Cost guide
How much does a house extension cost?
The published UK per-m² rate for a single-storey extension, and what actually moves it.
A single-storey house extension in the UK typically costs £1,800–£3,000 per m², according to HomeOwners Alliance and Checkatrade — so a 20m² extension runs roughly £40,000–£56,000, a 30m² extension £60,000–£84,000, and a 50m² extension £100,000–£140,000. These figures exclude VAT and are general UK averages, not a quote for your project.
Last updated 17 August 2026
| Range | ||
|---|---|---|
| General rate | £1,800–£3,000 | Per m² |
| 20m² extension | £40,000–£56,000 | Total project |
| 30m² extension | £60,000–£84,000 | Total project |
| 50m² extension | £100,000–£140,000 | Total project |
Sources: HomeOwners Alliance (2026 guide), Checkatrade (updated June 2026, figures exclude VAT), Federation of Master Builders (UK average, no date shown on source page)
Key points
- Roof design — a simple flat roof generally costs less than a more complex roofline.
- The number of structural openings, and glazing specification.
- Ground conditions, drainage and site access.
- Whether services (electrics, plumbing) need extending into the new space.
- Region — costs run higher in London and the South East than the UK average quoted here.
These are general published ranges, not a quote. Get an estimate based on your own project.
Start Your ProjectWant to understand what drives this cost, not just the numbers? Read how much does an extension cost? →
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Other cost guides
More published cost ranges
How much does a loft conversion cost?
Published industry ranges by conversion type, so you can budget sensibly before getting a quote.
How much does a two storey extension cost?
Published per-m² rates by build quality, and what a typical two-storey extension runs in total.
How much does a side extension cost?
Published UK ranges for a side and side-return extension.
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