A kitchen extension is the single most popular project in London — and the one with the widest spread of prices. Two extensions of the same size can differ by £50,000 depending on glazing, structure and the kitchen inside. Here is how the money actually breaks down in 2026, based on the extensions we price and build every month. All figures exclude VAT.
The short answer
Most single-storey kitchen extensions in London land between £70,000 and £150,000 all-in — building work, glazing, a new kitchen and fees. The build itself starts from around £2,200 per m²; the kitchen and glazing are what move the total most.
| Part of the project | Typical London range |
|---|---|
| Extension shell & finishes (per m²) | £2,200–3,500 |
| Rear glazing (sliding or Crittall-style) | £8,000–30,000 |
| Rooflights or roof lantern | £2,500–9,000 |
| New kitchen, supplied & fitted | £18,000–60,000+ |
| Underfloor heating (wet) | from £95 per m² |
| Design, structural engineer, building control, party wall | £6,000–15,000 |
A worked example
A 20 m² rear extension to a Victorian terrace, with a steel beam across the back of the house, sliding doors, two rooflights, underfloor heating and a mid-range kitchen, typically comes in around £95,000–£120,000. Taking out the side-return wall as well adds structure and party-wall work — budget a further £15,000–25,000.
What pushes the price up
- Steelwork. Opening the full width of the house needs steel beams and often posts on new foundations. The more walls you remove, the more steel.
- Glazing. Large-format sliding doors and slim steel-look frames are beautiful — and the biggest single line after the kitchen.
- Ground conditions. London clay, nearby trees and drains under the extension can all mean deeper foundations.
- Access. No side access means everything goes through the house — slower and more expensive.
- Moving the kitchen. New drainage runs and gas routes add cost; keeping the sink near the existing stack saves it.
Do you need planning permission?
Many rear extensions are possible under permitted development: a single-storey extension can go back up to 3 m from the original rear wall of a terraced or semi-detached house (4 m for detached), with a height limit of 4 m. Under the prior-approval route this can extend to 6 m (8 m detached). Wraparound and most side-return designs, and any house in a conservation area or with an Article 4 direction, usually need a full planning application. Building regulations approval is needed either way. Our planning guide explains the difference.
How long does it take?
Allow 8–12 weeks for design, approvals and party wall notices, then 12–16 weeks on site for a typical single-storey extension with a new kitchen. Kitchen lead times (often 6–10 weeks) should be ordered as soon as the layout is fixed.
How to keep the budget under control
- Finish the design — including the kitchen layout and lighting — before work starts.
- Get an itemised quote so you can see the cost of each decision.
- Keep a 10% contingency for what is found when the old walls come down.
See real examples in our Crittall-style extension and garden room extension with rooflights, or get a range for your own project in the cost calculator.
Frequently asked questions
How much does a kitchen extension cost in London?
Most single-storey kitchen extensions in London cost between £70,000 and £150,000 all-in, including the build, glazing, a new kitchen and professional fees (excluding VAT). The build itself starts from around £2,200 per m².
Do I need planning permission for a kitchen extension?
Not always. Single-storey rear extensions of up to 3 m (4 m for detached houses) can often be built under permitted development. Wraparound and side-return designs, and homes in conservation areas, usually need planning permission. Building regulations approval is always required.
How long does a kitchen extension take to build?
Typically 12–16 weeks on site, after 8–12 weeks for design, approvals and party wall notices.
Want a price for your project?
Use our calculator for an instant range, or book a free survey for a fixed, itemised quote.
