First-floor extensions in Daventry

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

Postcode districts: NN11
County / area: Northamptonshire, 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: Rugby (9 miles), Northampton (11.7 miles), Lutterworth (13.9 miles)
Distance to Northampton: about 11.7 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.

Around Daventry we also work in Rugby, Northampton and Lutterworth, and across the rest of Northamptonshire. Postcode district in and near Daventry: NN11.

What it costs in Daventry

For budgeting in Daventry, 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. Design fees, structural calculations and approval fees are separate and listed on our prices page.

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 Daventry

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 Daventry homes

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.

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.

How we'd run your project

Free site visit
We visit your home in Daventry, look at the structure, access and boundaries, and talk through what you want the new rooms to do.
Drawings and permission
Our designers produce plans and elevations, then we take care of planning or permitted development checks with the council covering Daventry.
Engineer it
Foundations sized for two floors, steels for any openings, and building control approval, all before anyone starts on site.
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 Daventry

Who handles building regulations for a project in Daventry?

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.

Which postcodes do you cover around Daventry?

We cover Daventry (NN11) and nearby places including Rugby, Northampton and Lutterworth, plus the rest of Northamptonshire. The first site visit is free.

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

Daventry 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.

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.

Nearby

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

Other extensions in Daventry

All two-storey extension services in Daventry · First-floor extensions across Northamptonshire

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