Home / Cost guides / Loft conversion cost
How much does a loft conversion cost in the UK?
From around £20,000 for a simple rooflight conversion to £90,000 or more for a mansard. Here is how the main types compare, and a calculator for a rough budget.
Rough build cost
- Budget range
- –
- Rate per m²
- –
- Typical build time
- –
Excludes VAT, professional fees, party wall costs and an en-suite fit-out. A rough guide only. A measured estimate from your drawings will be far tighter.
Get a measured estimateLoft conversion costs by type
Typical 2026 costs outside London, before VAT, for a finished conversion with a new staircase.
| Type | Typical cost | Build time |
|---|---|---|
| Rooflight (Velux) | £20,000–£45,000 | 4–6 weeks |
| Rear dormer | £35,000–£70,000 | 6–8 weeks |
| Hip-to-gable with dormer | £50,000–£80,000 | 6–10 weeks |
| Mansard | £60,000–£90,000+ | 8–12 weeks |
Rooflight (Velux)
The roof shape stays the same and windows go into the existing slope. It's the cheapest option, but only works where there is already enough head height.
Rear dormer
A box-shaped extension off the rear slope gives full-height walls and much more usable floor. It's the most common type on terraced and semi-detached houses.
Hip-to-gable
The sloping side of a hipped roof is built up into a vertical gable wall. It's usually combined with a rear dormer on semis and detached houses with hipped roofs.
Mansard
The rear slope, and sometimes the front, is rebuilt almost vertical. It gives the most space but nearly always needs planning permission, and costs the most.
What pushes the price up
- Steelwork. Most dormers and hip-to-gables need steel beams to carry the new roof and floor.
- Head height. Too little height can mean lowering the ceilings below or rebuilding more of the roof.
- Bathrooms. An en-suite adds plumbing, drainage runs and fittings.
- Fire safety. A protected escape route, fire doors and mains-wired smoke alarms are needed to meet building regulations.
- Stairs. A basic new staircase is often £1,000–£1,500. Bespoke stairs cost much more.
Common questions
How much does a loft conversion cost in 2026?
Outside London, a simple rooflight (Velux) conversion typically costs £20,000 to £45,000, a rear dormer £35,000 to £70,000, a hip-to-gable with dormer £50,000 to £80,000 and a mansard £60,000 to £90,000 or more. London prices are noticeably higher.
Is my loft high enough to convert?
A common rule of thumb is at least 2.2m from the top of the ceiling joists to the underside of the ridge. Less than that usually means a dormer, a mansard or lowering the ceiling below, all of which add cost.
Do I need planning permission for a loft conversion?
Many loft conversions are permitted development, within volume limits of 40 m³ for terraced houses and 50 m³ for semi-detached and detached houses. Mansards and front dormers usually need planning. All loft conversions need building regulations approval.
How long does a loft conversion take?
Roughly 4 to 6 weeks for a rooflight conversion, 6 to 8 weeks for a dormer and 6 to 10 weeks for a hip-to-gable, once work starts.
Pricing a loft conversion?
Send us the drawings and we measure every item, from steels and joists to plasterboard and fire doors, and price it at current rates. Back in 3–5 working days.