Two-storey side extensions in Northampton

Before you start in Northampton, here's what applies.

Postcode districts: NN1, NN2, NN3, NN4, NN5, NN6 and nearby districts
County / area: Northamptonshire, England
Price region: East Midlands
Guide price: £84,500–£113,000 (£2,010–£2,700 per m²)
Approval route: Planning permission is needed: in England, permitted development only allows single-storey extensions to the side.
Nearest towns: Wellingborough (8.8 miles), Daventry (11.7 miles), Rushden (12.2 miles)
First visit: Free, no obligation

About a two-storey side extension

A two-storey side extension suits a detached or semi-detached house with a side garden, driveway or garage wide enough to build on. You get a design that sits comfortably on the street, a planning application or permitted development check depending on your nation, structural design, building regulations approval and the build itself. We manage the whole process, and the work is carried out by vetted teams working under S&K.

We cover postcode districts NN1, NN2, NN3, NN4, NN5, NN6 and nearby districts in and around Northampton, along with neighbouring Wellingborough, Daventry and Rushden.

What it costs in Northampton

Most of the cost of a two-storey side extension is set by its size and specification. For Northampton and the rest of the East Midlands, our guide is £2,010–£2,700 per m² including VAT, so about £84,500–£113,000 for a 3 m × 7 m footprint on two floors (42 m² of new floor space). Keep a contingency of around 10% for things nobody can see until the ground is opened up.

Spec	Per m²	A 3 m × 7 m footprint on two floors (42 m² of new floor space)
Essential	£1,850–£2,480 per m²	£77,500–£104,000
Standard	£2,010–£2,700 per m²	£84,500–£113,000
Premium	£2,410–£3,230 per m²	£101,500–£136,000

Planning and building regulations in Northampton

In England, a two-storey side extension always needs householder planning permission, because permitted development only allows single-storey extensions beyond a side wall. The fee is £548 (or £575 for applications made from 8 December 2026), and councils should decide within 8 weeks of validation. Expect them to look at set-back, roof height, gaps to the boundary and the effect on neighbours.

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 Northampton homes

Set-down and set-back

Councils usually want a two-storey side extension to look subordinate to the house. Setting the front wall back from the main front and dropping the ridge slightly below the main roof helps it read as an addition, and is often expected in local design guidance.

Matching the ridge and roof

A hipped house usually needs a hipped extension roof, and a gabled house a gable. Matching the pitch, tiles, ridge detail and brick bond is what makes a side extension look original rather than added, and councils look closely at it on a front-facing addition.

How we'd run your project

Look at the house
We start in Northampton with a free visit: measurements, photos, a look at the loft and drains, and a frank chat about budget.
Get it approved
Once you're happy with the design we submit it to the council for Northampton and deal with any questions from the planning officer.
Price it properly
Once the engineer's calculations are in, we fix the build price in writing, with a clear list of what's included.
Build it
The new structure goes up first, then we open into the house, finish inside and get the completion certificate.

Questions about two-storey side extensions in Northampton

Do I need planning permission for a two-storey side extension in Northampton?

Northampton is in England, so England planning rules apply. Planning permission is needed: in England, permitted development only allows single-storey extensions to the side. 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 Northampton?

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 Northampton?

We cover Northampton (NN1, NN2, NN3, NN4, NN5, NN6 and nearby districts) and nearby places including Wellingborough, Daventry and Rushden, plus the rest of Northamptonshire. The first site visit is free.

How much does a two-storey side extension cost in Northampton?

Our guide for the East Midlands, which covers Northampton, is £2,010–£2,700 per m² including VAT. A typical project with a 3 m × 7 m footprint on two floors (42 m² of new floor space) comes to about £84,500–£113,000. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

Can I build a two-storey side extension over my driveway?

Yes, if the drive is wide enough for a useful room and the council accepts the design. You may lose off-road parking, which some councils weigh up, and the foundations need to suit the ground below. We check parking, drains and meter positions at the free site visit before any drawings are prepared.

Nearby

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

Other extensions in Northampton

All two-storey extension services in Northampton · Two-storey side extensions across Northamptonshire

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