Barnet, Greater London
Semi-detached rear extension in Barnet
Semi-detached rear extension in Barnet: single or two-storey extensions for semi-detached houses, with side access and one party wall. We measure the house, show you what the rules allow, price it in writing and build it.
Barnet sits in Greater London, with postcode districts including EN4, EN5, N3 and N12. In Barnet we measure the attached neighbour's extension at the survey, because it often sets the sensible depth for yours.
Book a free site visit
Tell us about the house and we'll call to arrange a free, no-obligation visit.
How much does a semi-detached rear extension cost in Barnet?
A semi-detached rear extension in Barnet is priced at £2,470–£4,030 per square metre including VAT as a guide, before kitchen fit-out and fees. London prices sit at the top of our range because of labour rates, access through the house, parking suspensions and skip licences.
| Size | Guide price inc VAT |
|---|---|
| 3 m wide × 4 m deep (12 m²) | £29,500–£48,500 |
| 4 m wide × 5 m deep (20 m²) | £49,500–£80,500 |
| 4 m wide × 6 m deep (24 m²) | £59,500–£96,500 |
These are guide ranges; the written quote after the survey is the figure that counts.
Do you need planning permission for a semi-detached rear extension in Barnet?
Whether your semi-detached rear extension in Barnet needs a planning application depends on its size, your house and any local restrictions.
In England a single-storey rear extension can often be built under permitted development: up to 3 metres beyond the original rear wall of an attached house, or 4 metres on a detached house, no higher than 4 metres, with eaves no higher than 3 metres if any part is within 2 metres of a boundary.
A two-storey rear extension can be permitted development in England only if it projects no more than 3 metres, stays at least 7 metres from the rear boundary, matches the existing roof pitch and has obscure-glazed upper side windows. In practice most double-storey rear extensions go through a householder planning application.
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.
Conservation areas, National Parks, National Landscapes and the Broads restrict permitted development, and listed buildings always need listed building consent. We check your house's planning history and any conservation area before drawing, so the route is clear before you spend on plans.
What are homes in Barnet like to extend?
Barnet is mostly 1930s semis, short terraces and post-war houses, so full-width single-storey and two-storey rear extensions are realistic on many plots. Some later estates had permitted development rights removed by condition, so we check the planning history first.
How a semi-detached rear extension in Barnet comes together
Survey visit
We visit free of charge, measure up, check access, drainage and neighbours' extensions, and note what you want the room to do.
Drawings and budget
Floor plans and elevations for the options, each with a guide price.
Approvals
Permitted development check, prior approval or planning application, then Building Regulations drawings and structural calculations, plus party wall notices where they apply.
Fixed price and build
A written price for the agreed design, a start date and a named contact through the build, ending with the building control completion certificate.
Semi-detached rear extensions near Barnet
From Barnet, the nearest places we also cover are New Barnet (1.1 miles) and Totteridge (1.2 miles).
- Semi-detached rear extension in New Barnet
- Semi-detached rear extension in Totteridge
- Semi-detached rear extension in East Barnet
- Semi-detached rear extension in Hadley Wood
- Semi-detached rear extension in Cockfosters
Other work in Barnet:
FAQ
Semi-detached rear extension questions in Barnet
Will I need a structural engineer?
Yes for the beam over the new opening and usually the foundations; we arrange them and their calculations go to building control.
Can you match the brick or stone on my Barnet house?
We source the closest match and show you samples before ordering; reclaimed materials are often the best match on older houses.
Can I match pebbledash or render?
Yes. Many semis are refinished with new render across the whole back elevation so old and new match.
Can I get a price without a visit?
Our online guide-price tool gives a range in a couple of minutes. A written price needs a survey.
How long does a rear extension take to build in Barnet?
Most single-storey rear extensions take 10 to 16 weeks on site and two-storey extensions 16 to 26 weeks, after design and approvals.
Do you handle building control in Barnet?
Yes. We apply to the council or a registered building control approver and hand over the completion certificate.