Two-storey extensions for semi-detached houses in Mayfield

Mayfield: the key facts for this kind of project.

Postcode districts: EH37
County / area: Edinburgh and the Lothians, 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: Gorebridge (1.8 miles), Dalkeith (1.9 miles), Bonnyrigg (2.6 miles)
Distance to Edinburgh: about 8.3 miles
First visit: Free, no obligation

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 Mayfield (EH37) and the places around it, including Gorebridge (1.8 miles), Dalkeith (1.9 miles) and Bonnyrigg.

What it costs in Mayfield

Most of the cost of a two-storey extension for a semi-detached house is set by its size and specification. For Mayfield and the rest of Scotland, our guide is £1,880–£2,540 per m² including VAT, so about £52,500–£71,000 for a 4 m × 3.5 m footprint on two floors (28 m² of new floor space). These are guides, not quotes. Ground conditions, steelwork and access can move the figure either way.

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 Mayfield

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 Mayfield homes

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.

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.

How we'd run your project

Start at your house
We come to your home in Mayfield, measure up, check the ground floor walls and roof structure, and note anything near the boundaries.
Drawings and permission
Our designers produce plans and elevations, then we take care of planning or permitted development checks with the council covering Mayfield.
Technical design
We prepare the building warrant drawings, structural calculations and specification so the build price can be fixed.
Build and sign-off
Vetted teams working under S&K build the extension, and we arrange the completion certificate at the end.

Questions about two-storey extensions for semi-detached houses in Mayfield

How much does a two-storey extension for a semi-detached house cost in Mayfield?

Our guide for Scotland, which covers Mayfield, 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.

Which postcodes do you cover around Mayfield?

We cover Mayfield (EH37) and nearby places including Gorebridge, Dalkeith and Bonnyrigg, plus the rest of Edinburgh and the Lothians. The first site visit is free.

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.

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.

Will a side extension make my semi look like a terrace?

It can if it fills the whole gap to the boundary at first floor and the neighbour does the same. Many councils ask for a first-floor gap to the side boundary or a set-back for this reason. We design the extension to keep the semi reading as one of a pair.

Nearby

Other towns near Mayfield:

Other extensions in Mayfield

All two-storey extension services in Mayfield · Two-storey extensions for semi-detached houses across Edinburgh and the Lothians

Ready to talk it through? Call us or send the form and we'll arrange a visit to your home in Mayfield.