House Extensions Barnet
Single storey rear and double storey extensions in Barnet, planning, structure and build under one contract.
- Rated 4.9 from 31 reviews on MyBuilder
- Single-storey rear extension from £40,000
- Free site survey, itemised quote
GS Renovation plans and builds extensions across Barnet, adding space to the 1930s semis and interwar suburban houses found across Finchley, Mill Hill and Edgware. We handle foundations, steelwork, roofing and the full fit-out, and guide you through permitted development or a planning application to Barnet Council.
In Barnet, a single-storey rear extension typically starts from £40,000, or £2,000 to £2,800 per m² (indicative London ranges, Architecture for London, Resi, MyBuilder and Checkatrade, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Barnet: the structural engineer we appoint designs the structure, we build it, and building control signs it off.
Price guide
| Work | Indicative London range |
|---|---|
| Single-storey rear extension | from £40,000 |
| Rear extension, per m² | £2,000 to £2,800 |
| Side return, per m² | £2,400 to £3,200 |
| Wraparound, per m² | £2,400 to £3,200 |
| Double storey, per m² | £1,800 to £2,600 |
| Basement extension | see the basement page |
Indicative London ranges (Architecture for London, Resi, MyBuilder and Checkatrade, 2026), not a quotation. Prices checked September 2026. Full breakdown: Extension Costs & Planning.
Quick estimate for Barnet
Barnet range: choose above
Rear and side-return extensions in Barnet
Barnet's interwar semis were built with side access down one flank, which makes them suited to side and wrap-around extensions as well as the more common single and double storey rear additions. A kitchen extension, opening the old kitchen into a new rear extension, is the most popular project we build across Finchley, Hendon and Mill Hill, creating the open-plan kitchen-diner that these 1930s layouts naturally lack.
Every extension starts with proper groundworks. We dig and pour foundations to suit the ground conditions and any nearby trees, common on the leafy plots around Mill Hill and Hadley Common, then build up in blockwork or brick to match the existing house. Steel beams tie the new opening to the old structure, and we complete the roof, glazing, insulation, plastering, electrics and decoration as one continuous job.
Housing in Barnet
Take the 160,480 or so homes the valuation list gives Barnet: 50% flats, 50% houses, 20% from before 1919, 34% interwar and 46% post-war. Many homes here are flats, and a flat in Barnet has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent.
Two consents in Hampstead Garden Suburb and the CIL step for extensions
In Hampstead Garden Suburb Conservation Area, building an extension needs consent from both Barnet Council and the Hampstead Garden Suburb Trust. The two decisions are separate, so neither one on its own lets work start, and both should be applied for with the same drawings. The width is the usual sticking point: the Suburb's design guidance says rear extensions should generally not be wider than half the width of the rear elevation and, in most instances, less. That generally rules out the full-width kitchen extension seen on semis elsewhere in Barnet, so the design starts from a narrower footprint and a shorter opening into the house.
The Community Infrastructure Levy is the other step that catches people out. Barnet Council was one of the first London authorities to adopt and implement it, in May 2013, and its revised charging schedule came into effect on 1 April 2022. A large householder extension can fall within the levy, and any exemption has to be claimed from the council before work starts on site, with the commencement paperwork in order. Starting first puts the exemption at risk, so we build that step into the programme for a Barnet extension before the groundworks date is fixed.
Permitted development or planning in Barnet
Many single storey rear extensions on Barnet semis fall under permitted development, but this is not guaranteed. Larger builds, most double storey extensions, and any work to the front usually need a full planning application to Barnet Council. Homes within Hampstead Garden Suburb, a designated conservation area, face tighter controls, and some streets carry Article 4 directions that remove particular permitted development rights, so check the council's Article 4 list for your address.
We assess your property early and tell you honestly which route applies, then prepare drawings and manage the submission. Separately, the build must meet building regulations, with inspections at foundations, damp course, steelwork and completion. Where the extension sits on or near the boundary you share with a neighbour, the party wall notices of the 1996 Act apply. You serve them as building owner, we give you the drawings they need, and we build the notice period into the programme so nothing stalls on site.
Kitchen extensions in Barnet
60% of the houses in Barnet are semi-detached or detached, which usually leaves room for a kitchen extension across the full rear width, with a steel beam over the opening into the house. The fit-out is priced on its own page, kitchen renovation in Barnet; the build figures are in the table above.
Double storey extensions in Barnet
Under permitted development a two-storey rear extension can go no more than 3 metres beyond the original rear wall and must stay at least 7 metres from the rear boundary, and in a conservation area it is not permitted development at all. Many gardens are too short for the 7 metre rule, so a double storey extension in Barnet often needs planning permission from Barnet Council. With 30% of homes here semi-detached or detached, the side of the house is often an option too. The national Planning Data service returns 16 conservation area results for the London Borough of Barnet, including Railway Terraces (council source). Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Planning applications and permitted development assessments
- Drawings and the structural engineer's design coordinated for you
- Single and double storey extensions
VOA Council Tax stock of properties, March 2025, for all 42 statistical areas in Barnet. Counts rounded by the VOA.
