Area guide · N8
House Extensions in Hornsey (N8)
Planning a house extension in Hornsey? We design, gain planning permission and build extensions and loft conversions across Hornsey's Victorian streets — the old core around St Mary's church tower, the avenues running up towards Alexandra Palace, the lanes along the New River path. Most single-storey rear extensions here cost £45,000–£100,000 to build, applications go to Haringey Council, and the ground-floor side infill is the signature move on Hornsey's tighter terraces. Book your free site visit and we'll set out what's realistic on your road, house by house.
Planning in Hornsey
What Haringey Council has recently approved in Hornsey
Haringey's decisions are published, which means Hornsey owners can read the council's actual behaviour instead of guessing at it. The list below comes from Haringey's Hornsey ward.
It's a fair cross-section of how tight terraces extend: infills beside the back addition, full-width rears, roof extensions over the outrigger, and now and then a deep rear extension through the larger-home prior approval. Hornsey's terraces are tighter than neighbouring Crouch End's, so the side passage is the most valuable dead space in the house: infilling it transforms the kitchen without sacrificing an inch of garden. Read the refusals as closely as the approvals: on tight terraces, a roof terrace over the back addition raises overlooking questions that the extension underneath it usually doesn't.
Recent planning decisions around Hornsey
Extension, loft and basement applications decided in Haringey's Hornsey ward, 23 Sep 2025 to 22 Sep 2026.
The newest decisions in those wards
- RefusedSep 2026
The Gardens, N8
Roof enlargement with hip to gable and rear dormer extensions, incorporating new roof terrace at second floor level over existing outrigger.
HGY/2026/1585 · Haringey CouncilHouseholder application
- ApprovedAug 2026
Rathcoole Avenue, N8
Outrigger roof extension.
HGY/2026/2179 · Haringey CouncilLawful development certificate
- ApprovedAug 2026
South View Road, N8
Erection of part single part two-storey rear side infill extension.
HGY/2026/1688 · Haringey CouncilHouseholder application
- ApprovedAug 2026
Boyton Road, N8
Erection of a single-storey rear extension at ground floor level.
HGY/2026/1689 · Haringey CouncilHouseholder application
- ApprovedJul 2026
South View Road, N8
Addition of a roof extension over the rear outrigger adjoined to the existing rear main roof dormer and replacement and relocation of 2x…
HGY/2026/1588 · Haringey CouncilLawful development certificate
- ApprovedJun 2026
Linzee Road, N8
Erection of single storey extension which extends beyond the rear wall of the original house by 6m, for which the maximum height would be…
HGY/2026/1305 · Haringey CouncilPrior approval, larger home extension
- ApprovedMay 2026
Ferrestone Road, N8
Erection of single storey ground floor infill and rear extension.
HGY/2026/0900 · Haringey CouncilHouseholder application
- ApprovedMay 2026
Hermiston Avenue, N8
Demolition of the ground floor garage and erection of a two storey side extension with rear terrace, a single storey rear extension, and a…
HGY/2026/0477 · Haringey CouncilHouseholder application
Source: GLA Planning London Datahub, 23 Sep 2025 – 22 Sep 2026. Data updated September 2026. This list last changed 23 September 2026. The datahub can lag a council’s own register by a few weeks.
These are council decisions on applications in these wards, shown as local planning context. They are not necessarily projects undertaken by us, and they are not our approval rate. Planning outcomes depend on your specific property and proposal.
Local knowledge
Hornsey's housing stock — and what works on each
Hornsey is the original village in this corner of N8 — older bones than Crouch End, tighter streets, gentler prices. Different streets reward different moves.
The old core around St Mary's church tower. Compact Victorian terraces where every metre counts. The old village core along Hornsey High Street, where the tower stands, is the Hornsey High Street conservation area, designated in 1980. The side infill (£35,000–£70,000) is the highest-value move, turning a dark corridor kitchen into a full-width, light-filled room. Where the budget stretches, adding a modest rear extension creates an L-shaped kitchen-diner.
The avenues towards Alexandra Palace. Slightly wider Victorian and Edwardian houses. Side infill plus rear extension works well here, as does the loft conversion with rear dormer (£55,000–£100,000) for a bedroom and en-suite with Ally Pally views from the right streets.
The High Street and New River quarter. A more mixed bag — terraces, twentieth-century infill and newer builds near the New River path. Straightforward rear extensions (£45,000–£100,000) and the occasional garage conversion (£18,000–£38,000) where garages exist.
Flats and conversions. Hornsey has its share of converted houses. Flats have no permitted development rights, so every extension or dormer needs a full application — workable, but factor in the timeline.
Every street is different. That's the point.
We design to Hornsey'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 Hornsey in 2026
Hornsey builds at North London baseline rates with a modest uplift on the prettiest streets — gentler than Crouch End, same builders, same materials. The table gives realistic all-in build ranges; VAT, professional fees and kitchen fit-out are extra:
| Extension type | Typical Hornsey cost | On-site time | Usual planning route |
|---|---|---|---|
| Side-return extension | £35,000 – £70,000 | 2–3 months | Often permitted development |
| Single-storey rear | £45,000 – £100,000 | 3–4 months | Often permitted development |
| Kitchen extension (incl. mid-range kitchen) | £55,000 – £120,000 | 3–4 months | Often permitted development |
| Loft conversion + rear dormer | £55,000 – £100,000 | 6–10 weeks | Usually permitted development |
| Wrap-around extension | £70,000 – £155,000 | 4–6 months | Full application |
| Double-storey rear | £75,000 – £175,000 | 5–7 months | Full application |
| Garage conversion | £18,000 – £38,000 | 4–6 weeks | Usually permitted development |
Hornsey's going rate is £2,800–£4,600 per square metre — the £2,800–£4,200 North London baseline with up to 10% added in the premium pockets. A 16m² side infill, Hornsey's signature project, works out at roughly £45,000–£74,000 on those rates. After the free visit we set a fixed price, itemised throughout, and we hold it — the figure you sign against never creeps.
