Area guide · EN5 & EN4
House Extensions in Barnet (EN5 & EN4)
Planning a house extension in Barnet? We design, gain planning permission and build extensions and loft conversions across High Barnet, East Barnet and New Barnet. Most single-storey rear extensions here cost £45,000–£90,000 to build, the majority go through Barnet Council under permitted development, and the most-approved project type in the borough right now is the hip-to-gable loft conversion — a perfect match for Barnet's 1930s semis. Book a free site visit and we'll tell you exactly what's possible on your street.
Live planning data
What Barnet Council is actually approving right now
We track every residential planning decision across North London — so instead of guessing what your council will accept, you can see it. In the most recent decision period, these are real schemes Barnet Council approved:
- Haslemere Avenue, EN4 — roof extension with hip-to-gable, replacement rear dormer with Juliette balcony and a new side gable window (lawful development)
- Jackson Road, EN4 — hip-to-gable roof extension, rear dormer and two front rooflights (lawful development)
- Rosslyn Avenue, EN4 — double hip-to-gable extension with rear dormer and three front rooflights (lawful development)
- Heddon Court Avenue, EN4 — rear dormer with Juliette balcony, front rooflight and new side gable window (approved subject to conditions)
- East Walk, EN4 — single-storey rear extension with a roof lantern and patio alterations (approved subject to conditions)
- Ashurst Road, EN4 — part single, part two-storey side and rear extension with rooflights (approved subject to conditions)
- Byng Road, EN5 (High Barnet) — single-storey rear extension replacing an existing conservatory (approved)
- Grasvenor Avenue, EN5 — rear garden room (approved)
- Willenhall Avenue, New Barnet — rear outbuilding (approved)
Two things jump out of the data. First, lofts dominate Barnet approvals — hip-to-gable conversions with rear dormers are going through repeatedly, because the borough's huge stock of hipped-roof 1930s semis is made for them. Second, single-storey rears with roof lanterns are sailing through as lawful development or with light conditions. If your project looks like the ones above, you're in well-trodden territory — and we design to that grain.
Source: public Barnet Council planning decision records. Examples show what's being approved locally; they're not our projects, and every application turns on its own details.
Local knowledge
Barnet's housing stock — and what works on each
Barnet isn't one market; it's three or four, and the right extension depends on which street you're on.
The 1930s semi belt (East Barnet, New Barnet, Oakleigh Park, parts of EN5). This is classic Metroland: bay-fronted, hipped-roof semis with decent gardens and side passages. The two highest-value moves here are the hip-to-gable loft with rear dormer — which converts the wasted hip into a full double bedroom and en-suite, typically £55,000–£90,000 — and the single-storey rear extension opening the kitchen into the garden, typically £45,000–£90,000 depending on size and spec. The approvals list above shows Barnet Council passing both, street after street.
Victorian and Edwardian terraces (High Barnet, around Wood Street and the High Street). Narrower plots with rear additions — the play here is the side-return extension (£35,000–£65,000), reclaiming the dead alley beside the kitchen to create a full-width kitchen-diner, often combined with a rear extension as a wrap-around. Party wall agreements with both neighbours are usually needed; we manage that process.
Detached and semi-rural Barnet (Arkley, Hadley, the green-belt edge). Bigger plots take double-storey rear extensions (£75,000–£160,000) and substantial wrap-arounds. Some of this edge sits in the green belt, where volume limits bite — we check before you fall in love with a scheme.
Monken Hadley and the conservation streets. Monken Hadley and Wood Street are conservation areas, with some of Barnet's most beautiful — and most protected — houses. Permitted development rights are restricted, materials matter, and rooflights and dormers are scrutinised. Extensions absolutely still happen here; they just need conservation-literate design. That's a service, not a problem.
Every street is different. That's the point.
