Two-storey side extensions in Mountain Ash
We plan and build two-storey side extensions for homeowners in Mountain Ash and nearby. Every project starts with a free visit and a design stage priced in writing before any work begins.
Before you start in Mountain Ash, here's what applies.
- Postcode districts
- CF45
- County / area
- Mid Glamorgan, Wales
- Price region
- Wales
- Guide price
- £79,000–£106,500 (£1,890–£2,530 per m²)
- Approval route
- Can be permitted development in Wales if it is 10.5 m from the side boundary, set back 1 m from the front and doesn't widen the house by more than half; otherwise planning permission.
- Nearest towns
- Abercanaid (2.8 miles), Ferndale (3.3 miles), Treharris (3.4 miles)
- Distance to Rhondda
- about 3.4 miles
- First visit
- Free, no obligation
About a two-storey side extension
A two-storey side extension suits a detached or semi-detached house with a side garden, driveway or garage wide enough to build on. You get a design that sits comfortably on the street, a planning application or permitted development check depending on your nation, structural design, building regulations approval and the build itself. We manage the whole process, and the work is carried out by vetted teams working under S&K.
We cover postcode district CF45 in and around Mountain Ash, along with neighbouring Abercanaid, Ferndale and Treharris.
What it costs in Mountain Ash
For budgeting in Mountain Ash, allow around £79,000–£106,500 for a two-storey side extension with a 3 m × 7 m footprint on two floors (42 m² of new floor space). That's based on £1,890–£2,530 per m² including VAT for Wales. The fastest way to a firmer number is a free site visit, after which we price the design stage in writing.
| Spec | Per m² | A 3 m × 7 m footprint on two floors (42 m² of new floor space) |
|---|---|---|
| Essential | £1,740–£2,330 per m² | £73,000–£98,000 |
| Standard | £1,890–£2,530 per m² | £79,000–£106,500 |
| Premium | £2,260–£3,040 per m² | £95,000–£127,500 |
Planning and building regulations in Mountain Ash
In Wales, a two-storey side extension can be permitted development if it is at least 10.5 m from the boundary opposite the side wall, set back at least 1 m from the front of the house and does not increase the house's widest width by more than 50%. If it fails any test, or the house is in a protected area, a householder application costs £585.
Approval in Wales: Householder planning application: £585. Councils normally decide householder applications within 8 weeks.
Building regulations: Building regulations approval under the Welsh Approved Documents, which differ from England's in places (notably energy efficiency).
Design points for Mountain Ash homes
Matching the ridge and roof
A hipped house usually needs a hipped extension roof, and a gabled house a gable. Matching the pitch, tiles, ridge detail and brick bond is what makes a side extension look original rather than added, and councils look closely at it on a front-facing addition.
Avoiding a terracing effect
Where semi-detached houses sit close together, side extensions on neighbouring houses can join up and turn a row of pairs into a terrace. Many councils ask for a gap to the boundary at first floor to stop this, so we check local guidance before fixing the width.
How we'd run your project
Visit and first ideas
One of our team visits your house in Mountain Ash, checks the walls, roof and drains, and sketches out options with you.
Plans, then approval
Measured survey, design, then the right approval route for your house. We explain each step before we take it.
Detail and price
Construction drawings, engineer's calculations and building control sign-off, then a written fixed price for the build.
On site
One project lead runs the job, keeps you updated and arranges inspections at each stage until completion.
Questions about two-storey side extensions in Mountain Ash
Which postcodes do you cover around Mountain Ash?
We cover Mountain Ash (CF45) and nearby places including Abercanaid, Ferndale and Treharris, plus the rest of Mid Glamorgan. The first site visit is free.
How long does a two-storey side extension take?
Allow 4 to 8 weeks for survey and design, then the approval period (councils normally decide householder applications within 8 weeks), then 4 to 8 weeks of technical design, which can overlap. The build itself usually takes 14 to 20 weeks, longer for large or complex designs.
How much does a two-storey side extension cost in Mountain Ash?
Our guide for Wales, which covers Mountain Ash, is £1,890–£2,530 per m² including VAT. A typical project with a 3 m × 7 m footprint on two floors (42 m² of new floor space) comes to about £79,000–£106,500. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.
Do I need planning permission for a two-storey side extension in Mountain Ash?
Mountain Ash is in Wales, so Wales planning rules apply. Can be permitted development in Wales if it is 10.5 m from the side boundary, set back 1 m from the front and doesn't widen the house by more than half; otherwise planning permission. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.
Can I build a two-storey side extension over my driveway?
Yes, if the drive is wide enough for a useful room and the council accepts the design. You may lose off-road parking, which some councils weigh up, and the foundations need to suit the ground below. We check parking, drains and meter positions at the free site visit before any drawings are prepared.
Nearby
Close to Mountain Ash? We work across the area, including:
Other extensions in Mountain Ash
- Rear
- Wraparound
- Part two-storey
- Over a garage
- First floor
- Semi-detached
- Detached
- Kitchen and bedrooms
- Bedroom and en-suite
All two-storey extension services in Mountain Ash · Two-storey side extensions across Mid Glamorgan
Book a free site visit in Mountain Ash and we'll tell you what's possible, what approvals you need and what the design stage would cost.