How Much Does a Kitchen Extension Cost in 2026? (UK)
A kitchen extension in the UK costs £35,000 to £75,000 in 2026, covering the extension shell and the kitchen fit-out. It's the UK's most popular home improvement — and adds significant value. Here's the full 2026 cost breakdown.
Kitchen extension cost at a glance
A typical kitchen extension in the UK in 2026 costs £35,000–£75,000 — broken down as roughly £1,800–£2,500/m² for the build and £8,000–£30,000 for the kitchen itself.
- Small kitchen extension (15m²): £35,000 – £50,000
- Medium kitchen extension (25m²): £50,000 – £75,000
- Large kitchen-diner extension (40m²): £75,000 – £110,000
- Side return extension (London terraces): £45,000 – £70,000
London and the South East typically add 20–25%. A kitchen extension adds 10–18% to UK property value — often more than the build cost on properties above £400,000.
The single biggest mistake we see in kitchen-extension quotes
When homeowners approach us about kitchen extensions, around 70% quote a single number they've found online — "I've budgeted £45,000 for a kitchen extension" — and they're usually out by 30–40%. Not because they've been misled, but because the figure they've found is for the extension shell only, not the kitchen inside it. These are two completely separate projects with separate cost structures, and it's the single most expensive misunderstanding we see. Whether an extension is the right move at all — versus going up into the roof — is worth pressure-testing first: our loft conversion versus extension comparison weighs the value each adds, and if a faster build appeals, our steel-frame extension analysis shows where modern methods do and don't save money.
A typical 25m² rear kitchen extension in 2026 breaks down like this: the extension shell (foundations, walls, roof, structural openings, Building Control) is £40,000–£55,000; the kitchen fit-out (units, worktops, appliances, sink, tap, lighting, installation labour) adds £12,000–£35,000 depending on spec; knocking through to join the new space to the existing kitchen adds £2,500–£4,500 in RSJ steels and plaster-work; flooring across the joined space adds £2,000–£5,000. The all-in figure is rarely below £58,000 even for a budget scheme, and hits £95,000+ for a high-specification kitchen-diner with bifolds, a lantern roof and a decent appliance package.
The fix: when you ask builders for a quote, be explicit about what's included. Ask for "extension shell + kitchen fit-out combined" or "extension shell only — kitchen priced separately" and compare like with like. The worst budget blow-ups we see are homeowners who agree a £48,000 shell-only quote, realise three months in that the kitchen itself is another £20,000+, and can't stop the build. Plan the full number from day one.
2026 Kitchen Extension — Shell + Fit-Out Split
A kitchen extension has two parts: the extension itself (shell) and the kitchen (fit-out). Most homeowners underestimate the fit-out cost. Here's a realistic 2026 split.
| Element | Budget Spec | Mid-Range | High-End |
|---|---|---|---|
| Extension shell (20m²) | £36,000 | £45,000 | £55,000 |
| Kitchen units & worktops | £5,000 | £12,000 | £25,000 |
| Appliances | £1,800 | £4,500 | £10,000 |
| Flooring (LVT / tile / engineered wood) | £1,200 | £2,400 | £4,800 |
| Bifold / sliding doors | £3,500 | £6,500 | £12,000 |
| Lantern / skylights | £0 | £2,500 | £6,000 |
| Underfloor heating | £0 | £1,800 | £3,500 |
| Total (20m² kitchen extension) | £47,500 | £74,700 | £116,300 |
Prices include all labour, materials, building control and VAT. Add 10% contingency. Regional variation: +25% London, −10% to −15% North England, Wales and Scotland.
Kitchen Extension Types & 2026 Prices
Most popular — full kitchen-diner
Build onto the back of the house to create an open-plan kitchen-dining space. Usually under Permitted Development. The gold standard for UK family homes.
London terrace classic
Extends into the unused side passage. Transforms dark Victorian kitchens into bright, wide open-plan spaces. Typical 5–6m² uplift.
Maximum kitchen space
Rear + side combined. Creates the largest open-plan kitchen-living space possible on a single floor. Planning usually required.
Classic family extension
Generic single-storey rear extension used for a new kitchen. Flat roof or pitched, with glazing to the garden.
Kitchen + bedroom above
Kitchen-diner downstairs plus an extra bedroom or ensuite above. Best value per m² — shares foundations and roof with existing house.
Lower-cost alternative
Solid-roof orangery or conservatory extension. Usable year-round with underfloor heating. Limits kitchen layout flexibility.
How to Save £5,000–£15,000 on a Kitchen Extension in 2026
Kitchen extensions are where budgets most often slip. Here are six specific moves that save UK homeowners thousands in 2026 without compromising the finished result:
- Get 3 quotes, not 1. Prices vary 20–30% between builders for identical specs — a £60,000 job can come in at £48,000 from a different quote. Free to do, saves thousands.
- Stay within Permitted Development. Avoid a £258 planning fee plus £2,000–£4,000 of architect resubmissions. PD also saves 8–12 weeks of project time.
- Choose flat roof over pitched. A GRP or EPDM flat roof is £3,000–£6,000 cheaper than a pitched roof for the same footprint — and modern finishes look sharp.
- Skip the roof lantern. Lanterns add £3,000–£6,000. Two well-placed Velux rooflights give similar daylighting at a third of the cost.
- Supply your own kitchen. Buying units direct from Howdens/Wren/Magnet and asking your builder to install can save £3,000–£8,000 vs a turnkey kitchen specialist.
- Time the build for spring. January–March is builder low season — expect 5–10% lower quotes. Avoid October–December when everyone wants work done before Christmas.
More Kitchen & Extension Guides
All cost guides →Rear Extension Cost 2026
Full guide to rear extension costs by size with regional data.
Loft Conversion Cost 2026
Loft conversion costs by type — Velux, dormer, hip-to-gable, mansard.
Kitchen Renovation Cost
Costs for a new kitchen without extending — units, worktops, fit.
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Kitchen Extension Cost FAQs
Our sources for this guide
Every figure in this guide is cross-referenced against primary UK sources. We cite the specific documents and data providers we used so you can verify and dig deeper.
- KBSA — Kitchen Bathroom Bedroom Specialists Association
- Federation of Master Builders — extension guide
- gov.uk — Approved Document Part L
- Planning Portal — extension planning
- RICS BCIS — UK construction costs
- NICEIC — certified electricians
Links open in a new tab on external sites. We do not benefit commercially from any of these links; they are included to help readers verify claims and research further. If you spot a broken or outdated link, email info@bestbuilders.co.uk.
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Kitchen extension — guides and detail
The detail behind the number: what changes the price, the planning position, and how to check a quote before you accept it.
Written by the BestBuilders Editorial Team. Based on BestBuilders’ 2026 regional cost model (national cost guides × regional labour index), industry research and primary UK source material. Last updated: 23 August 2026.