How much does a loft conversion cost?
This is the project where publishers disagree most. Checkatrade and the HomeOwners Alliance put a dormer conversion at £50,000; Rated People's dormer average is £90,000, nearly double. A Velux only conversion starts around £27,500, and large or complex conversions in London can pass £130,000.
£27,500 upwards for a Velux conversion; £50,000–£118,400 for a dormer
The published figures
Every figure below is a published guide figure, shown as its publisher printed it and linked to the source. Retrieved on 17 July 2026.
| What | Published figure | Basis | Source |
|---|---|---|---|
| Velux conversion / dormer / hip to gable | £27,500 / £50,000 / £60,000 | Checkatrade cost guide (opens in new tab) | |
| Per square metre | £1,250–£2,500 per m² | HomeOwners Alliance guide (opens in new tab) | |
| UK average, all types | £55,000–£120,000, minimum from £45,000 | Resi cost guide (opens in new tab) | |
| Main dormer conversion, London | £56,163 | excluding VAT, glazing and fittings | Resi cost guide (opens in new tab) |
| Dormer conversion | £55,500–£118,400, average £90,000 | Rated People cost guide (opens in new tab) | |
| Dormer window / Velux window | £4,500–£6,500 / £900–£1,300 each | Resi cost guide (opens in new tab) | |
| Professional fees: structural engineer | £500–£1,000 | surveyor £500–£1,500, building regulations £700–£1,200 | Resi cost guide (opens in new tab) |
What moves the price
- Conversion type: Velux, dormer, hip to gable or mansard
- Size and number of windows
- Existing roof shape and structural complexity
- Stairs: a simple flight versus a bespoke one
- Professional fees: surveyor, structural engineer, building regulations, party wall
Get real quotes
Guide figures set expectations; only quotes set your price. Compare local businesses on their public evidence:
Sources
- Checkatrade cost guide (opens in new tab) (directory site, published 2026)
- HomeOwners Alliance guide (opens in new tab) (consumer body, published 2026)
- Resi cost guide (opens in new tab) (installer, published 2025-10)
- Rated People cost guide (opens in new tab) (directory site, published 2026)
Figures retrieved from the named sources above on 17 July 2026. Prices change; always confirm with quotes.
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