Guide · Greater London
Loft conversion cost in London
Indicative 2026 price ranges for the four loft types we build most across London, what moves the budget, and how long each takes on site. Figures are guide ranges for planning purposes — every house and postcode prices differently.
Cost by loft type
| Type | Typical cost | On site | Notes |
|---|---|---|---|
| Velux / rooflight conversion | £30,000 – £48,000 | 5–7 weeks | No change to the roof shape. Cheapest route where head height already works. |
| Dormer loft conversion | £50,000 – £78,000 | 7–10 weeks | The London default — a rear box dormer adds full-height floor space and an en-suite. |
| Hip-to-gable + rear dormer | £68,000 – £95,000 | 9–12 weeks | For end-of-terrace and semi-detached homes; largest gain in usable area. |
| Mansard loft conversion | £85,000 – £130,000 | 12–16 weeks | Common in conservation areas. Near-vertical rear wall, almost always needs planning. |
What drives the price
- Structure
- Steel beams, new floor joists and any padstone works into party walls.
- Staircase
- Where the new stair lands often forces changes on the floor below.
- Bathrooms
- An en-suite adds drainage runs, waterproofing and fit-out cost.
- Planning
- Permitted development vs full planning, plus party wall awards with neighbours.
- Access
- Narrow London streets, scaffold licences and skip permits all carry a cost.
- Finish level
- Joinery, glazing and sanitaryware specification move the budget most.
Common questions
How much does a loft conversion cost in London?
Most London loft conversions land between £50,000 and £95,000. A simple rooflight conversion can start near £30,000, while a mansard in a conservation area can pass £120,000.
Do I need planning permission for a loft conversion?
Many rear dormers fall under permitted development, but conservation areas, flats and mansards normally need full planning permission. A party wall award is usually needed for terraced and semi-detached homes.
How long does a loft conversion take?
Typically 6 to 12 weeks on site for a dormer, and up to 16 weeks for a mansard, plus 8 to 12 weeks beforehand for design, planning and party wall notices.