UK House Extension Cost Per m² in 2026: London vs. Regional Breakdown
By Majid Farooq | Updated October 5, 2026
⚡ Quick Answer
Detailed 2026 UK building cost guide per square metre (m²) for single-storey, double-storey, and wrap-around extensions, including Part L insulation upgrades, RSJ steelwork, and VAT.
Planning a house extension in the UK in 2026 requires accurate per-square-metre benchmarking. Since the updated Part L Building Regulations increased thermal efficiency standards for Cavity Wall U-values (0.18 W/m²K) and glazing, base shell build costs have stabilised between £1,900 and £3,100 per m².
2026 UK Extension Cost Per m² by Region (Excl. Kitchen Fit-Out)
| UK Region | Basic Spec (£/m²) | Mid-Range Spec (£/m²) | High-End Architect Spec (£/m²) |
|---|---|---|---|
| North England, Scotland & Wales | £1,750 – £2,050 | £2,050 – £2,400 | £2,500 – £3,000 |
| Midlands, Yorkshire & South West | £1,900 – £2,200 | £2,200 – £2,600 | £2,700 – £3,250 |
| South East & Home Counties (M25) | £2,200 – £2,550 | £2,550 – £2,950 | £3,100 – £3,750 |
| Greater London Boroughs | £2,450 – £2,850 | £2,850 – £3,400 | £3,500 – £4,400+ |
Professional Fees Checklist (Add 12% to 15%)
In addition to your main contractor quote, budget £1,200–£2,500 for RIBA/CIAT architectural drawings, £600–£1,200 for structural engineer RSJ beam calculations, £650–£1,100 for Local Authority Building Control inspection fees, and £900–£1,800 per neighbour if a Party Wall Award is required.
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