We design to 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 Barnet in 2026
These are realistic all-in build ranges for Barnet — labour and materials to a good standard, excluding VAT, professional fees and kitchen fit-out:
| Extension type | Typical 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 |
As a rule of thumb, Barnet build costs run £2,800–£4,200 per square metre — North London rates, 20–40% above the national average, driven by London labour and the care period properties need. A 20m² rear extension typically lands at £60,000–£80,000 for the build. We quote fixed, itemised prices after a free site visit, so the number you sign is the number you pay.
Permissions, handled
Planning permission in Barnet — what you need to know
Most Barnet extensions don't need a full planning application. Permitted development covers single-storey rear extensions up to 3m deep on semis and terraces (4m on detached homes), and up to 6m/8m under the larger home extension scheme with prior approval. Loft conversions enjoy a generous volume allowance — which is exactly why Barnet's approvals list is full of hip-to-gable schemes done as lawful development.
Where you do need permission: double-storey and wrap-around extensions, anything in the conservation areas (Monken Hadley, Wood Street and others), flats and maisonettes, and homes where previous owners have already used up permitted development rights. Barnet aims to decide standard householder applications in around eight weeks.
Party walls: most Barnet homes are semi-detached or terraced, so the Party Wall Act applies to the majority of projects — budget £1,000–£2,500 per affected neighbour if surveyors are appointed, and start the conversation early. We prepare the notices as part of the job.
Our approach: we design to what Barnet Council demonstrably approves — the data above isn't decoration, it's how we de-risk your application. Where a Lawful Development Certificate is the smarter route, we'll tell you and obtain it, so your extension is bulletproof when you sell.
How it works
How it works
- Free site visit — we walk your Barnet property, talk through what you want, and give honest guidance on feasibility, cost and the planning route.
- Design & drawings — detailed plans and 3D visuals tailored to your house and how you live.
- Planning, handled — we prepare and submit everything to Barnet Council and manage it to decision.
- Fixed-price build — our vetted North London team delivers, with building control sign-off and a tidy handover.
Our work
Recent work near Barnet
Our build team's recent North London projects include 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. Ask to see relevant examples at your site visit — we'll show you projects that match what you're planning.
Questions, answered
Barnet extension FAQs
How much does a house extension cost in Barnet?
Typically £45,000–£90,000 for a single-storey rear extension build, £55,000–£90,000 for a hip-to-gable loft, and £75,000+ for double-storey schemes — excluding VAT and fees. Barnet sits on North London rates of roughly £2,800–£4,200/m². We give a fixed, itemised quote after a free site visit.
Do I need planning permission for an extension in Barnet?
Often not — standard rear extensions and most loft conversions proceed under permitted development, and Barnet's recent approvals show hip-to-gable lofts repeatedly going through as lawful development. You will need permission for two-storey schemes, wrap-arounds, and anything in conservation areas like Monken Hadley or Wood Street.
How long does Barnet Council take to decide?
Around 8 weeks for a standard householder application once validated. Design and drawings before that typically take 4–8 weeks; lawful development certificates are usually quicker.
What's the best extension for a 1930s semi in East Barnet or New Barnet?
The data answers this one: a hip-to-gable loft conversion with rear dormer (two new bedrooms up top), a single-storey rear extension for an open-plan kitchen-diner, or both phased together. They're the most-approved schemes in the borough for a reason.
Do you cover all of Barnet?
Yes — High Barnet, Chipping Barnet, East Barnet, New Barnet, Oakleigh Park, Arkley, Monken Hadley and the Hadley Wood border, plus neighbouring Whetstone, Totteridge and Cockfosters.
Is my house in a conservation area?
Barnet has a number of conservation areas — Monken Hadley and Wood Street are the best known. We check your address against the council's conservation map as part of the free consultation, before any design work starts.
Nearby areas we cover
Ready to see what's possible on your street?
Free site visit anywhere in Barnet, honest feasibility advice and a fixed, itemised price — design, planning and build handled end to end.
Or call us — 020 3051 9430