Loft conversions cost in London (2026)

Prices reviewed November 2026

The typical price in London is £35,000 to £55,000 (velux (rooflight) conversion). Loft conversion prices depend mainly on the type of conversion and how much structure has to change.

💷 Typical loft conversions prices in London

Typical London prices in 2026. A guide only; your quotes will depend on the job.
Velux (rooflight) conversion	£35,000 to £55,000
Dormer loft conversion	£55,000 to £85,000
Mansard conversion	£70,000 to £110,000

What changes the price

The type: rooflight, dormer, hip-to-gable or mansard.
The roof structure and head height already there.
Stairs and where they can go.
The number of rooms, bathrooms and windows.
Party wall agreements and building control.

How long it takes

A loft conversion usually takes around six to twelve weeks of building work, and longer once design, approvals and the structural engineer's calculations are included.

How to pay less

Check the roof shape early, since it limits which conversions are possible.
Plan the staircase first: it affects the floor below as well.
Compare quotes for the same specification, not just the same type.

Before you hire

Ask whether the loft suits the type of conversion you want, such as Velux, dormer or mansard.
Ask who arranges the structural engineer's calculations and building regulations approval.
Ask whether a party wall notice is needed for a terraced or semi-detached house.
Ask how access, staircase and fire safety are handled in the quote.
Ask to see photos or visit a loft they have finished recently.

💬 Questions about loft conversions costs

Is my loft suitable in London?

Most need about 2.2 metres of head height at the highest point. A builder can check this on a quick visit before you commit to anything.

Do I need planning permission?

Many loft conversions fall under permitted development. Flats, conservation areas and bigger roof changes usually need permission. Ask builders when they quote.

How long will it take?

Often 8 to 12 weeks of building work once approvals are in. Your builder will plan it with you.

Why is a dormer more expensive than a rooflight?

A dormer adds new structure and space, so it needs more materials and labour. A rooflight conversion works inside the existing roof, which costs less but gives less room.

Get loft conversions quotes

Use these figures to plan your budget, then compare written quotes for the same work. Your price depends on the job, the size of your home and how soon you need it. Tell us what you need to request up to 3 local quotes; responses depend on availability.