How much is a single storey extension?

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.

Do I need planning permission for an extension?

Many single storey rear extensions are permitted development within size limits, but larger extensions, two storey work and conservation areas usually need planning permission.

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How much does a house extension cost in the UK?

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.

From

£2,000

Typical

£2,500

Up to

£3,200

per m² · typical UK job, 2026

Time on site: 10 to 16 weeks for a single storey extension

Price your house extension

Adjust for your job and area to get a range.

What's included in the price

Foundations, structure, roof and shell
Windows, doors and basic electrics
Plastering and standard finish
Building control

What changes the cost

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

Costs by area

London and the South East run 20 to 40 percent above the national rate per square metre.

Common questions

How much is a single storey extension?: 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.
Do I need planning permission for an extension?: 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.