Loft Conversion Cost Calculator
Estimate the cost of converting your loft into a bedroom, office or bathroom — by conversion type, floor area and finish quality, with a full cost breakdown and typical price range.
Estimate only. These are indicative 2026 UK estimates based on typical build rates — this is not a quote. Actual costs vary by region, access, structural condition and planning requirements. Always get itemised quotes from local builders before committing to a project.
Typical range: £41,616 – £56,304
- Build cost
- £42,500
- Staircase
- £2,000
- Architect / design fee (8%)
- £3,560
- Building control
- £900
- Estimated total cost
- £48,960
How loft conversion costs are calculated
Loft conversion cost mainly depends on the type of conversion: a rooflight (Velux) conversion needs no change to the roofline and is cheapest; a dormer adds headroom and floor space; hip-to-gable and mansard conversions alter the roof structure and cost the most. We multiply an indicative build rate per square metre by your floor area and finish quality, then add a staircase allowance, an optional ensuite, building control fees and a design/architect fee. Treat the result as a starting point for budgeting — always get itemised quotes from local builders, as ground conditions, party wall agreements and planning requirements can all change the price.