Loft Conversion Costs in London 2025

A loft conversion in London typically costs between £35,000 and £80,000 depending on the type, size and specification. Here is a breakdown of the main loft conversion types and their typical costs in 2025.

Dormer Loft Conversion Cost

A dormer loft conversion is the most popular type in London, typically costing £40,000–£60,000. A rear dormer adds a box-shaped extension to the back of your roof, creating a full-height room with vertical walls and a flat or pitched roof.

Mansard Loft Conversion Cost

A mansard conversion is more extensive, typically costing £50,000–£80,000. It involves altering the roof structure to create a near-vertical rear wall, maximising headroom and floor space. Mansard conversions usually require planning permission.

Hip-to-Gable Loft Conversion Cost

A hip-to-gable conversion suits semi-detached and detached houses with a hipped roof. Costs range from £45,000–£70,000. This type extends the gable end wall to create more floor space.

What Affects the Cost?

• Type of conversion (dormer, mansard, hip-to-gable, Velux)
• Size of the loft space
• Specification of finishes
• Structural work required
• Planning permission fees (if required)
• Building regulations fees
• Location within London

Frequently Asked Questions

Do I need planning permission for a loft conversion?

Most loft conversions in London fall under permitted development rights and do not require planning permission, as long as they meet certain limits and conditions. Mansard conversions typically do require planning permission. Crown Architecture will advise you on whether your project needs permission.

How long does a loft conversion take?

A typical loft conversion takes 8–12 weeks to complete once the planning and building regulations approvals are in place. The design and planning phase typically takes 6–12 weeks before work can begin on site.

Does a loft conversion add value to my home?

Yes — a loft conversion typically adds 15–25% to the value of your home in London. It is one of the most cost-effective ways to add space and value.