Loft conversion cost by type
Velux (rooflight) loft conversions are the most cost-effective when existing headroom permits — typically £45,000–£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 £55,000–£85,000 for a single-bedroom-plus-en-suite layout. A full-width rear dormer with second bedroom or studio space pushes towards £95,000.
Hip-to-gable conversions on end-of-terrace or semi-detached properties typically run £65,000–£95,000 standalone, or £75,000–£110,000 when combined with a rear dormer. Mansard loft conversions are the most complex and most expensive at £85,000–£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 £3,500–£6,500 combined; planning fees from £258 (or £129 for an LDC); Building Regulations charges £600–£1,200; party wall agreements £900–£1,500 per neighbour; and a 5–10% contingency on the build itself.
For a £75,000 build, that adds £8,000–£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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