First-floor extensions in Derby

Useful details for planning a first-floor extension in Derby.

Postcode districts: DE1, DE3 and DE22
County / area: Derbyshire, England
Price region: East Midlands
Guide price: £24,500–£35,500 (£1,760–£2,550 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: Chaddesden (1.8 miles), Oakwood (Derbyshire) (2.4 miles), Sinfin (2.9 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.

Around Derby we also work in Chaddesden, Oakwood (Derbyshire) and Sinfin, and across the rest of Derbyshire. Postcode districts in and near Derby: DE1, DE3 and DE22.

What it costs in Derby

Using our East Midlands rates, a first-floor extension with 4 m × 3.5 m of new first-floor space (14 m²) comes to about £24,500–£35,500, including VAT. Bigger or more glazed designs cost more per m². These are guides, not quotes. Ground conditions, steelwork and access can move the figure either way.

Spec	Per m²	4 m × 3.5 m of new first-floor space (14 m²)
Essential	£1,620–£2,340 per m²	£22,500–£33,000
Standard	£1,760–£2,550 per m²	£24,500–£35,500
Premium	£2,120–£3,060 per m²	£29,500–£43,000

Planning and building regulations in Derby

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 Derby 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

Look at the house
We start in Derby with a free visit: measurements, photos, a look at the loft and drains, and a frank chat about budget.
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.
Build and sign-off
Vetted teams working under S&K build the extension, and we arrange the building control completion certificate at the end.

Questions about first-floor extensions in Derby

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

Derby 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.

Which postcodes do you cover around Derby?

We cover Derby (DE1, DE3 and DE22) and nearby places including Chaddesden, Oakwood (Derbyshire) and Sinfin, plus the rest of Derbyshire. The first site visit is free.

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

Our guide for the East Midlands, which covers Derby, is £1,760–£2,550 per m² including VAT. A typical project with 4 m × 3.5 m of new first-floor space (14 m²) comes to about £24,500–£35,500. 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.

Can I build on top of my existing single-storey extension?

Often yes, but only after the structure has been checked. Foundations, walls and lintels built for one storey may not carry two. We dig trial holes, look for the original building control approval and ask the structural engineer to confirm what can stay, what needs strengthening and what must be rebuilt.

Nearby

The same service in neighbouring towns:

Other extensions in Derby

All two-storey extension services in Derby · First-floor extensions across Derbyshire

Send us your postcode and a few details. We'll get back to you to arrange a visit and talk through your options.