Extension Cost Calculator

Estimate the build cost of a home extension or conversion. Useful for budgeting before commissioning architectural drawings or surveys.

Extension type

Floor area added

m²

Build quality

Region

Kitchen fit-out

£

Bathroom / en-suite

£

Bi-fold doors

m

£ /m

Roof lantern

qty

£

Underfloor heating

£ /m²

Design fees (architect, structural engineer) 10% of build Building Regs fees £700 Planning application (if needed) £258 householder fee Party Wall awards × £1,500 each neighbour Contingency (10%) Recommended for renovations VAT (20%) Standard rate for extensions

Number of party wall neighbours

ESTIMATED TOTAL COST

£0

Rate applied: £0/m²

Likely range: £0 - £0

Cost breakdown

Indicative only. Based on representative £/m² rates by extension type, quality and region. Actual costs depend heavily on specification, site conditions, and contractor. Commission detailed quotes from at least three builders before committing.
VAT: extensions to existing dwellings are standard-rated at 20%. New self-build dwellings may be zero-rated.