Side extensions in Cardiff
Our design and build teams take on side extensions in Cardiff, from the first measured survey through planning and building control to the finished room.
- Guide price in CardiffFrom £20,000 inc VAT
- PlanningSingle storey can be permitted development
- Build time10–18 weeks on site
- Postcode districtsCF5, CF10, CF11, CF14, CF23
How much does a side extension cost in Cardiff?
Prices below are for Cardiff, using the Wales factor of ×0.93. They are guide ranges including VAT for the build only, not a quote.
Typical rates in Cardiff: £1,630 to £3,160 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| 2.5 m × 5 m 12 m² | £20,000 – £25,000 | £22,500 – £30,000 | £29,000 – £38,000 |
| 3 m × 6 m 18 m² | £29,000 – £35,500 | £34,000 – £44,500 | £43,500 – £57,000 |
| 3 m × 8 m 24 m² | £39,000 – £47,000 | £45,500 – £59,500 | £58,000 – £76,000 |
Want a range for your exact size? The guide-price tool takes about a minute.
Planning rules that apply in Cardiff
In Wales a single-storey side extension can be permitted development if it is no more than 4 m high and no wider than half the width of the original house, and it must not come closer to a highway than the existing side wall. Larger side extensions need planning permission.
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.
The Party Wall etc. Act 1996 applies in Wales as in England: notice must be served before work to a shared wall, building on the boundary, or excavating close to a neighbour's foundations.
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).
Who a side extension suits
- Houses where the rear garden is small
- Homes needing a utility, study or ground-floor bedroom
- Detached and semi-detached houses with side land
Councils often prefer side extensions to sit slightly back from the front of the house with a lower roof, so the original building still reads clearly. We design to those principles from the start to avoid redesigns.
Local to Cardiff
Across CF5, CF10, CF11, CF14, CF23, CF24, we can visit, measure and advise. Neighbouring towns we cover include Penarth (3 miles), Barry (7 miles), Cowbridge (12 miles).
Just over the Mid Glamorgan border, Caerphilly is about 7 miles away. In Wales, terraced houses with rear offshoots are common in the towns, while detached houses and bungalows dominate in rural areas.
From first visit to completion
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
It starts with a visit to your house to measure, check access and talk through ideas and budget.
Design and approvals
Once the layout is agreed, we deal with the council: planning permission or written confirmation that none is needed, plus building control.
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
The build is managed from start to finish, inspected at each stage and signed off on completion.
Side extension questions answered
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.
Will my neighbours in Cardiff be involved?
If a planning application is needed, the council notifies neighbours. If the work is on or near a shared boundary, party wall notices may also be needed.
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.
Can I build over my driveway?
Yes, if the foundations work and you keep any parking the council requires. Drains and services under drives are common, so we check before design.
How much does a side extension cost?
Our guide range is about £1,630 to £3,160 per m² including VAT, depending on specification, so a standard 18 m² single-storey side extension lands around £34,000 to £44,500 in Cardiff.
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.