Why London building costs are different
Building in London costs more than anywhere else in the UK. The premium reflects: labour costs (London trades earn 20–40% more than outside the M25); logistics (ULEZ, Congestion Charge, loading restrictions, parking permits); lead times (longer, less competitive tendering on mid-sized projects); and planning complexity (conservation areas, listed buildings, borough-specific restrictions).
Building costs per m² in London by project type (2026)
New build residential
| Specification | Cost per m² GIA |
|---|---|
| Basic | £2,200–£2,700/m² |
| Mid specification | £2,700–£3,400/m² |
| High specification | £3,400–£4,500/m² |
Rear extension (single-storey)
| Specification | Cost per m² |
|---|---|
| Basic | £1,800–£2,400/m² |
| Mid specification | £2,400–£3,000/m² |
| High spec (bifold doors / lanterns) | £3,000–£4,200/m² |
Loft conversion
| Type | Typical London cost |
|---|---|
| Rooflight only | £25,000–£45,000 |
| Dormer | £55,000–£90,000 |
| Mansard | £85,000–£130,000 |
Full house refurbishment
- Basic refit: £700–£1,100/m²
- Mid-specification: £1,100–£1,600/m²
- High specification: £1,600–£2,500/m²
What drives cost per m² higher
Specification is the biggest single lever. Bifold doors (£8,000–£20,000), a premium kitchen (£20,000–£60,000 supply-only), or underfloor heating (add £80–£150/m²) can significantly increase overall cost per m².
Ground conditions — London clay requires appropriate foundation design. Mini-piles or raft foundations on some sites add £20,000–£60,000 to groundworks costs.