Loft conversions
Loft conversions: costs, planning and quotes
Costs for every type of loft conversion, with fees and contingency included, worked out by a quantity surveyor.
- Typical all-in cost
- £35,000 to £95,900
- Rates checked
- November 2026
- Free calculator
- Price your project
- Your details
- Never asked for
What it costs
National baseline prices for a standard finish, including VAT. London is around 25% higher; the North and Northern Ireland lower.
Price your own project| Project | Building work | Fees | Contingency | All-in |
|---|---|---|---|---|
| Velux (roof light) conversion | £29,400 | £2,400 | £3,200 | £35,000 |
| Dormer conversion | £65,100 | £5,200 | £7,000 | £77,300 |
| Hip-to-gable conversion | £75,100 | £6,000 | £8,100 | £89,200 |
| Mansard conversion | £80,000 | £7,200 | £8,700 | £95,900 |
What affects the price
- The type of conversion, which sets how much of the roof is rebuilt
- Head height: you need about 2.2m at the highest point, or the roof must change
- Where the new stairs land on the floor below
- Adding a bathroom, and how far it is from existing pipes
- Steel beams and strengthening the floor
- Scaffolding and access, especially on terraced streets
Do you need planning permission?
Check my projectThese are the rules for houses in England. Flats, listed buildings and conservation areas have tighter rules, and Wales, Scotland and Northern Ireland differ. Check with your council before you build.
- Most loft conversions are permitted development, so they need no planning application, if the added roof space stays within 40 cubic metres on a terraced house or 50 cubic metres on a semi-detached or detached house.
- Dormers cannot face the road at the front of the house, should sit back about 20cm from the eaves, and should use materials that match the house.
- Mansards, and any conversion in a conservation area, usually need full planning permission.
- Every loft conversion needs building regulations approval for the structure, fire escape and stairs, and semis and terraces usually need a party wall agreement.
Loft conversion guides
Guides for this topic are being written.
Getting quotes
How to find a good loft specialist
A fair price starts with comparing the same job across several firms.
- Ask for three quotes from the same drawings. Without a shared specification, each firm prices a different job.
- Check each firm before you invite it. Look it up at Companies House, ask to see its insurance certificate, and speak to a recent customer. TrustMark, the government-endorsed scheme, lists registered firms.
- Compare what is included, not just the total. Our quote checker shows how a quote compares with our estimate and what it leaves out.