Two-storey extensions for semi-detached houses in Dunoon
A two-storey extension for a semi-detached house is one of the most space-efficient ways to add bedrooms and living space to a house in Dunoon, because the new floors share one set of foundations and one roof.
We take on projects in Dunoon by arrangement. Site visits here aren't free as standard, and we'll agree travel costs with you in writing first.
Before you start in Dunoon, here's what applies.
- Postcode districts
- PA22 and PA23
- County / area
- Argyll and Bute, Scotland
- Price region
- Scotland
- Guide price
- £52,500–£71,000 (£1,880–£2,540 per m²)
- Approval route
- Planning permission is usually needed: Class 1B permitted development only applies if every part of the extension is at least 10 m from all boundaries. A building warrant is needed before work starts.
- Nearest towns
- Gourock (4.3 miles), Greenock (6.4 miles), Helensburgh (8.7 miles)
- Distance to Helensburgh
- about 8.7 miles
- First visit
- By arrangement
About a two-storey extension for a semi-detached house
A two-storey extension for a semi-detached house is a two-floor addition to the rear, the open side, or both, designed around the attached neighbour on one side. The rear is often the simplest option and can sometimes be permitted development, while a side extension uses the gap on the detached side. Both need care with the shared party wall and the neighbour's light.
We cover Dunoon (PA22 and PA23) and the places around it, including Gourock (4.3 miles), Greenock (6.4 miles) and Helensburgh.
What it costs in Dunoon
For budgeting in Dunoon, allow around £52,500–£71,000 for a two-storey extension for a semi-detached house with a 4 m × 3.5 m footprint on two floors (28 m² of new floor space). That's based on £1,880–£2,540 per m² including VAT for Scotland. Professional fees for drawings and the structural engineer are listed separately on our prices page.
| Spec | Per m² | A 4 m × 3.5 m footprint on two floors (28 m² of new floor space) |
|---|---|---|
| Essential | £1,730–£2,330 per m² | £48,500–£65,500 |
| Standard | £1,880–£2,540 per m² | £52,500–£71,000 |
| Premium | £2,260–£3,050 per m² | £63,000–£85,500 |
Planning and building standards in Dunoon
In Scotland, Class 1B permitted development needs a two-storey extension to be at least 10 m from every boundary, which a semi-detached house cannot meet on the attached side. In practice a two-storey extension to a semi needs a householder application, which costs £371 and is decided within two months, followed by a building warrant.
Approval in Scotland: Householder planning application: £371. Councils have two months to decide a local planning application.
Building standards: A building warrant from the council's building standards service before work starts, and a completion certificate at the end. Scotland uses its own Technical Handbooks.
Design points for Dunoon homes
Keeping the pair balanced
Semis are designed as matching pairs, and a side extension changes that balance. Setting the side extension back from the front wall and keeping its ridge lower helps the pair still read as a pair, which councils' design guides commonly ask for.
The attached neighbour's light
A two-storey rear extension next to the party wall can take light from the neighbour's rear windows. Councils often use a 45-degree test, so the first floor may need to be shorter than the ground floor or set in from the shared boundary.
How we'd run your project
Visit by arrangement
We agree a visit to your home in Dunoon and any travel costs with you in writing first, then look at the structure, access and boundaries.
Design and approvals
We draw the extension and check it against the rules for Scotland, then apply for planning permission or a certificate of lawfulness, whichever fits.
Price it properly
Once the engineer's calculations are in, we fix the build price in writing, with a clear list of what's included.
On site
One project lead runs the job, keeps you updated and arranges inspections at each stage until completion.
Questions about two-storey extensions for semi-detached houses in Dunoon
How long does a two-storey extension for a semi-detached house take?
Allow 4 to 8 weeks for survey and design, then the approval period (councils have two months to decide a local planning application), 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.
Do I need planning permission for a two-storey extension for a semi-detached house in Dunoon?
Dunoon is in Scotland. Planning permission is usually needed: Class 1B permitted development only applies if every part of the extension is at least 10 m from all boundaries. A building warrant is needed before work starts.
How much does a two-storey extension for a semi-detached house cost in Dunoon?
Our guide for Scotland, which covers Dunoon, is £1,880–£2,540 per m² including VAT. A typical project with a 4 m × 3.5 m footprint on two floors (28 m² of new floor space) comes to about £52,500–£71,000. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.
What if my neighbour has already extended?
That often helps. An existing extension next door can reduce the effect of yours on their light, and may show what the council accepts on your street. It can also mean building alongside their wall, so we check its position, foundations and any windows facing your plot at the survey.
Does a two-storey extension add value to a semi-detached house?
It usually adds value, but the gain is never certain. Nationwide's 2025 research found that 10% more floor area was linked to about 5% higher value, and that adding a double bedroom and bathroom to a three-bed, one-bathroom house could add up to 24%. Every street has a ceiling price, so check local sales first.
Nearby
Other towns near Dunoon:
Other extensions in Dunoon
- Rear
- Side
- Wraparound
- Part two-storey
- Over a garage
- First floor
- Detached
- Kitchen and bedrooms
- Bedroom and en-suite
All two-storey extension services in Dunoon · Two-storey extensions for semi-detached houses across Argyll and Bute
Send us your postcode and a few details. We'll get back to you to arrange a visit and talk through your options.