How Much Does a House Extension Cost in 2025?
Last updated: February 2026
Average cost in United Kingdom
Typical average: £45,000
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House Extension Cost by Country
| Country | Low | Average | High |
|---|---|---|---|
| 🇬🇧United Kingdom | £30,000 | £45,000 | £60,000 |
| 🇺🇸United States | $80,000 | $140,000 | $200,000 |
| 🇦🇺Australia | A$80,000 | A$120,000 | A$160,000 |
| 🇨🇦Canada | C$80,000 | C$130,000 | C$180,000 |
House Extension Cost Breakdown
| Item | 🇬🇧 UK | 🇺🇸 US |
|---|---|---|
| Single storey (per sqm) | £1,500-2,500 | $2,500-4,000 |
| Double storey (per sqm) | £1,200-2,000 | $2,000-3,500 |
| Planning application | £200-500 | $500-2,000 |
| Architect fees (10-15%) | £3,000-9,000 | $8,000-20,000 |
| Structural engineer | £500-1,500 | $1,000-3,000 |
What Affects House Extension Cost?
Prices vary significantly by region and provider. For more information about typical general contractor pricing, see our General Contractor invoice auditing page, or browse all cost guides.
Frequently Asked Questions
Extensions under 3m (semi/terraced) or 4m (detached) from the rear wall may be permitted development. Larger extensions, side extensions, and conservation areas require planning permission.
A small single-storey extension takes 10-14 weeks. Larger extensions take 16-24 weeks. Add 8-12 weeks for planning permission if needed.
Extensions typically add 5-10% to home value, but costs vary by area. In premium locations, the value added often exceeds build cost.
Related Cost Guides
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