Extensions over a garage in Northampton

What we'd confirm first for a project in Northampton.

Postcode districts: NN1, NN2, NN3, NN4, NN5, NN6 and nearby districts
County / area: Northamptonshire, England
Price region: East Midlands
Guide price: £31,000–£45,000 (£1,720–£2,500 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 an extension over a garage

An extension over a garage is a new first-floor room built on top of an existing attached garage, usually a bedroom, en-suite or study. It uses a footprint you already have, so it adds floor space without taking any garden. The garage walls and foundations often need strengthening or replacing to carry the new floor.

Around Northampton we also work in Wellingborough, Daventry and Rushden, and across the rest of Northamptonshire. Postcode districts in and near Northampton: NN1, NN2, NN3, NN4, NN5, NN6 and nearby districts.

What it costs in Northampton

Using our East Midlands rates, an extension over a garage with 3 m × 6 m of new first-floor space (18 m²) comes to about £31,000–£45,000, including VAT. Bigger or more glazed designs cost more per m². Keep a contingency of around 10% for things nobody can see until the ground is opened up.

Spec	Per m²	3 m × 6 m of new first-floor space (18 m²)
Essential	£1,580–£2,300 per m²	£28,500–£41,500
Standard	£1,720–£2,500 per m²	£31,000–£45,000
Premium	£2,060–£3,000 per m²	£37,000–£54,000

Planning and building regulations in Northampton

In England, most garages sit beside the house, so building over one makes a two-storey extension beyond a side wall, which always needs planning permission. If the garage is at the rear, the 3 m and 7 m rules for two-storey rear extensions apply, measured from the original house. A householder application costs £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 Northampton homes

Floor levels and headroom

Garage floors are often lower than the house, and the new first floor may not line up with the existing landing. We set the floor level to avoid awkward steps upstairs, while keeping enough headroom in the garage below for a car or storage.

Checking the garage foundations

Garages are often built on shallow strip footings sized for a single-storey wall and a light roof. A trial hole shows their depth and condition, and the engineer decides whether they can carry two storeys or need underpinning or new foundations inside the garage.

How we'd run your project

Start at your house
We come to your home in Northampton, measure up, check the ground floor walls and roof structure, and note anything near the boundaries.
Drawings and permission
Our designers produce plans and elevations, then we take care of planning or permitted development checks with the council covering Northampton.
Engineer it
Foundations sized for two floors, steels for any openings, and building control approval, all before anyone starts on site.
On site
One project lead runs the job, keeps you updated and arranges inspections at each stage until completion.

Questions about extensions over a garage in Northampton

How much does an extension over a garage cost in Northampton?

Our guide for the East Midlands, which covers Northampton, is £1,720–£2,500 per m² including VAT. A typical project with 3 m × 6 m of new first-floor space (18 m²) comes to about £31,000–£45,000. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

How long does an extension over a garage take?

Allow 4 to 8 weeks for survey and design, then the approval period (councils should decide householder applications within 8 weeks of validation), then 4 to 8 weeks of technical design, which can overlap. The build itself usually takes 14 to 20 weeks, longer for large or complex designs.

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.

Can I add an en-suite above the garage?

Yes, and it is a common choice for a main bedroom. The en-suite needs an extract fan under Part F, a route for the soil pipe down to the drains and enough fall for the waste, which can be harder over a garage. We plan the pipe route through the garage or an outside wall early.

How do I get into a room over the garage?

Usually through a new opening off the existing landing or a bedroom, so the stairs stay where they are. If the floor levels do not match, a step or two may be needed inside the new room. Where a landing opening is not practical, a new stair from a converted garage is an option.

Nearby

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

Other extensions in Northampton

All two-storey extension services in Northampton · Extensions over a garage across Northamptonshire

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