Mountain Ash, South Wales Valleys
Single-storey rear extension in Mountain Ash
We plan and build single-storey rear extensions for homeowners in Mountain Ash. Ground-floor space across the back of the house, usually for a kitchen, dining or family room. Start with a free site visit, then a written price once the design is agreed.
Mountain Ash and its postcode districts CF43 and CF45 are part of our South Wales Valleys coverage. A depth of 3 to 4 metres keeps many single-storey rear extensions in Mountain Ash within permitted development, subject to the house's planning history.
Book a free site visit
Tell us about the house and we'll call to arrange a free, no-obligation visit.
How much does a single-storey rear extension cost in Mountain Ash?
Guide prices for a single-storey rear extension in Mountain Ash start from our Wales rate of £1,770–£2,880 per square metre, including VAT. Prices in Wales sit below our West Midlands baseline; sloping sites are the main variable.
| Size | Guide price inc VAT |
|---|---|
| 3 m wide × 4 m deep (12 m²) | £21,000–£34,500 |
| 4 m wide × 5 m deep (20 m²) | £35,500–£57,500 |
| 4 m wide × 6 m deep (24 m²) | £42,500–£69,000 |
Your written price follows a measured survey and an agreed design, so it reflects your house, not an average.
Do you need planning permission for a single-storey rear extension in Mountain Ash?
The planning route for a single-storey rear extension in Mountain Ash is set by Wales's householder rules and your council.
Welsh permitted development allows a single-storey rear extension of up to 4 metres in depth and 4 metres in height, subject to boundary and garden-coverage limits. There is no larger-extension prior approval scheme in Wales.
Conservation areas, National Parks and National Landscapes restrict permitted development in Wales, and listed buildings need listed building consent. Before any drawing we look up the property's history with the council, because earlier extensions and removed rights change the answer.
What are homes in Mountain Ash like to extend?
Mountain Ash is largely terraced streets on sloping ground, where back gardens step up or down from the house. Excavation, retaining walls and drainage are priced at the survey.
How a single-storey rear extension in Mountain Ash comes together
Survey visit
We visit free of charge, measure up, check access, drainage and neighbours' extensions, and note what you want the room to do.
Options and costs
We draw layout options and price each one, so the budget shapes the design rather than surprising you later.
Approvals
Permitted development check or householder planning application, then Building Regulations drawings to the Welsh Approved Documents and structural calculations, plus party wall notices where they apply.
Written price, then build
Once the design and approvals are in place, you get a fixed written price and programme, and we build through to sign-off.
Single-storey rear extensions near Mountain Ash
Neighbouring places we cover include Treharris (3.4 miles) and Rhondda (3.4 miles).
- Single-storey rear extension in Treharris
- Single-storey rear extension in Rhondda
- Single-storey rear extension in Aberdare
- Single-storey rear extension in Merthyr Tydfil
- Single-storey rear extension in Nelson
Other work in Mountain Ash:
FAQ
Single-storey rear extension questions in Mountain Ash
Do I need a party wall agreement?
In Wales, usually yes if the extension is on or near a shared boundary or close to a neighbour's foundations. We serve the notices.
Can I live at home while the extension is built?
Usually yes. Most of the work is outside until the back wall is opened near the end, and that stage is screened off.
Do I need a structural engineer?
Yes for the beam over the new opening and usually for the foundations. Their calculations go to building control with the drawings.
Do you handle building control in Mountain Ash?
Yes. We apply to the council or a registered approver under the Welsh regulations and hand over the completion certificate.
Will I need a structural engineer?
Yes for the beam over the new opening and usually the foundations; we arrange them and their calculations go to building control.
Do I need planning permission for a rear extension in Mountain Ash?
Often not for a single-storey rear extension of up to 4 metres under Welsh permitted development. Wales has no prior approval route for deeper extensions.