Cost estimator
Whitfield Rear Extension · 480 sq ft · Victorian property
Cost build-up
Materials
Bricks, timber, plasterboard, fixings
£28,400
Labour (in-house)
14 weeks × 3 crew at £55/hr blended
£19,800
Trades (sub-contracted)
Roofing, electrical, plumbing, plastering
£16,200
Overheads
Site setup, scaffolding, skips, insurance
£4,800
Contingency
10%£6,920
Margin
22%£21,470
Suggested project price
£97,590
Healthy margin
Cost breakdown
Materials
£28,400Labour
£19,800Trades
£16,200Overheads
£4,800Contingency
£6,920Margin
£21,470 Foreman AI insight
Victorian rear extensions of this size have historically required 12–15% contingency due to unforeseen structural works. Consider lifting the contingency slider.
Comparable jobs delivered between £82k–£94k.