Velux conversion — from £35,000
A Velux conversion adds roof windows to the existing roof slope without changing the external roof shape. It is the least expensive type of loft conversion and typically does not require planning permission. The main limitation is headroom — if the existing loft has less than 2.3m of head height, a Velux conversion may feel cramped.
A Velux conversion is ideal for creating a single bedroom or study. It is the fastest loft conversion type, typically taking 3–4 weeks from commencement.
Rear dormer — from £45,000
A rear dormer is the most popular loft conversion type in London. It adds a flat-roofed box extension to the rear roof slope, dramatically increasing floor area and headroom. Most rear dormers in London fall within permitted development rights, though properties in conservation areas or on Article 4 land require planning permission.
A rear dormer typically adds a double bedroom and en-suite bathroom, transforming an unusable loft into a comfortable habitable room. Build time is typically 6–10 weeks.
Hip-to-gable — from £50,000
A hip-to-gable conversion is appropriate for semi-detached and end-of-terrace properties where the roof slopes down on the side (the "hip"). The hip is removed and replaced with a vertical gable wall, significantly increasing the floor area of the loft. Often combined with a rear dormer for maximum space.
Mansard conversion — from £70,000
A mansard conversion involves rebuilding the rear roof slope with a near-vertical wall and a flat roof section, creating the maximum possible loft space. It is the most expensive type of conversion but creates the largest and most flexible space. Mansard conversions almost always require full planning permission.
What affects the final cost?
- Property type: Victorian terraces and Edwardian semis are well-suited to loft conversions. Modern trussed roof constructions are more complex and may cost more to convert.
- Structural condition: Properties that require significant structural strengthening — new steel beams, floor strengthening — will cost more.
- Specification: The quality of finishes, bathroom fittings and internal doors significantly affects the final cost.
- Location: Inner London labour rates are higher than outer London. Access difficulties (no parking, narrow streets) add cost.
- Planning and design fees: Architect fees for planning drawings typically add £2,000–£5,000. Structural engineer fees add £1,000–£2,500.
What value does a loft conversion add?
A well-executed loft conversion typically adds 15–25% to a property's value in London. For a £600,000 home, that's £90,000–£150,000 in added value for an investment of £45,000–£65,000. The return on investment is particularly strong in inner west London postcodes where bedroom count has a significant impact on value.