In 2026, single-storey extensions in England and Wales typically range from £1,800 to £3,500+ per square metre. For a standard 20m² extension, homeowners should anticipate build costs between £36,000 and £70,000+, depending on specification and location.
Cost by build quality
| Build quality | Cost per m² (2026) | Example (20m²) |
|---|---|---|
| Basic build | £1,800–£2,200 | £36,000–£44,000 |
| Mid-range finish | £2,200–£2,800 | £44,000–£56,000 |
| High-end | £2,800–£3,500+ | £56,000–£70,000+ |
Regional cost variations
| Region | Typical cost per m² (mid-range, 2026) |
|---|---|
| London & the South East | £2,800–£3,800 |
| Midlands & East of England | £2,200–£2,800 |
| North of England | £1,800–£2,400 |
| Wales | £1,800–£2,400 |
What to keep in mind
- Builder quotes typically exclude 20% VAT.
- Budget an additional 10–20% for professional fees and contingency.
- London and the South East run 20–30% above the national average.
The cost of your drawings
The figures above are build costs. The drawings you need for planning and building regulations are a separate, much smaller cost. Arkiplan’s fixed-price design packages start from £1,698. You can pay up front, spread it across 3 monthly instalments, or choose monthly payments from £94/month — with no credit checks and no interest. Council application fees (typically £300–£700) are paid directly to your council and are not included.