How Much Does a House Extension Cost in 2025?
Average cost in United Kingdom
£30,000 - £60,000
Typical average: £45,000
Upload your quote for instant analysis
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?
Extension size (square meters)
Single or double storey
Specification and finishes
Location (London 20%+ more)
Planning and building regs
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
Got a Quote for House Extension?
Upload your quote and our AI will check every line item against local market rates. Find out if you're being overcharged in 30 seconds.