Area guide · N12
House Extensions in North Finchley (N12)
Planning a house extension in North Finchley? N12 is a patch we know street by street — the terraces off Ballards Lane, the 1930s semis beyond Tally Ho corner, Woodside Park's leafier grid — and we handle the whole journey: design, permission, build. Costs first: a single-storey rear typically builds for £45,000–£90,000, with Barnet Council deciding the application. Encouragingly, the latest N12 approvals cover the full compass — a rear dormer, a part two-storey side-and-rear scheme, and two front extensions. Get a free site visit in the diary and we'll translate all of that into what your own house can do.
Live planning data
What Barnet Council is actually approving in North Finchley right now
Rather than guess at the council's mood, we read it: as each North London residential planning decision is issued, it goes into our records. The most recent decision period brought approvals for three N12 schemes:
- 19 Avondale Avenue, N12 — roof extension with rear dormer and Juliette balcony (approved)
- 173 Torrington Park, N12 — part single-storey, part two-storey side and rear extension, plus a single-storey front extension (approved)
- 70 Friern Watch Avenue, N12 — single-storey front extension with a pitched roof (approved)
Borough-wide, Barnet approved 63 residential schemes in the same fortnight — and across the borough as a whole, hip-to-gable loft conversions and single-storey rear extensions dominate that list.
Two things stand out in the N12 set. First, owners here are extending in every direction — up (Avondale Avenue's dormer with its Juliette balcony), out and sideways (Torrington Park's multi-part scheme), and even forwards. Second, front extensions — which almost always need full permission — featured twice and passed twice. A well-proportioned front addition with a pitched roof is clearly winnable in N12, which surprises plenty of owners who'd written the idea off.
Source: the planning decisions Barnet Council publishes. These are other people's projects, cited purely to show what's passing locally — and what passed for them doesn't bind your case, which will turn on its own details.
Local knowledge
North Finchley's housing stock — and what works on each
North Finchley is two markets stitched together at Tally Ho corner — Victorian terrace streets on one side, Metroland semis on the other — with Woodside Park adding a leafier third.
The Victorian terraces off Ballards Lane. Behind the High Road and the artsdepot, the terrace streets respond to two classic moves. First, a side-return extension (£35,000–£65,000): the kitchen swallows the alley beside it and comes out a full-width kitchen-diner. Second, a loft conversion with rear dormer, supplying the bedroom and en-suite that turn a two-up-two-down into a family home.
The 1930s semi grid. Here the bay-fronted, hipped-roof semis take over, and with them the borough's single most-approved scheme: the hip-to-gable loft with rear dormer (£55,000–£90,000). Pair it with a single-storey rear (£45,000–£90,000) that opens the kitchen to the garden and you've made the two highest-percentage plays available in Barnet. Houses like these are precisely where the council's approval statistics come from.
Woodside Park. One grid over, the plots widen and the houses grow — large semis and detached homes with the elbow room for a double-storey rear (£75,000–£160,000) or a wrap-around (£70,000–£140,000) without feeling crowded.
The avenues — Torrington Park, Friern Watch Avenue and their neighbours. Generous Edwardian and interwar houses where multi-part schemes stack several moves into one consent — exactly what the approved part single-, part two-storey extension at 173 Torrington Park does.
Every street is different. That's the point.
We design to North Finchley's stock and to what the council demonstrably approves — not to a template. A free site visit tells you what your house can take.
Get my free estimateHonest numbers
What a house extension costs in North Finchley in 2026
Cost-wise, N12 is refreshingly unremarkable: standard North London rates, no postcode premium, no discount. What follows are believable build figures — labour and materials done properly, with VAT, professional fees and kitchen fit-out accounted for separately:
| Extension type | Typical North Finchley cost | On-site time | Usual planning route |
|---|---|---|---|
| Side-return extension | £35,000 – £65,000 | 2–3 months | Often permitted development |
| Single-storey rear | £45,000 – £90,000 | 3–4 months | Often permitted development |
| Kitchen extension (incl. mid-range kitchen) | £55,000 – £110,000 | 3–4 months | Often permitted development |
| Hip-to-gable loft + rear dormer | £55,000 – £90,000 | 6–10 weeks | Usually permitted development |
| Wrap-around extension | £70,000 – £140,000 | 4–6 months | Full application |
| Double-storey rear | £75,000 – £160,000 | 5–7 months | Full application |
| Garage conversion | £18,000 – £35,000 | 4–6 weeks | Usually permitted development |
The baseline arithmetic is £2,800–£4,200 per square metre, so a 23m² rear extension comes out around £64,000–£97,000 to build. We don't deal in moving targets: after the free site visit your quote is fixed and itemised, and that's the sum you'll actually pay.
