First-floor extensions in Calne

Calne: the key facts for this kind of project.

Postcode districts: SN11
County / area: Wiltshire, England
Price region: South West England
Guide price: £26,000–£37,500 (£1,850–£2,680 per m²)
Approval route: It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission.
Nearest towns: Chippenham (5.3 miles), Devizes (6.1 miles), Melksham (7.4 miles)
Distance to Swindon: about 12.7 miles
First visit: Free, no obligation

About a first-floor extension

A first-floor extension suits you if your house already has a single-storey extension and you need more space upstairs. You get a structural check of the existing walls and foundations, a design that ties the new floor into the house, the approvals your nation needs, building regulations approval and the build, managed by us and carried out by vetted teams working under S&K.

We cover postcode district SN11 in and around Calne, along with neighbouring Chippenham, Devizes and Melksham.

What it costs in Calne

A guide price for Calne: around £26,000–£37,500 for 4 m × 3.5 m of new first-floor space (14 m²). That works out at £1,850–£2,680 per m² of new floor space, including VAT at 20%. We'll give you a written design-stage price first, then a fixed build price once the drawings are agreed.

Spec	Per m²	4 m × 3.5 m of new first-floor space (14 m²)
Essential	£1,710–£2,460 per m²	£24,000–£34,500
Standard	£1,850–£2,680 per m²	£26,000–£37,500
Premium	£2,220–£3,210 per m²	£31,000–£45,000

Planning and building regulations in Calne

In England, adding a first floor turns a single-storey extension into one of more than one storey. To be permitted development, the extension as a whole must go no more than 3 m beyond the rear wall of the original house and stay at least 7 m from the rear boundary, with matching materials and roof pitch. Over a side extension it always needs planning permission, costing £548 (or £575 for applications made from 8 December 2026).

Approval in England: Householder planning application: £548 (or £575 for applications made from 8 December 2026). Lawful development certificate: £274 (about £288 for applications from 8 December 2026). Councils should decide householder applications within 8 weeks of validation.

Building regulations: Building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end.

Design points for Calne homes

Replacing the flat roof

The existing roof usually comes off and is replaced by a new first-floor structure. The room below is exposed for a short time, so we plan temporary weatherproofing and sequence the work to keep the kitchen or living room usable for as long as possible.

Matching the roofline

A first-floor extension often changes how the back or side of the house looks more than the original single storey did. Matching the main roof pitch and materials, and keeping the ridge below the main ridge, usually gives the best result and is expected for permitted development in England.

How we'd run your project

Start at your house
We come to your home in Calne, measure up, check the ground floor walls and roof structure, and note anything near the boundaries.
Design and approvals
We draw the extension and check it against the rules for England, then apply for planning permission or a certificate of lawfulness, whichever fits.
Engineer it
Foundations sized for two floors, steels for any openings, and building control approval, all before anyone starts on site.
Build
Foundations, walls, floor, roof, windows, then first and second fix. We break through into the house as late as we can.

Questions about first-floor extensions in Calne

Do I need planning permission for a first-floor extension in Calne?

Calne is in England, so England planning rules apply. It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.

Who handles building regulations for a project in Calne?

We handle it as part of the project. What's needed in England: building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end. We prepare the drawings and the engineer's calculations, book the inspections and pass you the completion paperwork at the end.

How much does a first-floor extension cost in Calne?

Our guide for South West England, which covers Calne, is £1,850–£2,680 per m² including VAT. A typical project with 4 m × 3.5 m of new first-floor space (14 m²) comes to about £26,000–£37,500. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

What happens to the room below while the first floor is built?

The old roof is removed, so the room below is exposed for a short period. We fit temporary weather protection, plan the work so the roof comes off only when the new structure is ready, and agree with you which rooms will be out of use and for roughly how long.

Will the first-floor extension match my house?

It should, and in England matching materials and roof pitch is a condition of permitted development. We match brick, tile, mortar colour and window style where we can, and tell you at the design stage if an exact brick match is not available, so you can choose between the closest match and render or cladding.

Nearby

Close to Calne? We work across the area, including:

Other extensions in Calne

All two-storey extension services in Calne · First-floor extensions across Wiltshire

Want a figure first? Try our guide price tool, then book a free visit to firm it up.