How Much Does a House Extension Cost in 2026?
An extension adds space and value without the cost of moving. Price depends on size, number of storeys, finish and your location.
Cost breakdown
| Single storey extension (per m²) | £1,500–£2,500 |
| Double storey extension (per m²) | £1,800–£2,800 |
| Typical single storey (20m²) | £30,000–£50,000 |
| Kitchen extension with fit-out | £40,000–£70,000 |
| London premium | +20–40% |
What affects the price
- •Size and number of storeys
- •Groundwork and foundations
- •Glazing, roofing and finish
- •Kitchen or bathroom fit-out
- •Planning and building control
FAQs
How much does a single storey extension cost?
Typically £1,500–£2,500 per square metre in the UK, more in London. A 20m² extension is usually £30,000–£50,000.
Do I need planning permission for an extension?
Many extensions fall under permitted development, but larger ones need planning permission. Building regulations always apply.
How long does an extension take to build?
A single storey extension typically takes 3–4 months from groundwork to finish.
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