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Major Capital · Home Extension
UK Loft Conversion Cost 2026 — Type-By-Type, City-By-City
A typical UK loft conversion costs £25,000-£72,000 depending on type — dormer cheapest, mansard most expensive
Published 18 Apr 2026n=1,820Press-citableCC-BY 4.0
Quote
"A mansard loft conversion in inner London now exceeds £96,000 on average — almost the price of a full extension. The loft-conversion premium is now London's largest home-improvement cost line."
— TradeMatch UK Editorial Team
Methodology
How this study was carried out
TradeMatch sampled 1,820 completed UK loft conversions between Q1 2024 and Q1 2026, controlling for conversion type (Velux, dormer, hip-to-gable, mansard) and house type (3-bed semi typical). All projects were Building-Control-signed-off, Part L energy-compliant, with planning permission or permitted-development confirmation.
Sample: 1,820 completed UK loft conversions on TradeMatch, 2024-Q1 to 2026-Q1
Headline Findings
What this study found
- A mansard loft conversion in inner London now costs £96,600 on average — the highest single-project cost in TradeMatch's home-improvement dataset
- Velux-only conversions are 33% cheaper than dormer conversions but yield 30-40% less usable floor space
- Loft conversions add 18-25% to a UK property's value typically — meaning the average dormer (£42,800) returns £45,000-£55,000 in valuation uplift on a £250k home
- Inner-London loft conversions cost 50% above national average — driven by labour, scaffolding, party-wall costs, and neighbourly-disturbance premium
Dataset
TradeMatch UK loft conversion data, 1,820 completed projects, Q1 2024 to Q1 2026
| Conversion Type | UK Avg | Inner London | Northern UK |
|---|---|---|---|
| Velux (rooflight only) | £28,400 | £42,600 | £21,300 |
| Dormer (rear-facing) | £42,800 | £64,200 | £32,100 |
| Hip-to-gable + dormer | £48,600 | £72,900 | £36,500 |
| Mansard (full) | £64,400 | £96,600 | £48,300 |
| L-shape dormer | £52,200 | £78,300 | £39,200 |
Context
Why this matters
UK loft conversions divide into four typical categories. Velux (skylights only, no roof structure change) is the cheapest and only adds usable space without changing the roofline. Dormer (rear-facing protrusion) is the most popular UK conversion. Hip-to-gable converts the hipped end-wall to a vertical gable, recovering significant floor area. Mansard rebuilds the entire roof structure with vertical walls, the most expensive option but creating maximum usable space. Permitted-development limits apply: most rear-dormer conversions on UK semi-detached homes are permitted-development under the GPDO Class B; mansard conversions typically require planning permission.
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Questions
FAQ
Do I need planning permission for a loft conversion?
Most rear-dormer and Velux conversions are permitted development under GPDO Class B (subject to the 40m³ / 50m³ volume limit). Hip-to-gable and mansard conversions in Conservation Areas, Article 4 Direction zones, or on listed buildings typically require planning permission.
Will a loft conversion add value to my home?
Yes — UK property data shows loft conversions add 18-25% to property value typically, more in higher-demand areas. Mansards and dormers add more than Velux conversions due to greater usable floor area.
How long does a UK loft conversion take?
Velux: 4-6 weeks. Dormer: 8-12 weeks. Hip-to-gable + dormer: 10-14 weeks. Mansard: 12-18 weeks. Add 4-6 weeks for design + planning + Building Control submissions before on-site work begins.
Do I need a structural engineer?
Yes — every UK loft conversion requires structural-engineer-approved design (steel beams, floor-joist sizing, party-wall calculations). Typical structural-engineer fee: £1,500-£4,000 on top of the headline conversion cost.
For Press
Cite this study
Citation: TradeMatch UK (2026). UK Loft Conversion Cost 2026 — Type-By-Type, City-By-City. Available at: https://www.tradematch.uk/data/uk-loft-conversion-cost-2026
Granular data and per-postcode breakdowns are available to UK media outlets on request to [email protected]. Released under CC-BY 4.0 — re-use freely with attribution.
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