Your local NW3 house extension builders
The NW3 postcode is home to some of North London's finest housing — from the grand Victorian villas of Belsize Park to the Edwardian terraces of Swiss Cottage, the period properties of Frognal and the cottages of Hampstead Village. Each has different structural requirements, different planning constraints, and different extension possibilities.
A house extension in NW3 typically adds £120,000–£300,000 to your property value. With our office on Finchley Road, we're the most local extension builders in the postcode.
We work closely with Camden Council's planning department and are experienced in both PD extensions and full planning applications across NW3. We handle all conservation area requirements, party wall agreements, and structural engineering.
NW3 areas we build in
The NW3 postcode covers diverse neighbourhoods. Here's how extensions differ across each area.
Hampstead Village
Period cottages and Georgian terraces in the conservation area. Extensions must be heritage-sensitive. We specialise in designs that complement the village character.
Belsize Park
Grand Victorian semis with large gardens — ideal for substantial rear and wrap-around extensions. Conservation area in parts requires careful design.
Swiss Cottage
Mixed stock including 1930s semis and mansion flats. Good-sized plots allow for generous rear extensions. Easier planning in most cases.
Frognal
Spacious Edwardian and Victorian properties with good garden depth. Two-storey extensions are feasible on many properties. Heritage-sensitive area.
Primrose Hill
Compact Victorian terraces where side-return extensions are transformative — turning narrow galley kitchens into open-plan living spaces.
Chalk Farm
Victorian terraces with side-return potential. Rear extensions create stunning kitchen-diners. Close to Camden Town conservation area boundaries.
"Hampstead Renovations transformed our cramped Victorian kitchen into a stunning open-plan kitchen-diner with bi-fold doors to the garden. The team managed all the planning and party wall issues, and the quality of the build was outstanding."Sarah & David MitchellHomeowners, Hampstead NW3
House extension costs in Hampstead
Realistic prices from recent Hampstead projects. We provide a fixed, all-inclusive quote after a site survey.
| Extension Type | Typical Range (Hampstead) |
|---|---|
| Single-storey rear extension | £55,000 – £90,000 |
| Side-return extension | £45,000 – £70,000 |
| Wrap-around (rear + side) | £80,000 – £130,000 |
| Two-storey rear extension | £100,000 – £170,000 |
| Kitchen extension (open-plan) | £60,000 – £100,000 |
| Glass box / frameless glazing | £70,000 – £130,000 |
| Orangery-style extension | £65,000 – £110,000 |
| Bi-fold / sliding doors | £3,500 – £8,000 |
| Underfloor heating | £2,500 – £5,000 |
All prices exclude VAT. Includes foundations, structural steelwork, brickwork, roofing, windows, electrics, plumbing, plastering, decoration and Building Control sign-off. Prices reflect Hampstead-area build costs as of 2026.
House extension FAQ — NW3
We cover the entire NW3 postcode: Hampstead, Belsize Park, Swiss Cottage, Frognal, Primrose Hill, Chalk Farm, South Hampstead, and all surrounding streets. Our office is on Finchley Road, NW3.
Side-return extensions are the most popular in NW3. They transform the narrow galley kitchens found in Victorian and Edwardian terraces into spacious open-plan kitchen-diners. Rear extensions with bi-fold doors are a close second.
Single-storey rear extensions up to 3m (terraced) or 4m (detached) often fall under Permitted Development. But many NW3 streets are conservation areas with restricted PD. Two-storey and side extensions usually need planning. We check your specific address.
Single-storey rear extensions in NW3 run £55,000–£90,000. Side-returns £45,000–£70,000. Wrap-around £80,000–£130,000. Two-storey £100,000–£170,000. All inclusive of structural work, finishes and Building Control.
Ground-floor flats with private garden access can sometimes be extended, subject to the lease terms, freeholder consent, and planning. We assess feasibility during a free consultation.
A single-storey rear extension takes 10–14 weeks on site. Wrap-around 14–18 weeks. Two-storey 16–22 weeks. Allow 4–12 weeks beforehand for design, planning and party wall.
Book a free extension consultation in NW3
We'll visit your NW3 property, assess the best extension options, check planning and conservation constraints, and provide a fixed price — completely free.
Unit 3, Palace Court, 250 Finchley Road, Hampstead, London NW3 6DN
Mon–Fri 9am–8pm · Saturday 9am–6pm · Sunday by appointment
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