Extensions built around how you actually live
Rear, side return, double storey and wraparound extensions that add the space and light your home is missing.
You love where you live, but the house has run out of room. Moving means stamp duty, upheaval and leaving the area you chose. The right extension gives you the space without any of that, and an extension is usually about one thing: the kitchen and living space a modern family actually lives in.
We build extensions that feel part of the original house rather than bolted on, with the glazing, flooring and flow thought through from the first drawing. We can take the project from bare plans to completion, or work alongside your architect and designer.
Firtree Build designs and builds house extensions across North London, Enfield and Hertfordshire. Whether you want a bright rear extension for an open plan kitchen, a side return to widen a terrace, or a double storey extension to add bedrooms above and living space below, we manage the whole project from design and planning to a finished, decorated room.
Find the right extension for your home.
Rear extensions
Extending into the garden to create an open plan kitchen, dining and living space full of natural light. Ideal where the back of the house feels dark or cut off from the garden. Many fall under permitted development, which we check before design starts. Typically 8 to 12 weeks on site.
Side return extensions
Turning the narrow alley beside a Victorian or Edwardian terrace into usable space, widening the whole ground floor. One of the best ways to get a proper kitchen diner without losing much garden. Roof lights keep it bright, and we handle the party wall process with your neighbours.
Double storey extensions
More space on two floors in one project: a bigger kitchen or living area downstairs and an extra bedroom or bathroom above. Usually better value than two separate builds, as the foundations, scaffolding and roof are done once. Typically 12 to 16 weeks on site, and usually needs full planning, which we help you through.
Wraparound extensions
A rear and side return extension combined into one L shaped space that transforms the whole ground floor. Suits families who want one large open plan room for cooking, eating and relaxing, with space for a utility or WC. Typically 14 to 20 weeks on site.
Kitchen extensions
An extension designed around the kitchen from day one, with the layout, lighting, glazing and doors planned together. We work with you or your kitchen supplier so the services, steels and openings are in place before the kitchen goes in.
how it works
Consultation, quote, then a well managed build.
01
Consultation
We visit, listen, and advise on the best option for your home and budget.
02
Quote & design
An itemised quote and a design, with planning handled where needed.
03
Managed build
A well managed build, start to finish, with regular updates.
“A lighter, larger home that works for your family and adds real value, finished by a team you could actually trust.”
See the work
FREQUENTLY ASKED QUESTIONS
Good to know before you get in touch
How long does a house extension take to build in North London?
A single storey rear extension typically takes 8 to 12 weeks on site, a double storey 12 to 16 weeks, and a wraparound 14 to 20 weeks. Before the build you also need to allow around 8 to 15 weeks for design, structural drawings and building control if the work is permitted development, or 16 to 26 weeks if it needs a full planning application. So a standard single storey extension in Enfield or North London usually runs about 6 to 9 months from first drawing to finished room. Firtree gives you a fixed build programme once the drawings are signed off.
How much value does an extension add to a property in North London?
A single storey rear extension typically adds 5 to 10% to the value of a North London home, an open plan kitchen or wraparound extension 10 to 15%, and a double storey extension 15 to 20%. On a £600,000 Enfield property that is roughly £30,000 to £120,000 depending on the type. Returns are strongest in higher demand areas like Barnet, Finchley and Winchmore Hill. The uplift depends on the quality of finish and how much the new space improves the layout, not just the extra floor area.
How much does a house extension cost in North London?
As a 2026 guide, single storey extensions in London run about £2,500 to £4,500 per square metre. So a typical 20m² rear extension lands around £55,000 to £85,000 all in, and a 30m² around £80,000 to £120,000. A wraparound of 35 to 50m² is usually £100,000 to £160,000. Design and structural fees add roughly £6,500 to £15,000, and the kitchen itself is priced separately on top. Firtree quotes a detailed fixed price on the agreed drawings, so you are not exposed to an open ended day rate that creeps up as the job runs.
Do I need planning permission for an extension in North London?
Many single storey rear extensions do not need planning permission because they fall under permitted development: up to 3 metres deep on a terraced or semi detached house, 4 metres on a detached house, and no more than 4 metres high. You can sometimes extend to 6 or 8 metres under the Larger Home Extension prior approval route. You will need full householder planning permission if you are in a conservation area, if an Article 4 direction applies, or if the property is listed. These are all common across parts of Enfield, Haringey and Barnet. Building regulations approval is required either way.
How do I know if my house can be extended?
Almost every house in North London can take some form of extension, but what is realistic depends on your plot size, where the drains and boundaries sit, the existing foundations, and whether you are in a conservation area. Semi detached and end of terrace homes across Enfield and Southgate usually have side or rear space to work with; mid terrace homes tend to suit rear or side return extensions. Firtree runs a free feasibility check and tells you what will and will not get approved before you spend money on drawings.
Why do extensions go over budget, and how do you stop that?
Extensions overrun for three main reasons: vague quotes that leave items out, structural surprises found once work starts, and design changes partway through the build. Firtree prices to a detailed fixed quote, flags structural risks like underpinning or steel beams up front in the survey, and locks the specification before starting. The number you agree is the number you pay, barring changes you choose to make.
Will I need a party wall agreement?
If your extension is built on or near the boundary with a neighbour, or its foundations are dug within 3 to 6 metres of their property, you will need to serve a party wall notice. That is at least one month before work starts for a new wall on the boundary or nearby excavation, and two months for work to an existing party wall. If your neighbour agrees in writing, no surveyor is needed; if not, a party wall surveyor is appointed, typically from around £1,000 per neighbour.
Can I stay in the house during an extension?
In most cases, yes. A rear or side extension is built off the back of the house with the existing wall kept in place until late in the programme, so day to day disruption is limited. The most disruptive phase is the break through, when the new space is opened up to the house, which usually lasts a few days. Firtree schedules that phase with you in advance so you can plan around it.
Ready when you are
Ready to talk about
your extension?
Tell us what you have in mind and we will come back with honest advice and a clear quote.