How Much Does a House Extension Cost in the UK?
An extension is usually priced per square metre of new floor area, then adjusted for the fit-out. Kitchens and bathrooms in the new space push the rate up.
Typical fitted cost per square metre. A 20m² single-storey extension is roughly £36,000–£60,000.
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Cost by extension type
What affects the price
- •Size and number of storeys — a double storey costs less per m² than two single storeys.
- •Kitchen or bathroom fit-out in the new space adds a lot on top of the shell rate.
- •Glazing — bifolds, roof lanterns and large sliding doors are premium items.
- •Groundworks and foundations, especially near drains or trees.
- •Finish level, planning and Building Regulations.
Regional price variation
Labour is the biggest regional swing. London and the South East typically run 20–30% above the national average, while the North of England, Scotland and Wales tend to sit 5–15% below it. Material prices are fairly consistent nationwide — it is day rates that move the total. The ranges on this page assume South of England pricing unless stated.
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Frequently asked questions
How much does a house extension cost in the UK?
Extensions cost around £1,800–£3,000 per square metre fitted. A typical 20m² single-storey extension is £36,000–£60,000, while a larger or higher-spec extension with a kitchen and glazing costs more.
Is a double storey extension better value?
Per square metre, yes — you reuse the same foundations and roof for two floors, so a double-storey extension usually works out cheaper per m² than a single storey, even though the total is higher.
Do I need planning permission for an extension?
Many single-storey rear extensions fall under permitted development within size limits, but larger extensions, side extensions and anything in a conservation area usually need planning permission. Building Regulations approval is always required.