Why Choose GS Renovation in Barnet
Barnet homeowners choose GS Renovation because one team takes the extension from first drawings to final decoration, including foundations, steel, roofing and services. We know how the borough's interwar plots behave, how Barnet Council handles planning, and where conservation and Article 4 rules bite. Our founder's 30+ years of building means realistic timescales and no nasty surprises.
- Drainage diverted or built over with the right approval in place
- Programme planned around party wall notice periods before excavation near a neighbour
- Straight advice on what is and is not worth spending money on
Reviewed jobs near Barnet
2 MyBuilder reviews from Barnet, with each customer's own job title:
- Install new kitchen, Barnet, 15 Apr 2022 (5 out of 5)
- Bathroom Refurbishment, Barnet, 14 Oct 2021 (5 out of 5)
Read all 31 on our reviews page.
Built a new extension at rear of property. Laid foundations, drainage, raised floor, new roof and completed all fixtures and interior decoration…
Saiid did a complete refurbishment of our small bathroom. This involved ripping out the existing bath/shower, basin, toilet, pipework, and tiles and…
The kitchen has been fitted to the high standard. Saaid was polite, professional, tidy, he pays attention to a little details that make huge…
FAQ
Frequently Asked Questions about House Extensions Barnet
What is the going rate for house extensions around Barnet?
House extensions around Barnet typically costs £2,000 to £2,800 per m² for a rear extension (indicative), but scope varies more than the market does. Two Barnet jobs of the same size can be different work, because the drainage run under the footprint decides the foundations. GS Renovation surveys and prices each on its merits at EN5, with the Barnet Council building control fee shown separately.
What extension suits the housing across Barnet?
A single storey rear extension in most cases, sometimes with a side infill. Much of the stock across Barnet is semi detached with a reasonable garden and a gap to one boundary, so building out at the rear adds usable space without taking the whole plot. Two storey extensions are possible where the plot and the roof arrangement allow. What your garden can spare is usually the deciding factor.
How do trees affect foundations for a Barnet extension?
They can require considerably deeper foundations where the ground is clay. A tree near a Barnet property draws moisture from the soil, and the ground beneath a shallow foundation then moves as that moisture changes with the seasons. The engineer takes the species, the distance and the mature height into account when setting the depth. Removing the tree instead can cause the ground to swell, which is a different problem.
Can a Barnet extension contain a bathroom or utility room?
Yes, and the drainage decides where. Putting a WC or a utility into a Barnet extension means reaching the existing soil stack with adequate fall, and a long shallow run will not clear reliably. Where the stack cannot be reached a new connection or a pumped arrangement is designed. Mechanical ventilation is required in both rooms, so a duct route to outside is settled with the layout.
Can a Barnet house stay occupied during an extension?
For most of the build, yes. A rear extension at your Barnet property is largely constructed outside the existing walls, so you keep the house usable until the point where the two are joined and the rear wall is opened. That period is the disruptive one, and we keep it short by preparing everything first. Kitchens are the exception, because the room is usually out of use for weeks.
Does an extension affect the energy rating of a Barnet house?
It usually improves it slightly, because the new structure has to meet current standards. An extension at a Barnet property is built with insulation, glazing and airtightness well ahead of the original house, so the average performance rises even though the older fabric is unchanged. Where an assessment is needed for a sale or a mortgage, it is carried out after completion rather than before.
Do the Article 4 rules on The Burroughs in Hendon affect a rear extension?
At the addresses covered, yes. If the house is one of 63-77 (odd) The Burroughs or 1-8 Burroughs Gardens, the direction removes permitted development rights for the enlargement, improvement or other alteration of a dwellinghouse. A rear extension there needs a planning application to Barnet Council even where the same extension on another street would not. Allow for the decision period before booking groundworks or ordering steel.
What does Barnet's Totteridge appraisal mean for extending a smaller house there?
Barnet's Totteridge Conservation Area appraisal records continuous development pressure to enlarge smaller properties by extension, or by demolition and rebuild. It treats those smaller houses as characteristic of the area, so an application to enlarge one should show how the original house stays readable, with a lower ridge, set-back walls and matching materials. Existing and proposed drawings side by side make that case, and they are worth preparing before a structural scheme is priced.
Which plan does Barnet Council judge an extension application against now?
The adopted plan in force on the day the application is decided. The national Planning Data record for the Barnet Local Plan document gives a start date of 2025-03-04, so check that any planning statement for the extension quotes the current plan rather than older borough policy. Refusals or approvals on neighbouring houses from before that date may rest on policies that have since changed, which makes them a weaker guide than they look.
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