A kitchen extension is one of the most popular home improvements in the UK - and one of the most expensive. Getting the price wrong at the quoting stage causes problems for everyone: the homeowner gets a nasty surprise, and the builder ends up working for less than they should.
Whether you're a homeowner trying to budget or a builder trying to price accurately, this guide covers the real costs of kitchen extensions in the UK in 2026.
The short answer: a kitchen extension in the UK typically costs between £1,500 and £2,800 per square metre for the building work alone. A standard 4m x 5m single-storey rear extension comes in at £30,000 to £56,000 depending on your location and specification.
But that's just the structure. Once you add the kitchen itself, electrics, plumbing, flooring, decoration, and professional fees, the all-in cost for a finished kitchen extension is more realistically £50,000 to £100,000.
These numbers vary enormously by region. A kitchen extension in central London can cost double what the same build costs in the Midlands or North East.
This is the classic kitchen extension - knocking out the back wall and extending into the garden. Typically 3m to 6m deep across the full width of the house.
Building work only: £30,000-£65,000 for a 15-25m² extension.
With kitchen and finishing: £50,000-£95,000.
Typical build time: 10-16 weeks.
This is usually the most cost-effective option because the structure is simple, the roof is straightforward (flat or lean-to), and it can often be done under Permitted Development without a full planning application.
Common on Victorian and Edwardian terraced houses where there's a narrow alley (side return) running alongside the kitchen. You extend into this dead space to create a wider kitchen.
Building work only: £25,000-£50,000 (typically smaller area, 8-15m²).
With kitchen and finishing: £40,000-£75,000.
Typical build time: 8-12 weeks.
Side returns are popular because they make a dramatic difference to the kitchen width without eating into much garden space. However, they often require a steel beam to support the existing wall above, which adds structural cost.
A combination of rear and side extensions that wraps around the corner of the house. Creates the largest possible kitchen-diner space.
Building work only: £45,000-£90,000 (20-35m²).
With kitchen and finishing: £70,000-£140,000.
Typical build time: 14-20 weeks.
More expensive because it involves two external walls, more steelwork, and a more complex roof junction. But the result is usually a spectacular open-plan kitchen-diner-living space.
A complete kitchen extension price should cover all of these elements. If a quote misses any of them, the "extras" will appear later.
Groundworks and foundations: Excavation, concrete foundations, damp proof course, drainage connections. This alone can be £5,000-£12,000 depending on ground conditions. If you hit clay, rock, or need deeper foundations near trees, costs increase.
Structural work: Walls (block, brick, or timber frame), steelwork (RSJs to open up the existing wall), roof structure, windows and doors including bi-fold or sliding doors. The bi-folds alone can be £3,000-£8,000.
Roof: Flat roof (EPDM or fibreglass) or pitched roof with tiles. Flat roofs are cheaper at £2,000-£5,000. Pitched roofs add £5,000-£12,000 but look better and last longer.
First fix: Plumbing rough-in, electrical wiring, plastering, insulation. Insulation must meet current Building Regulations - Part L requirements mean you'll likely need 100mm+ of rigid insulation in the floor and roof.
Kitchen: Units, worktops, appliances, splashback, sink, taps. Budget £5,000-£8,000 for a decent mid-range kitchen from Howdens or Wren. Premium kitchens from bespoke joiners start at £15,000.
Second fix and finishing: Electrics (sockets, switches, lighting), plumbing connections, flooring, decoration, skirting, door furniture. Underfloor heating is popular in kitchen extensions and adds £1,500-£3,000.
Professional fees: Architect (£2,000-£5,000), structural engineer (£500-£1,500), Building Control application (£500-£1,000), planning application if needed (£206 for householder in England). Party wall surveyor if you're building on or near the boundary (£700-£1,500 per neighbour).
Location has a massive impact on extension costs. Labour rates, material delivery costs, and competition all vary by region.
London: £2,200-£3,500 per m². The most expensive market in the UK by a wide margin.
South East (outside London): £1,800-£2,800 per m². Reading, Brighton, Oxford, and surrounding areas.
South West: £1,500-£2,400 per m². Bristol, Bath, Exeter.
Midlands: £1,400-£2,200 per m². Birmingham, Nottingham, Leicester.
North West: £1,300-£2,100 per m². Manchester, Liverpool, Chester.
North East: £1,200-£2,000 per m². Newcastle, Sunderland, Durham.
Scotland: £1,300-£2,200 per m². Edinburgh at the higher end, elsewhere lower.
Wales: £1,200-£2,000 per m². Cardiff higher, rural areas lower.
If you're a builder pricing a kitchen extension, accuracy matters more here than on any other job. Underquoting on a £50K project doesn't just cost you a few hundred quid - it can cost you thousands.
Measure everything. Don't estimate from photos or verbal descriptions. Visit the site, measure the footprint, check the existing structure, look at ground conditions, and note any complications (drainage runs, trees near foundations, sloping ground, access issues).
Get structural engineer input early. Don't guess at steel sizes or foundation depths. A structural engineer's preliminary advice (often free or cheap) helps you price accurately and avoids nasty surprises mid-build.
Price every trade separately. Break your quote into groundworks, structural, roof, first fix, second fix, and finishing. This makes it easier to check your numbers and easier for the customer to understand.
Add contingency. On extension work, 10-15% contingency is sensible. Old houses throw up surprises - rotten joists, unexpected drainage, asbestos, boundary disputes. Build this into your price or state it as a separate line item.
Present a professional quote. A kitchen extension is a major purchase for the homeowner. They're comparing you against other builders, and the quality of your quote signals the quality of your work. A clear, itemised, professionally formatted quote wins over a scribbled number on the back of a business card every time.
If you want to produce professional PDF proposals quickly, QuoteSmith lets you create polished quotes in minutes. Type the job details, adjust the pricing, and send a branded proposal that makes you look like an established company.
Many single-storey rear extensions fall under Permitted Development (PD) rights, meaning no planning application is needed. However, PD has limits: maximum 3m projection for semi-detached/terraced houses or 4m for detached, maximum 4m height, and you can't cover more than 50% of the garden. If you're in a conservation area or your home is listed, you'll almost certainly need planning permission. Always check with your local planning authority before starting.
A straightforward single-storey rear extension takes 10-16 weeks from breaking ground to handover. More complex builds (wrap-around, structural complications, premium finishes) can take 16-24 weeks. Add 4-8 weeks before building starts for design, planning, and Building Regulations approval.
Generally yes. A well-designed kitchen extension typically adds 5-15% to property value, and in some areas the return exceeds the cost of the build. The key is making it feel like part of the original house, not a bolted-on afterthought. Open-plan kitchen-diners with good natural light add the most value.
You can save 10-15% by managing trades yourself, but it's a significant time commitment and requires knowledge of the build sequence, Building Regulations, and how to coordinate multiple tradespeople. Most homeowners are better off paying a builder or project manager to handle it, especially if they're working full-time.
A side return extension (if your house has one) is usually the cheapest option because the area is smaller. A lean-to with a flat roof is cheaper than a pitched roof. Using a timber frame system instead of traditional block is faster and can reduce labour costs. And keeping the existing plumbing and drainage positions where possible avoids expensive underground work.
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