Cost guide
What's the cost per square metre for an extension?
The per-m² method explained, and the published UK rate.
UK extensions are typically priced at £1,800–£3,000 per m², according to HomeOwners Alliance and Checkatrade, though this is a general guide rate rather than a fixed formula — two extensions of identical size can cost very different amounts depending on roof design, structural openings and specification.
Last updated 17 August 2026
| Range | ||
|---|---|---|
| General UK rate | £1,800–£3,000 | Per m² |
Sources: HomeOwners Alliance (2026 guide), Checkatrade (updated June 2026), Checkatrade (general building rate, updated December 2024)
Key points
- A single per-m² figure hides a lot: two extensions the same size can cost very differently depending on roof complexity, glazing and finish specification.
- Per-m² rates tend to fall slightly as the extension gets larger, since fixed costs (like groundworks setup) are spread over more floor area.
- Region matters — the ranges here are general UK figures; London and the South East typically run higher.
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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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.
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