Two-storey side extensions in Northamptonshire
Northamptonshire has a wide mix of house types, and most can take a well-designed two-storey side extension. Here's what's involved, the rules in England and typical costs.
Northamptonshire at a glance
- Nation
- England
- Price region
- East Midlands
- Postcode areas
- LE, NN
- Towns covered
- 9 listed below, plus surrounding villages
- Approval route
- Planning permission is needed: in England, permitted development only allows single-storey extensions to the side.
- Site visits
- Free, no obligation
What a two-storey side extension involves
A two-storey side extension is a new two-floor addition built into the space beside your house, often over a driveway or side passage. It typically adds one or two bedrooms upstairs and a utility, study or larger kitchen below, without giving up rear garden.
The main places we list in Northamptonshire are Northampton (NN1), Corby (NN17), Kettering (NN14), Wellingborough (NN8), Rushden (NN9) and Daventry (NN11). We cover the villages in between too.
Guide price in the East Midlands
Expect a two-storey side extension in Northamptonshire to land somewhere around £84,500–£113,000 for a 3 m × 7 m footprint on two floors (42 m² of new floor space). Our East Midlands guide rate is £2,010–£2,700 per m², including VAT. Kitchens, bathroom fittings and flooring are priced separately so you can compare like with like.
| Spec | Per m² | Typical project |
|---|---|---|
| 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 |
Rules in England
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.
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
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.
Access and services
Side extensions often cover the only route to the back garden, a gas meter, soil pipes or a drain run. We plan bin and bike access, move meters and pipes where needed and check drains early, because these items affect both cost and layout.
How we work in Northamptonshire
Measure and listen
A visit to Northamptonshire to understand how you live in the house now and what the extra rooms need to do, plus a first look at the structure.
Plans, then approval
Measured survey, design, then the right approval route for your house. We explain each step before we take it.
Structure and building control
A structural engineer sizes the foundations and steels, and we get building regulations approval before work starts.
Finish and certify
Second fix, plastering and making good, then building control's final inspection and the completion paperwork.
Towns we cover in Northamptonshire
Two-storey side extensions in Northamptonshire: questions
How much does a two-storey side extension cost in Northamptonshire?
In 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). Essential and Premium specs move that by roughly 8% down or 20% up.
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.
Will I need planning permission in Northamptonshire?
Northamptonshire is in England. Planning permission is needed: in England, permitted development only allows single-storey extensions to the side.
Neighbouring areas
- Two-storey side extensions in Rutland
- Two-storey side extensions in Leicestershire
- Two-storey side extensions in Bedfordshire
- Two-storey side extensions in Warwickshire
All extension services in Northamptonshire · About two-storey side extensions
Ready to see what a second storey could do for your home?
Book a free site visit. We'll look at your house, talk through options and explain the approvals you'd need, then price the design stage in writing.