Kitchen Extension Cost UK 2026: build, kitchen FF&E and the PC sum trap
What a kitchen extension actually costs in 2026, with the kitchen specification ranges that move the bill and the PC-sum trap most builders use.
Key facts
- Build cost: £2,400–£3,400/m² UK, £3,200–£4,400/m² London for a single-storey kitchen extension.
- Trade-spec kitchen + appliances: £12,000–£25,000.
- Mid-range kitchen with integrated appliances: £25,000–£50,000.
- Designer / handmade kitchen: £60,000–£150,000+.
- Glazing (sliders, Crittall, structural glass) swings the build cost by £15,000–£30,000.
- Professional fees and VAT add 25–30% on top of the build cost.
A kitchen extension is the single most popular residential project type in the UK. It is also one of the easiest to overspend on, because two distinct budgets (build cost and kitchen) are usually merged into one number that satisfies neither. This guide separates them properly and walks through the 2026 ranges.
A kitchen extension is two projects in one trench: the build and the kitchen. Price them separately. Quote them separately. Manage them separately.
Kitchen extension cost by part, 2026
Build cost (the extension itself)
£2,400–£3,400/m² outside London. £3,200–£4,400/m² in Greater London. Single-storey rear or side-return extension, including foundations, structure, roof, glazing, plaster, flooring substrate, MEP first-fix and the structural opening into the existing kitchen. Same rates as a non-kitchen extension; see house extension cost UK 2026 for the full breakdown by type.
The kitchen itself
Three working tiers, prices include cabinets, worktops, appliances, tiling and lighting:
- Trade-spec: £12,000–£25,000. Howdens, Wickes, Magnet trade range, mid-range integrated appliances.
- Mid-range: £25,000–£50,000. DeVOL, Wren, mid-tier independents, Bosch / Neff / Miele appliances, stone or sintered worktops.
- Designer / handmade: £60,000–£150,000+. Plain English, Roundhouse, Pluck, Smallbone, full Gaggenau or Sub-Zero appliance package.
A £40,000 mid-range kitchen with integrated appliances and stone worktops is the typical London spec on a £100,000 extension.
The Prime Cost (PC) sum trap
Most builder quotes include a Prime Cost sum for the kitchen, often £15,000–£20,000, used as a placeholder before the homeowner chooses the actual kitchen. The trap:
- Builder uses a low PC to win the quote.
- Homeowner picks a real kitchen at £40,000.
- Builder bills the £20,000 difference as a variation, plus 15–25% OHP on the variation.
- Homeowner pays £5,000 more in mark-up than if they had pinned the kitchen down before quote.
Fix: get a real kitchen quote first, fix the kitchen scope in the pricing document, and pay the builder only a fitting allowance. Buy the kitchen yourself.
What moves the build-cost price inside the range
- Glazing. Standard aluminium sliders: £8,000–£12,000. Crittall: £15,000–£25,000. Structural glass: £25,000+. The single biggest swing factor.
- Structural opening. Removing a load-bearing wall between existing kitchen and new extension adds £8,000–£15,000.
- Underfloor heating. Adds £80–£120/m² of floor.
- Rooflight specification. Standard flat rooflight: £1,500–£3,000. Walk-on or structural glass rooflight: £6,000–£15,000.
- Foundations. Trees within 10m of the extension trigger deeper foundations, +£3,000–£10,000.
What the headline price excludes
| Item | Typical 2026 cost (London 25m² kitchen extension) | | --- | --- | | Build (25m² × £3,800/m²) | £95,000 | | Mid-range kitchen + appliances | £35,000 | | Architect (design 1–5) | £10,000–£16,000 | | Structural engineer | £2,000–£4,500 | | Party wall (per neighbour) | £1,500–£3,500 | | Building control | £900–£1,500 | | Independent cost expert | £3,000–£7,000 | | Off-site living (8–10 weeks) | £4,000–£10,000 | | VAT (20% on construction + kitchen) | £26,000+ | | Typical total | £180,000–£210,000 |
Contingency
10–15% on extensions to older properties. 7–10% on clean new extensions on a solid existing slab. Anything below 7% is optimistic.
Common kitchen extension cost mistakes
- Accepting a builder's PC sum without pinning the kitchen down.
- Buying the kitchen through the builder. Pays a 10–25% mark-up for no benefit.
- Building during summer with the family at home. Programme stretches; prelims rise.
- No allowance for snagging the kitchen separately from the build.
Should you appoint a cost expert?
For kitchen extensions under £80,000, a cost-checked schedule of works usually covers it. Above £150,000, an independent cost expert pays for itself. Our extension and refurbishment costing service and builder quote audit cover the kitchen-extension use case.
Related reading
- House extension cost UK 2026, the full breakdown by extension type.
- Side return extension cost London, the typical London kitchen extension.
- Why most building quotes are wrong, the PC-sum mechanics in detail.
Get a fixed-fee proposal for your kitchen extension via our fee proposal form. We reply within one UK working day.
Frequently asked
- How much does a kitchen extension cost in 2026?
- Outside London, a 25m² single-storey kitchen extension costs £60,000–£85,000 in build cost plus £25,000–£40,000 for a mid-range kitchen. Inside Greater London, the same extension is £80,000–£110,000 in build cost plus a similar kitchen budget. Add 25–30% on top for fees, party wall and VAT to reach total project cost.
- What is a PC sum and why is it a trap?
- A Prime Cost sum is a placeholder figure the builder inserts in a quote when the actual item has not been chosen yet, typically kitchens, bathrooms, joinery and lighting. The trap: builders insert a low PC sum to win the job, then bill the difference once the homeowner picks the real product. Always pin the kitchen down before quote.
- Should I buy the kitchen myself or through the builder?
- Buy it yourself. You avoid the contractor's 10–25% mark-up, you keep direct control of specification and substitution, and you control the supplier relationship for snagging. Pay the builder a fitting allowance only.
- How much does the glazing cost?
- Standard aluminium sliders to a 4m opening: £8,000–£12,000. Crittall or steel-framed bifolds: £15,000–£25,000. Frameless structural glass corner or sliding doors: £25,000–£60,000. Glazing is the single biggest swing factor in a kitchen extension budget.
- Do I need planning permission for a kitchen extension?
- Most single-storey rear extensions in England fall under Permitted Development (up to 6m on detached, 4m on semi/terraced, lower in conservation areas). Side-return kitchen extensions on Victorian terraces are usually PD up to the side boundary. Always confirm with your local authority before quote.
- Should I move the kitchen during the build?
- Yes. Almost always. Living through a kitchen extension with no functional kitchen extends programme by 4–8 weeks, lifts prelims, and is the single biggest source of homeowner dispute we are asked to mediate. Budget for a temporary kitchen elsewhere in the house or a rental.
- Do I need a cost expert for a kitchen extension?
- For kitchen extensions under £80,000, a cost-checked schedule of works is usually enough. Above £150,000, an [independent cost expert](/homeowners/insights/what-does-a-quantity-surveyor-do) almost always saves multiples of the fee. Our [extension and refurbishment costing service](/homeowners/services/extension-costing) is built around this use case.
- Is VAT charged on a kitchen extension?
- Yes, at 20% in almost all cases, because the work is on an existing home. See our [VAT on home building work](/homeowners/insights/vat-on-home-building-work) guide for the narrow exceptions.
