House extension cost in North London
As a guide for North London in 2026, a single-storey extension costs around £50,000-£90,000, a side return around £55,000-£95,000, and a double-storey around £70,000-£130,000. These are guide ranges, not fixed prices. Your final cost depends on size, specification and site conditions, and every quote we give is fixed and fully itemised.
A look at recent extensions
What does a house extension cost by type?
As a guide for North London in 2026, a single-storey extension costs around £50,000-£90,000, a side return around £55,000-£95,000, and a double-storey around £70,000-£130,000. These are guide ranges, not fixed prices, and every quote we give is fixed and fully itemised, with no hidden fees.
Different extensions add space in different ways, so the price varies with the type of build. Use the guide ranges below as a starting point, then talk to us for a fixed price based on your actual house and plans.
Guide ranges for North London, 2026 - not fixed quotes. We quote every project individually and put the final figure in writing before any work begins. A double-storey build often works out at a lower cost per square metre than doing two separate projects, because you build both floors together.
What affects the cost of an extension?
The size of the extension is only the starting point. The finishes you choose, the amount of glazing, and the ground you are building on all make a real difference to the final figure. Understanding these factors early helps you set a realistic budget and avoid disappointment later.
- Size and shape. A larger footprint costs more, but the price per square metre often falls as the extension grows, because fixed costs are spread further.
- Specification and finishes. Kitchens, bathrooms, flooring, glazing and joinery can vary hugely in price. A high-end kitchen or large sliding doors will push the figure up.
- Structural work. Steel beams, underpinning and removing load-bearing walls add cost, especially on open-plan layouts.
- Ground and site conditions. Difficult access, drainage that needs moving, or poor ground that needs deeper foundations all affect the price.
- Roofing and glazing. Flat roofs, pitched roofs, roof lanterns and skylights each carry different costs.
What is not included in the build price?
A build price usually covers the structure and finishes we agree, but some costs sit outside it, and we will always flag these so you can budget for the whole project, not just the building work.
- Architect and structural engineer drawings.
- Planning application fees, where planning permission is needed.
- Building regulations and building control fees.
- Party Wall Act surveyor fees, if a neighbour requires one.
We will point you to trusted people for drawings and paperwork where you need them, and we work alongside your architect if you already have one. Our planning permission guide explains which of these apply to your project.
A fixed, itemised price in writing
We visit your home, measure up, talk through what you want, and then Marian prepares a fixed, written quote with everything itemised. You will see exactly what is included, line by line, so you can compare fairly and know the price will not creep up once we start. Free estimates, no hidden fees, no pressure.
We are a proper limited company, Kev Construct Ltd, Company No. 12080875, and our work is backed by the £1,000 Checkatrade Guarantee.
What our customers say.
“John and the whole crew were a pleasure to work with. Fast, great communication, finished on time and to a high quality.”
“Dan and Niko put real care into the work; Marian set everything out clearly with no hidden fees. They went above and beyond.”
“We're an architecture practice and have worked with Kev Construct for years. Reliable, trustworthy, excellent finishes.”
Good to know.
Why are these prices given as guides and not fixed?
Because no two homes are the same. Ground conditions, access, the finishes you choose and any structural work all move the figure up or down. Published ranges help you budget, but the only accurate number is a quote based on your actual house and plans. Marian will give you a fixed, fully itemised written price after a free visit, with no hidden fees.
How do payments work during the build?
We agree a clear payment schedule in writing before we start, usually in stages that match progress on site, so you never pay far ahead of the work done. There is no large upfront deposit for the sake of it. You will always know what the next payment is for and when it falls due, because it is set out in your quote from the start.
Can I reduce the cost without cutting corners?
Yes. Often the biggest savings come from the specification rather than the structure. Choosing a mid-range kitchen, standard doors instead of large bespoke glazing, or a simpler roof design can bring the figure down while keeping the build quality high. We are happy to price a couple of options so you can see the difference and decide what matters most to you.
Will the price change once work starts?
Our fixed quote is the price you pay, provided the job stays as agreed. The only time the figure changes is if you ask for extra work, or if something genuinely unforeseen appears once we open up, such as hidden ground problems. If that happens, we stop, explain it clearly and agree any change in writing before we carry on. No surprises.
Want a real price
for your extension?
Tell us about your project and we'll arrange a free home visit. You'll get a clear, fixed price in writing - with everything itemised and no hidden fees.
- Free home visit & survey
- Fixed price in writing - no surprises
Prefer to talk? 07838 662 225