Adding space to your home is one of the biggest decisions a family makes, and it should feel exciting rather than stressful. At Kev Construct we build extensions across Edgware, Barnet, Enfield, Harrow and the wider North London area, and clear pricing is part of how we work. Marian handles our quotes personally, so you get an honest breakdown with no hidden fees.
How much does a single-storey extension cost?
A single-storey rear extension is the most popular way to gain a bigger kitchen or a light-filled family room. As a 2026 North London guide, expect £50,000-£90,000 for a good-quality build. A side-return extension, which fills in the awkward alley beside many Victorian and Edwardian homes, sits at £55,000-£95,000.
Where you land in that range depends on the footprint, the amount of glazing, and whether you want premium items such as bi-fold doors, underfloor heating or a large roof lantern. Kitchens and bathrooms also add cost, because plumbing, tiling and units are priced on top of the shell.
How much does a double-storey extension cost?
A double-storey extension gives you two rooms for not much more groundwork than one, which is why many families see it as strong value. As a 2026 North London guide, expect £70,000-£130,000. You are effectively adding a downstairs room plus an extra bedroom or bathroom above, so it is a bigger project with a longer programme.
Because a double-storey build changes the look of your home and can affect neighbours, it almost always needs planning permission, and the Party Wall Act often applies. We cover those steps below.
What does an extension quote include?
Here is a simple guide to typical types, prices and timescales. These are 2026 North London guide prices only, and every home is different.
A full quote from us usually covers groundworks and foundations, the structural shell, roofing, windows and doors, plastering, first and second fix, and making good. Kitchens, bathrooms and high-end finishes are listed separately so you can see exactly what you are paying for.
What else affects the final price?
A few things move the number up or down:
- Ground conditions, such as clay soil, trees or old drains, which can mean deeper foundations
- Access to the rear of the property, since a tight side passage slows deliveries
- The specification of kitchens, bathrooms, flooring and glazing
- Structural work like steel beams to open up the ground floor
- Professional fees for drawings, structural calculations and building control
How long does a single-storey extension take?
Most single-storey rear extensions take around 8-12 weeks on site once work begins, weather and materials permitting. Double-storey projects usually run longer at 12-18 weeks. John runs our sites day to day, with Dan and Niko on the build, so you always know who is on your project and what happens next.
We are proud of our Checkatrade rating of 9.67/10 from verified reviews, and careful planning is a big part of keeping a job on track.
Frequently asked questions
How much does a house extension cost in North London?
As a 2026 guide, a single-storey extension costs £50,000-£90,000 and a double-storey extension costs £70,000-£130,000. Size, finishes and ground conditions all affect the final price.
Is a double-storey extension better value than single-storey?
Often yes, because you gain two rooms for roughly one set of foundations and one roof. It costs more overall but can work out cheaper per square metre.
Do your estimates cost anything?
No. We provide free estimates with a clear, itemised breakdown, so you can plan your budget before committing to anything.
Ready to talk numbers for your home? Browse our full house extensions service and request a free, no-obligation estimate today.
