Cost guide
What's the cost per square metre for an extension?
The per-m² method explained, and the published UK rate.
Our own rate for an extension runs £1,600-£3,500 per m² excluding VAT, depending on specification tier - use the cost calculator for a figure based on your project. For general UK market context, 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 | ||
|---|---|---|
| Our rate (all specification tiers) - our confirmed rate, excl. VAT | £1,600-£3,500 | Per m² |
| General market rate | £1,800-£3,000 | Per m² |
Sources: HomeOwners Alliance (2026 guide), Checkatrade (updated June 2026), Checkatrade (general building rate, updated December 2024)
These are general UK ranges. We build across the North West, including Darwen, Blackburn and the wider Lancashire and Greater Manchester area - site access, local trade rates and travel distance can move your actual price within (or occasionally outside) the range above.
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.
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Common questions
What's the cost per square metre for an extension? FAQs
Is this a fixed quote for my What's the cost per square metre for an extension??
No. The figures above are published UK industry ranges from HomeOwners Alliance and Checkatrade and Checkatrade, not a quote for your project. An accurate price depends on a site survey and your specific requirements - get in touch for an estimate based on your own project.
What actually drives the price up or down?
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.
What's a typical our rate (all specification tiers) in per m² terms?
Our rate (all specification tiers) typically runs £1,600-£3,500 (per m²), for a our confirmed rate, excl. VAT, based on the sources cited above.
Other cost guides
More published cost ranges
How much does a house extension cost?
The published UK per-m² rate for a single-storey extension, and what actually moves it.
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 planning permission cost?
The current government application fee, and what else typically adds to the cost.
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