Area guide · EN4–EN5
House Extensions in New Barnet (EN4 & EN5)
Planning a house extension in New Barnet? We design, gain planning permission and build extensions and loft conversions across New Barnet — from the Victorian grid around the station to the 1930s avenues that filled in around it. Building a single-storey rear here generally runs to £45,000–£90,000, decisions rest with Barnet Council, and the dominant approval across EN4 right now is the hip-to-gable loft conversion, with garden buildings close behind. Arrange a free site visit and we'll give you chapter and verse on what your particular street allows.
Live planning data
What Barnet Council is actually approving right now
Residential planning decisions across North London get logged by us as they land — so you can see what Barnet is passing instead of guessing. In the most recent decision window, EN4 recorded six residential approvals, and these two sit in the New Barnet area:
- Willenhall Avenue, New Barnet — outbuilding in the rear garden (approved)
- 40 Jackson Road — hip-to-gable roof extension, rear dormer and two front rooflights (lawful development)
Step back and the postcode-wide pattern is unmistakable: hip-to-gable loft conversions dominate EN4's approvals, clearing again and again. Borough-wide, Barnet approved 63 residential schemes in the same two-week window.
Two useful lessons for New Barnet owners. First, the Jackson Road scheme — hip-to-gable, rear dormer, two front rooflights — is the exact template for the area's hipped-roof semis, and it cleared as lawful development rather than needing a full application. Second, Willenhall Avenue's outbuilding approval shows the garden-building route working here: a home office, gym or studio at the end of the garden, often achievable without a full planning application at all.
Source: Barnet Council's public decision lists. These examples chart the council's recent habits, not our own work — and remember that each application is weighed entirely on its own merits.
Local knowledge
New Barnet's housing stock — and what works on each
New Barnet is a railway suburb in the most literal sense — the Great Northern station arrived in 1850, decades before most of the streets — and the housing tells that story in layers.
The Victorian and Edwardian grid around the station. The first wave: bay-fronted terraces and villas on the streets closest to the line. The strongest moves are the side-return extension (£35,000–£65,000), turning the alley beside the kitchen into one wide kitchen-diner, the single-storey rear (£45,000–£90,000), and the two combined as a wrap-around (£70,000–£140,000). Victorian roof shapes vary, so loft feasibility is street-by-street — we check pitch and ridge height before promising anything.
The 1930s infill avenues. Between and beyond the Victorian grid came the hipped-roof semis — and this is hip-to-gable country, as 40 Jackson Road proves. A hip-to-gable loft with rear dormer (£55,000–£90,000) typically adds a double bedroom and en-suite, with front rooflights keeping the street elevation tidy, exactly as approved at Jackson Road.
Gardens with room to spare. New Barnet's plots often run long, which is why the garden building is quietly booming — Willenhall Avenue's approval being the latest local example. Garden rooms have their own permitted development allowance (single-storey, with height limits near boundaries), making them one of the fastest routes to serious extra space.
The larger homes towards the EN5 side. West towards High Barnet, plots and houses grow — supporting double-storey rears (£75,000–£160,000) and substantial side schemes for families planning to stay put for the long haul.
Every street is different. That's the point.
We design to New 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 New Barnet in 2026
Realistic New Barnet build budgets look like this — decent-spec labour and materials, with VAT, professional fees and the kitchen itself costed on top:
| Extension type | Typical New 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 |
Pricing here tracks the usual North London band of £2,800–£4,200 per square metre — multiply that out and a typical 20m² rear scheme needs a build budget running from the mid-£50,000s to the mid-£80,000s. Garden rooms price by specification, from simple insulated shells to fully plumbed studios. The quote you receive after the free site visit is fixed and itemised down to the line.
Permissions, handled
Planning permission in New Barnet — what you need to know
The permitted development routes work hard here. A semi or terraced house gets 3m of single-storey rear extension as of right and a detached house 4m — and with prior approval through the larger home extension scheme, those depths double to 6m and 8m. Lofts carry a generous volume allowance — which is why EN4's approvals are full of hip-to-gable conversions — and garden buildings have an allowance of their own, as Willenhall Avenue shows.
Note the phrase "lawful development" against 40 Jackson Road: the owners obtained formal confirmation that their loft needed no planning permission. That's a Lawful Development Certificate, and we recommend one for every PD project we build — it costs little, and it's the piece of paper that satisfies solicitors and surveyors when you sell or remortgage.
Full applications are needed for wrap-arounds, double-storey rears, flats, and homes where PD rights are already spent. For a standard householder application, Barnet's turnaround typically runs to about eight weeks.
Party walls: with terraces around the station and semis everywhere else, the Party Wall Act touches most New Barnet projects — budget £1,000–£2,500 per affected neighbour if surveyors are appointed. We prepare and serve the notices as part of the job, and we check your address against the council's conservation map before design starts.
How it works
How it works
- Free site visit — we come out to your New Barnet home, talk through the brief, and give you an unvarnished view of feasibility, budget and the right consent route.
- Design & drawings — measured plans and 3D visuals built around the house you have and the life you want in it.
- Planning, handled — whether it's a full submission to Barnet Council or certifying the lawful development route, we run the paperwork all the way to decision.
- Fixed-price build — delivery by our proven North London team, signed off by building control and handed over tidy.
Our work
Recent work near New Barnet
Recent work by our build crew around North London includes a 55m² garden room with kitchen and bathroom — proof of how far the garden-building format New Barnet loves can stretch — alongside a full house transformation taking a family home from 120m² to 360m² and an Edwardian conversion in Finchley. Raise it at the site visit and we'll talk you through whichever of these sits nearest to your own project.
Questions, answered
New Barnet extension FAQs
How much should I set aside for an extension in New Barnet?
Build costs sit at standard North London rates of roughly £2,800–£4,200/m² — so £45,000–£90,000 for a single-storey rear, £55,000–£90,000 for a hip-to-gable loft, £35,000–£65,000 for a side-return on the Victorian terraces. VAT and professional fees are on top; our quotes are fixed and itemised.
Do I need planning permission for a garden room or office in New Barnet?
Often not — outbuildings have their own permitted development allowance, and the recent Willenhall Avenue approval shows garden buildings going through locally. Size, height near boundaries and how much garden remains all matter, so we confirm your plot's position before designing.
What loft conversion suits my hipped-roof semi?
The one just confirmed at 40 Jackson Road: hip-to-gable with a rear dormer and front rooflights. It's the template for New Barnet's 1930s semis — typically a double bedroom plus en-suite, usually achievable as lawful development under the loft volume allowance.
Is a Lawful Development Certificate worth the bother if I don't need permission?
Emphatically yes. Jackson Road's owners secured one, and we obtain them as standard: the certificate proves your extension was lawful on the day it was built, which is exactly what a buyer's solicitor will demand years later. Skipping it saves pennies and risks pounds.
What works best on the Victorian terraces near the station?
A side-return extension, a rear extension, or both together as a wrap-around — these terraces were built with narrow back kitchens that open-plan living has outgrown. Party wall agreements with both neighbours are usually part of the package; we manage them.
How long does the whole process take in New Barnet?
Roughly: a few weeks for survey and design, around eight weeks for a Barnet householder decision (lawful development certificates are often quicker), then two to four months on site for single-storey work — longer for two-storey schemes. We give real programme dates with the quote.
Nearby areas we cover
Ready to see what's possible on your street?
Free site visit anywhere in New Barnet, honest feasibility advice and a fixed, itemised price — design, planning and build handled end to end.
Or call us — 020 3051 9430