Permissions, handled
Planning permission in North Finchley — what you need to know
A surprising amount of N12 work never sees a full planning application. As of right, permitted development allows a 3m-deep single-storey rear on semis and terraces and 4m on detached houses; clear the prior-approval hurdle of the larger home extension scheme and you can build to 6m, or 8m detached. Roof space is generous too — the loft volume allowance is one reason hip-to-gable schemes lead the borough's approvals.
Permission becomes essential for two-storey and wrap-around schemes (like the one approved at Torrington Park), for flats, and for front extensions, which sit outside permitted development entirely. The encouraging news from the latest N12 decisions is that well-designed front additions are getting through. As for conservation status, that's checked — address against council conservation map — during the free consultation, never assumed.
Decision timing? A standard householder application generally spends about eight weeks with Barnet once validated. Because N12 is a place of shared walls, party wall procedure features in most builds — set aside £1,000–£2,500 per affected neighbour where surveyors are appointed, and warm the neighbours up early; drafting and serving the notices is part of our job. Anything built under permitted development gets a Lawful Development Certificate from us as standard, so there's never an argument about it at sale time.
How it works
How it works
- Free site visit — we meet you at the house, whether that's a Ballards Lane terrace or a Woodside Park semi, and give a straight assessment of feasibility, cost and consent route.
- Design & drawings — drawings and 3D visuals that take their cue from your house's layout and how your family runs.
- Planning, handled — application drafted, submitted to Barnet Council and managed by us until the decision notice arrives.
- Fixed-price build — our long-standing North London team delivers the build, building control signs it off, and the handover is left immaculate.
Our work
Recent work near North Finchley
Lately the build team has completed a full house transformation taking a family home from 120m² to 360m², a 55m² garden room with kitchen and bathroom, and an Edwardian conversion in neighbouring Finchley — minutes down Ballards Lane. At your site visit, just ask: we'll bring whichever examples line up with your plans.
Questions, answered
North Finchley extension FAQs
What's the most-approved extension type around North Finchley?
Borough-wide, it's the hip-to-gable loft conversion and the single-storey rear — perfect for N12's 1930s semis. The latest local trio adds rear dormers, a multi-part two-storey scheme and two front extensions, so the council is clearly approving variety here.
Can I extend the front of my house in N12?
Front additions sit outside permitted development, so you'll need full permission — but two front extensions were approved in the latest N12 decisions, at Torrington Park and Friern Watch Avenue, both designed with pitched roofs. Done in proportion with the street, they pass.
What should a 1930s semi owner here budget?
£55,000–£90,000 for a hip-to-gable loft with rear dormer, £45,000–£90,000 for a single-storey rear — and doing both, phased, transforms the house for well under the cost of trading up in N12.
Do two-storey side and rear schemes get approved in North Finchley?
Yes — 173 Torrington Park's part single-, part two-storey side and rear extension is fresh proof. They need a full application, neighbour amenity is the key test, and budget £75,000–£160,000 for the build.
When could we realistically start on site?
Design and drawings take 4–8 weeks, Barnet's decision around eight more, and party wall notices run alongside — so most projects break ground 3–5 months after the first visit. Lofts done under permitted development can move faster.
Do you cover Woodside Park and the rest of N12?
All of it — Woodside Park, the Ballards Lane terraces, the avenues and everything between, plus neighbouring Whetstone and Friern Barnet. We're based in Cockfosters, a few minutes up the road.
Nearby areas we cover
Ready to see what's possible on your street?
Free site visit anywhere in North Finchley, honest feasibility advice and a fixed, itemised price — design, planning and build handled end to end.
Or call us — 020 3051 9430