Estimate the cost of a dormer or Velux loft conversion in the UK by property type, size and finish level.
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How This Works
Loft conversion costs vary by type: Velux (rooflight only, no structural changes): cheapest at £1,000–1,500/m². Dormer: adds floor space and headroom with a structural extension of the roofline. Hip-to-gable: removes the sloping hip and replaces with a vertical gable wall — often combined with a dormer. Mansard: the most extensive conversion, requiring planning permission.
Not always. Velux/rooflight conversions almost always fall under Permitted Development (PD) — no planning needed. Rear dormers within size limits also usually qualify for PD. However: mansard conversions almost always need planning. Any conversion in a conservation area or listed building needs consent regardless of type. Always check with your local planning authority and get a Lawful Development Certificate as evidence your conversion is permitted.