Loft Conversions in London: Dormer, Hip-to-Gable, or Mansard?

A loft conversion is often the most cost-effective way to add a bedroom and bathroom to a London home. But choosing the wrong type for your property wastes money and can create an awkward, underused space.

Rear Dormer

The most common and usually most affordable option. A rear dormer extends the back slope of your roof vertically, creating full head height across the width of the house. Most rear dormers on terraced and semi-detached houses fall under permitted development.

Best for: terraced houses, semi-detached properties, where you want maximum floor space at minimum cost.

Budget: £45,000–£65,000 depending on size and specification.

Hip-to-Gable

If your roof has a hipped (sloped) side rather than a vertical gable wall, a hip-to-gable conversion extends that side vertically before adding a rear dormer. This creates significantly more usable floor space than a dormer alone.

Best for: semi-detached and detached houses with hipped roofs.

Budget: £55,000–£80,000. The additional structural work and brickwork adds cost but the space gain is substantial.

Mansard

A mansard conversion replaces your entire roof structure with a new profile — nearly vertical walls with a flat top. It creates the maximum possible space and effectively adds a full new storey. Mansards almost always require planning permission.

Best for: properties in areas where planning supports them, terraced houses where you want a full additional floor, and situations where the existing roof structure is poor.

Budget: £70,000–£110,000. The most expensive option but creates the most valuable space.

The Right Choice for Your Property

We assess roof structure, planning constraints, party wall implications, and your space requirements before recommending a conversion type. Sometimes the answer is that a loft conversion isn't the right investment — and we'll tell you that honestly.