Loft Conversions

On typical London jobs priced on our estimator in October 2026, all ex VAT: rear dormer loft conversions land between £68,000 and £81,000. One forming a bedroom and shower room, about 20 m² of new floor at a high specification, priced at around £70,000, and a larger one with an en suite, about 28 m² of new floor at a standard specification, priced at around £78,000. Both include party wall matters and a new stair, and both price windows, rooflights, sanitaryware and tiles for fitting only, with the products supplied by you. Rooflight conversions usually cost less than a dormer; mansard and hip to gable conversions usually cost more. The rest depends on the roof space, the type of conversion and the specification, which is why the instant estimator prices yours in minutes and sends a realistic range to your inbox. Figures are indicative.

Each type suits a different roof and budget:

• A rooflight conversion: the roof left as it is, with windows set into its slope; usually the least costly where there is already enough headroom.
• A rear dormer: a box built out from the rear slope, the typical London choice, adding real headroom for a moderate uplift.
• A hip to gable: the sloping side of the roof rebuilt as a vertical gable, for semis and end of terraces, often with a rear dormer. See hip to gable loft conversions.
• A mansard: the rear slope rebuilt almost vertical, the most space and usually the most cost. For a flat at the top of a mansion block, see mansion block loft conversions.

Our guide to Victorian loft conversions shows how these work on a London terrace.

Many loft conversions are permitted development, within volume allowances of 40 cubic metres for a terraced house and 50 for a semi detached or detached house, with conditions on materials and on the roof slope facing the road. Permitted development does not apply in conservation areas, can be removed by local conditions and does not cover flats, so a loft in a flat, or a scheme beyond the allowances, needs an application. Building regulations approval always applies, and party wall notices where the work touches a shared wall. We check the position for your house and manage it.