Average kitchen extension costs in the UK (2026)
The build cost for a kitchen extension — foundations, walls, roof, windows, plastering and first-fix services — typically runs at £1,500–£2,800 per square metre across the UK. In the South of England and London, expect £2,000–£3,500 per m² due to higher labour costs.
| Extension size | UK build cost | South of England / London |
|---|---|---|
| 15 m² (small rear) | £22,500–£42,000 | £30,000–£52,500 |
| 20 m² (standard) | £30,000–£56,000 | £40,000–£70,000 |
| 25 m² (large open-plan) | £37,500–£70,000 | £50,000–£87,500 |
| 30 m² (wraparound / side return) | £45,000–£84,000 | £60,000–£105,000 |
These figures are for the building work only — they exclude VAT (20%), the kitchen itself, flooring, decorating, architect fees and structural engineer fees. Add all of these and the total project cost is typically 60–80% higher than the build cost alone.
Total all-in cost: what to budget
For a realistic all-in budget, a 20 m² kitchen extension in the UK typically costs:
| Cost item | Typical UK cost |
|---|---|
| Building work (20 m²) | £30,000–£56,000 |
| VAT (20%) | £6,000–£11,200 |
| Architect / designer drawings | £2,000–£6,000 |
| Structural engineer | £800–£2,000 |
| Building Regulations inspector | £600–£1,200 |
| Kitchen units, worktops & appliances | £5,000–£25,000 |
| Flooring and decoration | £2,000–£6,000 |
| Total all-in | £46,400–£107,400 |
The kitchen itself is the biggest variable. A flat-pack kitchen from IKEA or B&Q costs £2,000–£6,000 fitted. A mid-range fitted kitchen costs £8,000–£15,000. A bespoke or premium kitchen can reach £25,000–£60,000+.
Key factors that affect cost
Bi-fold or sliding doors
A set of bi-fold or sliding doors onto the garden is the defining feature of most kitchen extensions. Aluminium bi-fold doors in a standard 3–4 metre opening cost £3,500–£7,000 supplied and fitted. Larger openings or premium systems (Schuco, Origin, etc.) cost significantly more. This single item often accounts for 10–15% of the total build cost.
Roof lantern or skylight
A flat roof with a roof lantern is popular on rear extensions. A standard roof lantern costs £2,000–£5,000 supplied and fitted. A pitched glazed roof or large structural glass ceiling can add £10,000–£30,000 to the cost.
Structural steel
Opening up the wall between the extension and the existing kitchen requires a structural steel beam. Each beam typically adds £1,500–£4,000 to the job, including engineer's fees, the steel itself, and the labour to install it with temporary supports. A large open-plan rear extension with a wide span may require multiple beams.
Matching existing brickwork
If you want the extension to match the existing house brickwork — which most homeowners prefer — your bricklayer will need to source a close match. For properties built before 1990, this may mean using reclaimed bricks, which cost more. See our guide to matching brickwork.
Does a kitchen extension add value?
Yes — a kitchen-diner extension is one of the best-value home improvements you can make. Research consistently shows it adds 5–10% to a property's value, with the largest uplifts in areas where property values are high. The key is creating a genuinely useful space — a large open-plan kitchen-diner with access to the garden — rather than just adding square footage.
The uplift rarely covers the full build cost in the short term. But you benefit from the space immediately, and the value increase compounds over time with house price growth.
Do you need planning permission for a kitchen extension?
Many kitchen extensions fall within Permitted Development rights and do not need a planning application. Single-storey rear extensions up to 4 metres deep (detached houses) or 3 metres deep (semi-detached and terraced) are usually permitted development in England.
For larger extensions — up to 8 metres on a detached, 6 metres on a semi or terrace — you can use the Larger Home Extension Scheme (Prior Approval), which requires notifying the council but is not a full planning application.
See our full guide: Planning permission for a house extension.
Frequently asked questions
- How long does a kitchen extension take to build?
- The building work on a standard 20–25 m² kitchen extension typically takes 10–14 weeks once on site. Add 4–8 weeks for planning/drawings before work starts and 4–6 weeks for kitchen fitting and decoration after the build is complete. Total time from starting design to moving back in is usually 6–12 months.
- Flat roof or pitched roof — which is better for a kitchen extension?
- Both are widely used. A flat roof with a roof lantern is popular because it maximises internal height and lets in overhead light. A pitched roof matches the existing house better and may be required in some planning situations. Flat roofs cost less to build; pitched roofs cost more but can look more integrated. Ask your architect to show you both options.
- Do I need a structural engineer for a kitchen extension?
- Yes, in almost every case. You need structural calculations for the foundations, for any steel beams spanning openings in the existing wall, and for the roof structure. The structural engineer produces these drawings for Building Regulations. Budget £800–£2,000.
- Can I live in the house during a kitchen extension build?
- Usually yes, though it is disruptive. The main difficulty is when the existing kitchen wall is opened up to join the two spaces — you will be without a usable kitchen for several weeks at that point. Many families use a temporary kitchen (microwave, kettle, mini-fridge) in another room. If you have young children or work from home, it is worth planning for this disruption in advance.