Area guide · N11
House Extensions in Friern Barnet (N11)
Planning a house extension in Friern Barnet? From the 1930s semis along Friern Barnet Lane and around the village green to the Edwardian terraces towards New Southgate, N11 is home turf for our design, planning and build service. Two numbers frame most projects here: £45,000–£90,000 to build a typical single-storey rear, and one council — Barnet — making the call. Better still, the borough's two most-approved schemes right now, hip-to-gable loft conversions and single-storey rears, are tailor-made for Friern Barnet's housing. The free site visit comes first; that's where we tell you what your own street will carry.
Live planning data
What Barnet Council is actually approving right now
Guesswork is a poor way to start an extension, which is why we log every residential planning decision in North London and read the patterns before we draw. The latest two-week decision period saw Barnet Council approve 63 residential schemes — the busiest approvals pipeline in our patch — with two project types towering over the rest of the list:
- Hip-to-gable loft conversions with rear dormers — passing repeatedly, many as lawful development, because the borough's vast stock of hipped-roof 1930s semis suits them perfectly
- Single-storey rear extensions — going through under permitted development or with light conditions, street after street
Friern Barnet didn't happen to feature street-by-street in this particular fortnight's list, but the borough-wide pattern is precisely the point for N11: the houses along Friern Barnet Lane and around the village green are the same hipped-roof semis those approvals keep landing on. If your project looks like the borough's two favourite schemes, you're extending with the grain of what Barnet demonstrably passes.
Source: Barnet Council's published decision lists. We're describing the borough's recent behaviour, not showcasing our own jobs — and no decision above prejudges yours, because every application is weighed on its own facts.
Local knowledge
Friern Barnet's housing stock — and what works on each
Friern Barnet is quieter than its name-recognition neighbours — and that's exactly why the value is good. Four kinds of street, four different playbooks.
The 1930s semis around Friern Barnet Lane and the village green. Stand on the Lane and you're looking at the borough's favourite raw material: bay windows, hipped roofs, proper gardens. Up top, a hip-to-gable loft with rear dormer (£55,000–£90,000) trades the wasted hip for a genuine double bedroom with en-suite. At ground level, a single-storey rear (£45,000–£90,000) dissolves the wall between kitchen and garden. Barnet approves more of these two schemes than anything else — which makes them the lowest-friction extensions you can build in N11.
The Edwardian terraces towards New Southgate. Plots tighten near the station edge, and the smart money goes on the side-return extension (£35,000–£65,000) — the alley beside the kitchen becomes the missing width of a proper kitchen-diner — with dormer loft conversions the other proven move.
Princess Park Manor and the apartment stock. The converted Victorian hospital in its parkland is the local landmark — but apartments aren't extension candidates: flats have no permitted development rights, and managed estates bring their own consent layers. A good share of our N11 enquiries are owners trading an apartment for a nearby semi with extension potential priced in — we'll happily tell you what a house could become before you offer on it.
Post-war and infill streets. Where the plots square off and garages appear, the best pound-per-metre gains come from garage conversions (£18,000–£35,000) and simple, efficient rear additions.
Every street is different. That's the point.
We design to Friern Barnet'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 Friern Barnet in 2026
No postcode premium applies in Friern Barnet — you're buying construction at the honest North London baseline. The table gives genuine build figures: labour and materials to a good standard, with VAT, professional fees and the kitchen fit-out costed separately:
| Extension type | Typical Friern Barnet 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 |
Run the numbers at £2,800–£4,200 per square metre — the North London baseline — and a 21m² rear addition pencils out at roughly £59,000–£88,000 of build cost. When the quote comes, after a free site visit, it comes fixed and itemised: the total on page one is the total on the final invoice.
Permissions, handled
Planning permission in Friern Barnet — what you need to know
Start with the good news: a full application is often unnecessary in N11. Before any application is made, the permitted development rules give a semi or terrace 3m of single-storey rear extension and a detached house 4m; add prior approval under the larger home extension scheme and the limits move out to 6m and 8m. Lofts get a generous volume allowance of their own — the very reason hip-to-gable schemes lead Barnet's approval lists fortnight after fortnight.
Full permission still applies to: two-storey and wrap-around schemes, front extensions, and all flats and maisonettes — including everything at Princess Park Manor, where estate consents add a further layer. Conservation status we never assume: your address goes against the council's conservation map during the free consultation, because a conservation designation strips back permitted development rights.
On timing, budget about eight weeks from validation for Barnet to decide a standard householder application. Party walls come with the territory in a neighbourhood of semis and terraces — allow £1,000–£2,500 per affected neighbour if surveyors are appointed, and open the conversation over the fence early; the formal notices are ours to prepare and serve. And whenever a project runs under permitted development, we secure a Lawful Development Certificate, putting the works beyond question when you sell.
How it works
How it works
- Free site visit — we come to your N11 home, look at the roof, the garden and the side access, and give you a frank read on feasibility, cost and route.
- Design & drawings — a proper drawing package with 3D visuals, moulded to your house and the life inside it.
- Planning, handled — the Barnet Council paperwork is ours from first draft to final decision.
- Fixed-price build — our established North London team builds it through to building control sign-off and a tidy, complete handover.
Our work
Recent work near Friern Barnet
Three recent jobs give a flavour of the build team's range: 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. Whichever direction you're leaning, ask at the site visit and we'll talk you through the nearest equivalents.
Questions, answered
Friern Barnet extension FAQs
What is Barnet Council approving most at the moment?
Sixty-three residential consents went through in the latest two-week window, and two schemes dominate: hip-to-gable loft conversions with rear dormers, and single-storey rear extensions. Both are tailor-made for N11's 1930s semis.
How much is a hip-to-gable loft on a Friern Barnet semi?
£55,000–£90,000 for the build, typically 6–10 weeks on site, and usually achievable under permitted development thanks to the generous loft volume allowance. It converts the dead hip space into a full double bedroom with en-suite.
Will my N11 extension need a planning application?
Often not. Rear extensions up to 3m (4m detached) are permitted development, the prior approval route stretches that to 6m/8m, and most lofts fit the volume allowance. Two-storey schemes, wrap-arounds and front extensions need full permission — and we recommend a Lawful Development Certificate for anything built without one.
Can apartments at Princess Park Manor be extended?
Realistically, no — flats have no permitted development rights and the managed estate brings its own consent requirements. If you're weighing a move from an apartment to a nearby N11 house, we'll assess the house's extension potential before you commit.
What's the timeline from first call to finished extension?
Site visit within days; design and drawings 4–8 weeks; Barnet's decision around eight weeks (quicker for lawful development routes); then 2–4 months on site for a single-storey scheme or 6–10 weeks for a loft. Most families are in their new space within 6–9 months of picking up the phone.
Which areas around Friern Barnet do you cover?
All of them — North Finchley, Whetstone, New Southgate, Southgate, Muswell Hill, East Barnet and the Wood Green border — from our base in Cockfosters, ten minutes away.
Nearby areas we cover
Ready to see what's possible on your street?
Free site visit anywhere in Friern Barnet, honest feasibility advice and a fixed, itemised price — design, planning and build handled end to end.
Or call us — 020 3051 9430