First-floor extensions in Derbyshire

Derbyshire at a glance

Nation: England
Price region: East Midlands
Postcode areas: DE, NG, S, SK
Towns covered: 22 listed below, plus surrounding villages
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.
Site visits: Free, no obligation

What a first-floor extension involves

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.

Across Derbyshire we cover Derby (DE1), Chesterfield (S40), Long Eaton (DE72), Ilkeston (DE7), Swadlincote (DE11) and Staveley (S43), plus the smaller places around them.

Guide price in the East Midlands

For budgeting in Derbyshire, allow around £24,500–£35,500 for a first-floor extension with 4 m × 3.5 m of new first-floor space (14 m²). That's based on £1,760–£2,550 per m² including VAT for the East Midlands. Steelwork for wide openings is the item most likely to move the figure; we'll know once the engineer has designed it.

Spec	Per m²	Typical project
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

Rules in England

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.

The Party Wall etc. Act 1996 applies, so notices may be needed for work on or near a shared wall or boundary.

Getting the design right

Escape and fire safety

A new first-floor bedroom needs an escape window with a clear opening of at least 0.33 m², at least 450 mm wide and 450 mm high, with the bottom no more than 1,100 mm above the floor, unless there is a protected route to the stairs.

Can the existing structure take it?

Many single-storey extensions were built with foundations, walls and lintels sized for one storey. We find out what is there with trial holes and, where available, the original building control drawings. The engineer then decides whether to reuse, strengthen or rebuild parts of the structure.

How we work in Derbyshire

Measure and listen
A visit to Derbyshire to understand how you live in the house now and what the extra rooms need to do, plus a first look at the structure.
Choose the approval route
Some designs fit permitted development, most need a householder application. We decide which applies in England before drawing in detail.
Engineer it
Foundations sized for two floors, steels for any openings, and building control approval, all before anyone starts on site.
Finish and certify
Second fix, plastering and making good, then building control's final inspection and the completion paperwork.

Towns we cover in Derbyshire

First-floor extensions in Derbyshire: questions

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

In the East Midlands our guide is £1,760–£2,550 per m² including VAT, so about £24,500–£35,500 for 4 m × 3.5 m of new first-floor space (14 m²). Essential and Premium specs move that by roughly 8% down or 20% up.

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.

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.

Will I need planning permission in Derbyshire?

Derbyshire is in England. 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.

Neighbouring areas

All extension services in Derbyshire · About first-floor extensions