Compare Velux, dormer, hip-to-gable and mansard costs →
What affects the cost?
Current Checkatrade 2026 benchmarks vary sharply by conversion type. For a typical 30m² project, a Velux conversion is around £22,500–£30,000, a dormer £40,000–£60,000, hip-to-gable £50,000–£70,000 and mansard £50,000–£80,000. Roof structure, staircase position, usable area, structural steel, bathroom specification and location are major variables.
- Velux, dormer, hip-to-gable, mansard or shell-only type
- Usable new floor area
- Roof structure and existing head height
- New staircase position and specification
- Structural steel and roof alterations
- Ensuite, electrics, heating and finish level
- Region, access and scaffolding
Typical cost breakdown
Regional planning examples
The examples below apply our published modelling factor to the same national benchmark. They are not claimed as observed city-wide average quotes.
Loft conversion costs by location
Open a detailed city page to see the same national benchmark adjusted through the transparent regional model, with local planning considerations and worked examples.
Sources used for this guide
Loft Conversion Cost: 2026 UK Price Guide & Breakdown
Published / checked: March 2026
Used for: Loft conversion type benchmarks
Construction output price indices
Published / checked: 13 August 2026
Used for: Construction price trend and update checks
Frequently asked questions
How much does a dormer loft conversion cost in 2026?
Checkatrade’s current 2026 table gives about £40,000–£60,000 for a typical 30m² dormer, with an average around £50,000. Size, region, staircase work and specification can move a real quote outside this range.
What is the cheapest type of loft conversion?
A Velux or rooflight conversion is usually the lowest-cost option because it retains more of the existing roof shape. Checkatrade’s 30m² benchmark is about £22,500–£30,000.
How much is a mansard loft conversion?
The current 30m² benchmark is about £50,000–£80,000, with an average around £65,000. Mansards involve substantial roof reconstruction, so planning and structural complexity can be significant.
Does a loft conversion need Building Regulations approval?
Yes. Loft conversions must comply with Building Regulations. Planning permission requirements depend on the property and proposed roof alterations, so check the project-specific position before work starts.
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