, National Landscape or World Heritage Site the permitted development limits are tighter (no side or two-storey extensions without an application). Listed homes need listed building consent, and if permitted development rights have been removed, any extension needs an application.
Building regulations approval is separate from planning. Wales has its own building regulations and approved documents; the council or a registered building control approver checks the plans, inspects the work and issues a completion certificate.
Building over or within 3 m of a public sewer needs the water company's consent before the foundations go in.
Applications are decided by the local planning authority (your county or county borough council, or the national park authority).
Our process, step by step
Site visits are free and there is no obligation. Where drawings are needed, the design stage is priced in writing before it starts.
Free site visit
First, a site visit: we look at the house, garden, access and drains and listen to what you need.
Design and approvals
Drawings are prepared and agreed with you, then submitted for the right planning route and building regulations approval.
Fixed written price
We confirm the build price in writing, based on the approved drawings and the finishes you have chosen.
Build and sign-off
We build it with one project manager, book the building control inspections and hand over the completion certificate.
Common questions in Cardiff
Do I need building regulations approval in Cardiff?
Yes. Almost every extension needs it, whatever the planning route. We prepare the drawings and book the inspections.
How long does a single-storey extension take to build in Cardiff?
On site, typically 10 to 16 weeks once approvals are in place. Before that, allow 4–12 weeks design and approvals.
Can I see a price before committing to anything?
Yes. The guide prices on this page are adjusted for Cardiff, and the guide-price tool gives a range for your own size. After the survey you get a written price before anything is agreed.
How much does a single-storey extension cost per square metre?
Our guide range is about £1,630 to £3,160 per m² including VAT, depending on specification. A standard-spec 4 m × 5 m room usually lands at £38,000 to £48,500 in Cardiff, plus design and council fees.
Can I stay in the house during the build?
Usually yes. Most of the work happens outside until the final weeks, when we open the rear wall. We plan that stage carefully and seal the opening with a temporary screen to keep dust down.
Book a free site visit in Cardiff
We will measure up, check the planning position and give you honest guide figures.
- Free, no-obligation site visit
- Planning route checked before you spend on drawings
- Written price once the design is agreed
- Building control sign-off at the end
Prefer to talk? Call 0800 088 6341 or .
Book a free site visit
Tell us a little about the project and we will arrange a time.