Northamptonshire
Rear extensions for detached houses in Northamptonshire
Wider, deeper rear extensions with room for vaulted roofs and big glazing. Rear extensions in Northamptonshire: we cover 8 towns including Northampton, Corby and Kettering, with design, approvals and the build under one contract.
Detached houses in Northamptonshire often have room for a deeper rear extension under England's prior approval route or a full-width design. Northamptonshire has plenty of inter-war semis and bungalows, and single-storey rear extensions suit both.
How much does a detached house rear extension cost in Northamptonshire?
A detached house rear extension in Northamptonshire is priced at £1,890–£3,100 per square metre including VAT as a guide, before kitchen fit-out and fees. East Midlands prices sit a little below our West Midlands baseline.
| Size | Guide price inc VAT |
|---|---|
| 4 m wide × 6 m deep (24 m²) | £45,500–£74,500 |
| 5 m wide × 8 m deep (40 m²) | £75,500–£124,000 |
These are guide ranges; the written quote after the survey is the figure that counts.
Do you need planning permission in Northamptonshire?
English permitted development (Class A) allows a single-storey rear extension of 3 metres on a terraced or semi-detached house and 4 metres on a detached one, measured from the original house, with a maximum height of 4 metres and eaves of no more than 3 metres within 2 metres of a boundary.
If 3 or 4 metres is not enough, England's prior approval route allows 6 metres on a terraced or semi-detached house and 8 metres on a detached house for a single-storey rear extension. Neighbours are consulted, the council decides within 42 days, and the fee is £249, rising to £310 from 8 December 2026.
England's rules allow a rear extension of more than one storey without an application only when it is no deeper than 3 metres and at least 7 metres from the boundary opposite the rear wall, and never on designated land. Most two-storey schemes need householder planning permission.
Conservation areas, National Parks, National Landscapes and the Broads restrict permitted development, and listed buildings always need listed building consent.
Where in Northamptonshire do we work?
FAQ
Questions people ask
How deep can I extend a detached house?
4 metres under permitted development in England, or 8 metres with prior approval, outside designated land.
Can I have a vaulted ceiling?
Yes, with a pitched roof and exposed or boxed rafters, subject to the height limits.
Is an oak frame worth it?
It is a premium finish with a long life; it costs more than blockwork with a plain roof.
Do you cover all of Northamptonshire?
We cover 8 towns and districts in Northamptonshire, including Northampton, Corby and Kettering.
Who builds the extension?
Vetted building teams working under contract to us; your contract is with S&K Property Investments and Improvement Ltd.