Loft conversion cost by type
Velux (rooflight) loft conversions are the most cost-effective when existing headroom permits - typically GBP 45,000-GBP 60,000. No structural alteration to the roof shape is required, which is what keeps the price down.
Rear-dormer loft conversions - the most common type on London terraces - run GBP 55,000-GBP 85,000 for a single-bedroom-plus-en-suite layout. A full-width rear dormer with second bedroom or studio space pushes towards GBP 95,000.
Hip-to-gable conversions on end-of-terrace or semi-detached properties typically run GBP 65,000-GBP 95,000 standalone, or GBP 75,000-GBP 110,000 when combined with a rear dormer. Mansard loft conversions are the most complex and most expensive at GBP 85,000-GBP 120,000+ but deliver the highest floor area and the best ceiling heights.
Beyond the build cost - what to budget
Realistic 2026 additional costs include: architectural and structural drawings GBP 3,500-GBP 6,500 combined; planning fees from GBP 258 (or GBP 129 for an LDC); Building Regulations charges GBP 600-GBP 1,200; party wall agreements GBP 900-GBP 1,500 per neighbour; and a 5-10% contingency on the build itself.
For a GBP 75,000 build, that adds GBP 8,000-GBP 14,000 of additional costs on top. We give clients a full all-in budget at the project review stage rather than just the headline construction figure.
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