Fixed price · Planning handled · Across London
North London projects designed, managed and built by our own team
House extensions in London, lofts and whole-house transformations: design, planning and build for one fixed, itemised price. Pine Grove Design & Build’s own team builds house extensions across North London, from Enfield and Barnet to Muswell Hill — see all areas we cover.
The Extension Company is the extensions arm of Pine Grove Design & Build Ltd — on North London projects the same team designs your extension, gets it through planning and builds it, with one point of contact throughout.
Lines open every day, 9am–8pm. If we're on site and miss you, we call back the same day.
North London first, then the rest of London
Enfield, Barnet and Haringey, with the Camden and Hackney edges. See house extensions across North London, borough by borough.
We cover the rest of London too. Find your area in the full list of areas we cover.
Our guides to extending in a conservation area, extending in the green belt and the Hampstead Garden Suburb Trust set out what each one changes.
Get your extension project completed in 3 simple steps
Tell us about your project vision and requirements through our simple online form
Our house extension specialists create detailed designs and handle all extension planning applications
We build it to a fixed, itemised price, with one project lead through to handover
What clients say
“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
One team, one fixed price, and facts you can check
North London projects are designed, managed and built by Pine Grove’s own team, so the company that draws your extension is the company on site when it is built.
Before anything is designed, we check which route your house needs: permitted development, prior approval or a full planning application.
You get a fixed, itemised figure before you sign. It only changes if you change the specification.
Our North London area guides list recent council planning decisions, approvals and refusals, each with its reference number. Start with house extensions in North London.
Rated 5.0 from 16 Google reviews. Read our Google reviews.
The Extension Company is the extensions studio of Pine Grove Design & Build Ltd, company no. 13133967, registered in England & Wales.
Design, planning and build under one fixed price — North London and across the capital
Rear, side, wrap-around and double-storey extensions, designed and built end to end.
Rear, side and wrap-around extensions, and whether yours can go ahead under permitted development.
Open-plan kitchen and family space, with the kitchen move engineered on the drawings before pricing.
The Victorian terrace classic — filling the side return to widen the ground floor.
The schemes that change what a house is, upstairs and down.
Dormer, hip-to-gable and mansard conversions — the classic winter build.
Brick piers, roof lanterns and all-year rooms, built to full building regs.
Insulated garden buildings designed around permitted development limits.
An extra room out of dead space, usually with no planning application.
Dig-outs and cellar conversions, with the structural work handled in-house.
Self-contained and multi-generational annexes, planning included.
Full renovations under one fixed, itemised price.
Planning and building-regs drawing packs, priced against what councils approve.
Where we work
Area guides built on real council planning data. Pine Grove’s own team builds across North London — start with the Enfield, Barnet and Haringey guides below.
Get answers to common home extension questions
A single-storey rear extension typically runs £60,000 to £120,000+ in North London depending on size, glazing and finish. We quote a fixed, itemised figure after a free site visit — or design yours in the Extension Builder for an honest guide price in 60 seconds.
Many single-storey extensions fall under permitted development, so no full application is needed. Where permission is required, we design to what your council demonstrably approves and handle the whole application for you.
Design and planning usually take 8-12 weeks, and a single-storey build typically 10-16 weeks on site. We agree a programme with you before work starts and manage it end to end.
The Extension Company is the extensions studio of Pine Grove Design & Build Ltd. North London projects are designed, managed and built by Pine Grove’s own team, so the company that draws your extension is the company that builds it — the job is not sold on.
Yes. You get a fixed, itemised figure before you sign, and the number you sign is the number you pay — it only changes if you change the specification.
Everything: design and drawings, the planning application, building control, structural engineering, the build itself and project management — one team from first sketch to handover.
Most London extensions touch a shared wall, so yes — we advise on party wall notices early and work alongside appointed surveyors so the agreement never holds up your build.
All our designs comply with UK building regulations, and we produce the technical drawings and manage building control sign-off as part of the fixed price.
Yes — loft conversions, wrap-arounds, double-storey extensions and whole-house transformations, in North London first and across the rest of London.
We can usually do your free site visit within days, design starts straight after, and build slots are typically booked 6-10 weeks out. Call 020 3051 9430 to check current lead times.
Have more questions? Get personalized answers below.
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Practical advice on costs, planning permission, and design from our house extension specialists.
A lawful development certificate is the council's written confirmation that your extension is legal. Here's what each type costs in 2026, how the 2024 rule change killed the 4-year rule, and how to apply properly.
Read Guide
Most extensions built "without planning permission" are perfectly lawful — that is what permitted development is. Here is what happens when a project falls outside it, and how to fix unauthorised work properly.
Read Guide
Most garden buildings are permitted development — until one of six conditions trips you up. The 2.5m boundary rule, the 50% rule and the "incidental use" test catch people constantly. How each one works.
Read GuideExplore More House Extension Services
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Speak to the team about your extension, the planning route or a rough budget. Lines open every day, 9am to 8pm.