South Wales Valleys
Rear extensions in Mountain Ash
Rear extensions in Mountain Ash: single-storey and two-storey extensions, side returns, wraparounds and glass-led designs, planned around terraced streets on sloping ground and the Welsh rules.
Mountain Ash is in the South Wales Valleys, with postcode districts including CF43 and CF45. The nearest places we also cover are Treharris (3.4 miles) and Rhondda (3.4 miles).
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Tell us about the house and we'll call to arrange a free, no-obligation visit.
Rear extensions we build in Mountain Ash
- Single-storey rear extensions
- Two-storey rear extensions
- Kitchen-diner rear extensions
- Side return extensions
- Wraparound extensions
- Glazed and glass-box rear extensions
- Rear extensions for terraced houses
- Rear extensions for semi-detached houses
- Rear extensions for bungalows
- Rear extension plans and planning applications
Also available across the South Wales Valleys:
- Rear extensions for detached houses
- Flat-roof rear extensions
- Pitched and lean-to roof rear extensions
- Knocking through to a rear extension
- Roof lanterns and rooflights for rear extensions
- Permitted development rear extensions
- Building Regulations for rear extensions
Rear extension prices in Mountain Ash
Prices in Wales sit below our West Midlands baseline; sloping sites are the main variable.
| Example | Guide inc VAT |
|---|---|
| Single-storey, 3 m × 4 m (12 m²) | £21,000–£34,500 |
| Single-storey, 4 m × 6 m (24 m²) | £42,500–£69,000 |
| Two-storey, 3 m × 5 m footprint (30 m²) | £50,000–£75,500 |
| Side return, about 14 m² | £30,000–£49,500 |
| Wraparound, about 25 m² | £51,000–£83,500 |
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.
Planning rules for Mountain Ash
In Wales a single-storey rear extension can often be permitted development if it projects no more than 4 metres beyond the rear wall and is no more than 4 metres high. Wales has no prior approval route for deeper extensions, so anything bigger needs a householder planning application.
In Wales a rear extension needs Building Regulations approval through the council or a registered approver, and is built to the Welsh Approved Documents, which differ from England's in places, including energy efficiency.
Nearby towns
FAQ
Questions people ask
How much is a rear extension in Mountain Ash?
A 3 m × 4 m single-storey rear extension is about £21,000–£34,500 including VAT at our Wales guide rates; the written price follows a survey.
Do I need planning permission 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.
Is the site visit in Mountain Ash free?
Yes, with no obligation.
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.