Loft conversion budget estimator
Get a rough loft conversion budget from the floor area and conversion type — rooflight, dormer or hip-to-gable conversions have quite different typical costs.
Result
Base budget
Total budget with contingency
How to use this tool
- Measure the usable loft floor area for the conversion.
- Pick the conversion type closest to your plan.
- Read the base and contingency-adjusted budgets.
Assumptions
- The £1,400/m² rooflight, £1,800/m² dormer and £2,000/m² hip-to-gable rates are illustrative inputs, not quotes or published per-m² prices. They produce different example totals because the selected conversion type changes the rate; real costs depend on region, roof structure, design and finish.
- Does not include planning permission, party wall agreements, building control fees or a staircase relocation if needed.
Sources & reference data
Technical details: what the fields mean
- Loft floor area
areaM2 - Usable floor area of the converted loft space.
- Conversion type
conversionType - Rooflight (Velux-style, no roof structure change) is typically cheapest. Dormer adds a box structure for more headroom/space. Hip-to-gable extends a hipped roof to a gable end, typically the most involved.
- Contingency
contingencyPercent - Extra budget for unexpected structural issues, common in loft work.
Methodology
Base budget = area × typical rate for the chosen conversion type. Total = base budget × (1 + contingency%).
Worked example
30m² dormer loft conversion, 15% contingency
Inputs: Loft floor area: 30 m², Conversion type: dormer, Contingency: 15%
Result: £54,000 base, £62,100 with contingency
Practical guidance
- Check whether your roof structure needs a structural engineer's assessment before committing to a dormer or hip-to-gable design.
- Use the conversion type that matches the proposed design when comparing scenarios; these illustrative rates do not specify a real project. Compare quotes for the same scope and check separately for staircase changes, fees and approvals.
Common mistakes
- Assuming rooflight-conversion pricing applies to a dormer or hip-to-gable project, which typically cost more.
- Forgetting to budget for the staircase and any knock-on changes to the floor below.
FAQs
How much does a 30m² dormer loft conversion cost?
At a rough £1,800/m² with 15% contingency, about £62,100 — get real quotes, as this varies significantly by region and roof structure.
Last reviewed: 2026-10-11
A rough starting-point estimate, not a quote. This is not financial or investment advice.
This tool provides an indicative estimate, based on the assumptions stated above.
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