How much does a house extension cost in the UK?
A house extension costs £2,000 to £3,200 in the UK, typically around £2,500 per m². Prices reviewed June 2026.
Extensions are priced by floor area, then by finish. A single storey extension is the common project, and the kitchen or bathroom fit-out inside it can add a lot.
Price your house extension
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House extension cost breakdown
What a house extension typically costs, by the unit:
| What | Typical UK cost |
|---|---|
| Per m², supplied and fitted | £2,000 to £3,000 per m² |
| + Fit a kitchen in the new space | add £8,000 to £20,000 |
| Typical 20 m² | £40,000 to £60,000 |
What's included in the price?
A typical house extension price includes:
- Foundations, structure, roof and shell
- Windows, doors and basic electrics
- Plastering and standard finish
- Building control
What changes the price?
The things that move a house extension price most:
Floor area in square metres and single versus double storey
Kitchen, bathroom or bi-fold doors inside the new space
Ground conditions and foundation depth
Finish level and any structural openings into the existing house
Does where you live change the cost?
London and the South East run 20 to 40 percent above the national rate per square metre.
Common questions
A typical single storey extension costs around £2,000 to £3,000 per square metre for the build, so a 20 square metre extension is roughly £40,000 to £55,000 before a kitchen fit-out.
Many single storey rear extensions are permitted development within size limits, but larger extensions, two storey work and conservation areas usually need planning permission.
These are independent guide prices based on typical UK jobs in 2026. Your actual cost depends on your property, spec, access and where you live. Always get at least three written quotes before committing.