Mountain Ash, South Wales Valleys
Semi-detached rear extension in Mountain Ash
We plan and build rear extensions for semi-detached houses for homeowners in Mountain Ash. Single or two-storey extensions for semi-detached houses, with side access and one party wall. 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. In Mountain Ash we measure the attached neighbour's extension at the survey, because it often sets the sensible depth for yours.
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 semi-detached rear extension cost in Mountain Ash?
For Mountain Ash we work from the Wales rate: £1,770–£2,880 per square metre of new floor, including VAT, standard specification. 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 |
We put a fixed price in writing once the design is agreed, and explain any provisional sums such as foundations.
Do you need planning permission for a semi-detached rear extension in Mountain Ash?
Planning for a semi-detached rear extension in Mountain Ash follows the Welsh householder rules.
The Welsh Government's householder rules let many homes add a single-storey rear extension up to 4 metres deep and 4 metres high without a planning application. Deeper projects go through a householder application, because Wales has no prior approval route.
In Wales a rear extension of more than one storey can be permitted development if the ground floor projects no more than 4 metres and the upper floor no more than 3 metres, with at least 10.5 metres to the rear boundary. It is not permitted development in conservation areas, National Parks or National Landscapes, so many double-storey schemes need a householder application.
Conservation areas, National Parks and National Landscapes restrict permitted development in Wales, and listed buildings need listed building consent. We check your house's planning history and any conservation area before drawing, so the route is clear before you spend on plans.
What are homes in Mountain Ash like to extend?
Stone terraces along the valley floors and post-war semis higher up are typical of Mountain Ash. Sloping sites are common, so floor levels and retaining walls are designed at the start.
How a semi-detached rear extension in Mountain Ash comes together
Look round and measure
A free visit to see the back of the house, measure it, check the drains and boundaries and hear what you need.
Drawings and budget
Floor plans and elevations for the options, each with a guide price.
Paperwork handled
Planning or permitted development, Building Regulations approval, structural design and party wall notices are all handled by us.
Fixed price and build
A written price for the agreed design, a start date and a named contact through the build, ending with the building control completion certificate.
Semi-detached rear extensions near Mountain Ash
From Mountain Ash, the nearest places we also cover are Treharris (3.4 miles) and Rhondda (3.4 miles).
- Semi-detached rear extension in Treharris
- Semi-detached rear extension in Rhondda
- Semi-detached rear extension in Aberdare
- Semi-detached rear extension in Merthyr Tydfil
- Semi-detached rear extension in Nelson
Other work in Mountain Ash:
FAQ
Semi-detached rear extension questions in Mountain Ash
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.
How much does a semi-detached rear extension cost in Mountain Ash?
As a guide, £1,770–£2,880 per square metre including VAT for a standard specification. For example, 3 m wide × 4 m deep (12 m²): about £21,000–£34,500 at that rate. Your written price follows the survey.
What if my neighbour has already extended?
That can make a matching depth easier to justify. We measure theirs at the survey.
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.
Can I get a price without a visit?
Our online guide-price tool gives a range in a couple of minutes. A written price needs a survey.
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.