Loft conversion cost in London.
Fulham · SW6 · a bedroom in the roof, with a dormer window and a rooflightCompleted work, photograph
What a dormer or mansard loft costs in London in 2026. From our own cost guide.
Two figures cover most London lofts.
A loft conversion in London is priced from the roof, the stair and planning. We are NU Projects, design and build in Fulham SW6 since 2010. A main dormer loft typically runs £90k to £140k. A mansard loft runs £140k to £220k. Call 020 7731 6841, and a budget estimate typically follows within seven days.
Two figures from our 2026 cost guide cover most London lofts. Both are project totals, not rates.
A main dormer loft typically runs £90k to £140k. It adds a bedroom suite or office level, with a better stair.
A mansard loft typically runs £140k to £220k. The roof is rebuilt for volume, so planning and heritage detail apply.
Where you land depends on the roof, the stair and the finish. A loft bathroom moves it too.
Work to the floors below is priced as its own line. The new stair takes space from them.
Our own quantity surveyor prices every loft, open book, from the drawings.
What the work includes
- A budget estimate, typically within seven days
- A cost plan priced line by line from the drawings
- Dormer and mansard options priced side by side
- Work to the floors below shown as its own line
- Fees, contingency and VAT set out separately
- Planning, building control and party walls handled
- Sources
- Planning Portal, loft conversions, GOV.UK permitted development technical guidance. Figures from our 2026 cost guide. Planning rules read on 21 October 2026, for England.
- What it costs
- See a range in a minute. Then send us the address for a proper number. Open the calculator
- Where we work
- Fulham, Chelsea, Kensington, Knightsbridge, Belgravia, Mayfair, Notting Hill and Holland Park, Chiswick, Wandsworth, Putney and Barnes, Hampstead and St John’s Wood, Weybridge, Cobham and Oxshott, South Kensington, Marylebone, Bayswater and Maida Vale, Pimlico and Westminster, Battersea and Clapham, Richmond, Twickenham and East Sheen, Islington, Highgate and Primrose Hill, Greenwich, Dulwich, Camden, Wimbledon, Bermondsey, Brixton, Ealing, Acton, Hammersmith and Brook Green, Earl’s Court, Queen’s Park and Kensal Rise, Fitzrovia and Bloomsbury
A dormer from £90k. A mansard from £140k.
What moves the cost of a loft.
- 01
Head height
A measured section tests usable height after insulation and the floor build-up.
- 02
Dormer or mansard
A mansard rebuilds the roof, so it costs more than a dormer.
- 03
The stair
Its position changes rooms on the floor below, and their cost.
- 04
Structure
Do not assume the existing ceiling joists can carry a new floor.
- 05
A loft bathroom
Water pressure, drainage falls and ventilation all need checking.
- 06
Fire safety
A new storey changes the escape strategy for the floors below.
- 07
Comfort in summer
Insulation, glazing, shading and ventilation, designed together.
- 08
The planning route
Permitted development or planning permission changes time and fees.
- 09
Party walls
Steel tied into a shared wall needs party wall notices.
- 10
Scaffold and access
Never assume a neighbour will allow scaffold on their land.
Dormer or mansard, what changes.
Both figures are project totals from our 2026 cost guide. Fees, contingency and VAT are extra.
| Question | Main dormer loft | Mansard loft |
|---|---|---|
| 2026 cost guide total | £90k to £140k | £140k to £220k |
| What it adds | A bedroom suite or office level, with a better stair | A rebuilt roof level, for more volume |
| Planning | Often permitted development, outside conservation areas | Almost always planning permission |
| What moves the cost | Head height, the stair and a bathroom | The roof rebuild, heritage detail and planning |
What a loft conversion costs in 2026.
£90k to £140kMain dormer loft. A project total, from our 2026 cost guide.
£140k to £220kMansard loft. A project total, from our 2026 cost guide.
Head height, the stair and the roof form decide where you land.
A loft bathroom and work below are priced as separate lines.
Professional fees, statutory costs, party wall, contingency and VAT are separate. Ranges are guide prices, not fixed quotations.
What owners ask about loft costs.
Further reading, from the journal
Is there enough headroom for a loft conversion?
A measured section tests usable standing height, floor buildup, insulation and stair arrival. Roof height alone does not tell you how useful the finished room will be.
A main dormer loft typically runs £90k to £140k. A mansard loft runs £140k to £220k.
Can I add a bathroom in the loft?
We check hot and cold water, pressure, drainage falls and ventilation. Structural loads and the layout are checked at the same time.
The position can have knock-on effects on the floors below.
Will the existing floors or foundations need strengthening?
The engineer assesses the additional loads and the altered structure. Do not assume existing roof or ceiling joists can carry a new floor.
How much does a loft conversion cost in London?
Our 2026 cost guide puts a main dormer loft at £90k to £140k.
A mansard loft runs £140k to £220k.
Both are project totals, before fees, contingency and VAT.
Why does a mansard cost more than a dormer?
A mansard rebuilds the roof slope for more volume.
It almost always needs planning permission, and heritage detail often applies.
Do I need planning permission for a dormer loft?
Not always. A rear dormer can be permitted development, within volume limits.
The limit is 40 cubic metres on a terraced house, and 50 on others.
In a conservation area, those permitted development rights do not apply.
Does the loft price include fees and VAT?
No. Professional fees, statutory costs, party wall, contingency and VAT are separate.
Our quantity surveyor sets each one out as its own line.
How do I get a firm price for my loft?
Send the address. A budget estimate typically follows within seven days.
A cost plan, priced line by line from the drawings, follows before you sign.
Tell us about the loft.
Your name and one way to reply are enough. It goes straight to the studio.
- Already have an architect or designer? We build to their design. Working with your designer