Permissions, handled
Planning permission in Hornsey — what you need to know
Much of Hornsey extends under permitted development. Semis and terraces can push 3m to the rear — detached houses 4m — without a full application, and the larger home extension scheme's prior-approval route raises those limits to 6m and 8m. Add the generous loft volume allowance and you can see why rear dormers keep appearing across N8.
Side extensions — Hornsey's speciality — are more nuanced. Some qualify under permitted development (single-storey, limited width); many here need a full application because of how tightly the terraces sit. A full application with considered detailing is a well-used route for them in N8, and we confirm the right path for your house before a single line is drawn.
Conservation status: four conservation areas sit in Hornsey ward — Hornsey High Street, Hillfield (built around Hillfield Avenue), the Campsbourne cottage estate, and the Hornsey Water Works and Filter Beds along the New River, the last three all designated in 1994. None carries an Article 4 direction on Haringey's list, but inside each of them the national conservation-area rules take side extensions, dormers and the larger-home route out of permitted development and raise the design bar. Our borough-by-borough North London guide covers how Haringey's rules sit beside the neighbouring boroughs'.
Haringey works through a standard householder application in something like eight weeks. Terraced building means party walls: budget £1,000–£2,500 per affected neighbour if surveyors are appointed — we prepare the notices as part of the job. And wherever works proceed under permitted development, we recommend a Lawful Development Certificate, so everything is watertight when you sell.
How it works
How it works
- Free site visit — we come to your Hornsey terrace, size up the side passage and the roof, and tell you honestly what works and what it will cost.
- Design & drawings — careful plans and 3D visuals that respond to your house's footprint and your household's habits.
- Planning, handled — application drafted, submitted to Haringey Council and chased by us until the decision is in.
- Fixed-price build — our vetted North London tradespeople deliver, building control signs off, and the handover is spotless.
Our work
Recent work near Hornsey
For Hornsey owners, the recent job we point to is a full house transformation in Hadley Wood, taking a family home from 120m² to 360m² — a bigger canvas than a terrace, but the same care over structure and finish. See the Hadley Wood project before the visit.
Questions, answered
Hornsey extension FAQs
Is it cheaper to build in Hornsey than Crouch End?
Slightly, yes. Hornsey runs from baseline to about 10% over, where Crouch End carries a 10–15% premium — same trades, same materials, gentler postcode pressure. On a typical rear extension that's a few thousand pounds' difference.
My terrace is narrow — will a side infill really make a difference?
It's usually the first move worth pricing on a tight Hornsey terrace. You're capturing space you already own — the dead passage beside the kitchen — and turning a corridor room into a proper family kitchen.
Will a side extension in N8 need planning permission?
Sometimes not — single-storey side extensions within strict size limits can be permitted development — but on Hornsey's tighter plots many need a full application. We confirm the route for your address before design starts, so there are no surprises.
What's the realistic planning timeline with Haringey?
Around eight weeks for a householder decision once the application is validated, with certificates of lawfulness usually faster. Add 4–8 weeks before that for design and drawings done properly.
Can I convert the loft on a Hornsey terrace?
Almost always — loft conversions enjoy a generous volume allowance under permitted development, and a rear dormer is the standard approach. The structural solution depends on your roof's build-up, which we assess at the site visit.
How do I know if my street has conservation status?
Haringey's interactive conservation map shows the boundaries; in Hornsey the ones to check are Hornsey High Street, Hillfield, Campsbourne and the Water Works and Filter Beds. We check your address against it as part of the free consultation, before any design work starts — it determines whether permitted development applies or a full application is needed.
What we build in Hornsey
The same team designs, gets planning and builds — one fixed, itemised price whichever route your Hornsey project takes.
Nearby areas we cover
What clients say
Rated 5.0 on Google
“The Extension Company built a 5m single storey rear extension on our Victorian terrace in Crouch End. Went down the permitted development route so no planning application needed, which they explained up front and saved us months. Kitchen-diner now opens onto the garden with sliding doors. £87k all in, matched the quote.”
“From the initial site visit onwards to my property in Barnet, we felt that the team actually listened to what we wanted. They suggested a few changes to the layout that we hadn't considered, and those changes have made a huge difference. Would definitely use again and recommend”
“Used The Extension Company for a loft conversion on our semi detached in Barnet and couldn't be happier. They explained what was possible at the first visit, sorted the planning side, and gave a fixed price with no surprises at the end. The hip-to-gable and rear dormer gave us a big double bedroom with an en-suite. Tidy, professional and finished on schedule. Would recommend to anyone in North London thinking about a loft conversion.”
“We had been putting off our loft conversion for years because the whole process felt overwhelming. The team made it much easier than expected and handled the drawings, planning and build for us. We now have a lovely extra bedroom and shower room.”
“Our wrap-around extension has completely transformed the ground floor. We now have the open plan kitchen and family space we wanted without losing all of the garden. Thanks to everyone involved.”
“Really pleased with the work from The Extension Company. We had our extension done in Hampstead and the whole experience was excellent. Great communication from start to finish, The quality of the finish is excellent and we’re really happy with the result. Would definitely recommend them if you’re thinking about an extension.”
Reviews shown word for word from our Google profile. See 9 more client reviews · Read all 16 reviews on Google
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