Cost guide
How much does a rear extension cost?
Published UK ranges for a single-storey rear extension.
A rear extension typically costs £1,800–£3,000 per m² in the UK, according to HomeOwners Alliance and Checkatrade, putting a typical 20-30m² rear extension in the region of £40,000–£84,000. MyBuilder separately quotes £20,000–£40,000 as a total for a straightforward rear extension project.
Last updated 17 August 2026
| Range | ||
|---|---|---|
| General rate | £1,800–£3,000 | Per m² |
| Typical total project | £20,000–£40,000 | Total project |
Sources: HomeOwners Alliance (2026 guide), Checkatrade (general rate, updated June 2026), MyBuilder (published December 2025)
Key points
- How far you extend — permitted development depth limits (4m for a detached house, 3m for others, under the standard rules) are often the practical ceiling before a full planning application is needed.
- Whether the extension opens the ground floor into a kitchen-diner, which usually means removing a structural wall.
- Roof design and how much natural light reaches the rest of the ground floor.
These are general published ranges, not a quote. Get an estimate based on your own project.
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