Mountain Ash, South Wales Valleys
Two-storey rear extension in Mountain Ash
A larger kitchen downstairs and an extra bedroom or bathroom upstairs, under one roof. If you live in Mountain Ash and want to know what a two-storey rear extension would cost and whether it needs planning, start with the online guide price or a free site visit.
Mountain Ash is covered from our South Wales Valleys round, including CF43 and CF45. In Mountain Ash, a two-storey rear extension is worth comparing with the cost of moving once stamp duty, agents' and legal fees are counted.
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 two-storey rear extension cost in Mountain Ash?
In Mountain Ash, our guide for a two-storey rear extension is £1,670–£2,510 per square metre including VAT for a standard specification. Prices in Wales sit below our West Midlands baseline; sloping sites are the main variable.
| Size | Guide price inc VAT |
|---|---|
| 3 m × 5 m footprint, two floors (30 m²) | £50,000–£75,500 |
| 4 m × 6 m footprint, two floors (48 m²) | £80,500–£120,500 |
These are guide ranges; the written quote after the survey is the figure that counts.
Do you need planning permission for a two-storey rear extension in Mountain Ash?
Whether your two-storey rear extension in Mountain Ash needs a planning application depends on its size, your house and any local restrictions.
Welsh rules allow a two-storey rear extension without an application only where the ground floor is no deeper than 4 metres, the upper floor no deeper than 3 metres and at least 10.5 metres remains to the rear boundary. Most homeowners still apply for householder planning permission.
Conservation areas, National Parks and National Landscapes restrict permitted development in Wales, and listed buildings need listed building consent. At the first visit we measure what is there now and tell you which route fits: permitted development or a householder planning application.
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 two-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.
Drawings and budget
Floor plans and elevations for the options, each with a guide price.
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.
Two-storey rear extensions near Mountain Ash
Close by, we work in Treharris, about 3.4 miles away, and Rhondda, about 3.4 miles away.
- Two-storey rear extension in Treharris
- Two-storey rear extension in Rhondda
- Two-storey rear extension in Aberdare
- Two-storey rear extension in Merthyr Tydfil
- Two-storey rear extension in Nelson
Other work in Mountain Ash:
FAQ
Two-storey rear extension questions in Mountain Ash
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.
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.
What is the 45-degree rule?
Many councils check that a two-storey extension does not cross a 45-degree line drawn from the nearest habitable window of the neighbouring house. We test it at the first drawing.
Is the site visit in Mountain Ash free?
Yes. We visit, measure up and talk through the options with no cost and no obligation.
Who will build my extension?
Vetted building teams working under contract to us. Your contract is with S&K Property Investments and Improvement Ltd for the design and the build.
How much does a two-storey rear extension cost in Mountain Ash?
As a guide, £1,670–£2,510 per square metre including VAT for a standard specification. For example, 3 m × 5 m footprint, two floors (30 m²): about £50,000–£75,500 at that rate. Your written price follows the survey.