Loft conversions in Hillingdon

Hillingdon's roof policy

Policy DMHD 1 says roof extensions should:

• be on the rear elevation only;
• be subservient to the existing roof and no more than two-thirds of its average width;
• sit below the ridge and keep a substantial part of the original roof slope above the eaves; and
• use materials and details that match the house.

The council will not support over-large roof extensions, including converting a hipped roof to a gable, and raising the main ridge will generally not be supported. Its supporting guidance adds that, as a guide, roof extensions should not cover more than a third of the main roof, and that dormers should be no larger than the first-floor windows. In conservation areas and Areas of Special Local Character, roof extensions must be traditional rear dormers, kept well within the roof slope.

Permitted development is often the practical route

Because the policy is strict, hip-to-gable and full rear dormer conversions in Hillingdon are usually only achievable under permitted development: up to 50 cubic metres on a semi-detached or detached house. Check that your house keeps its rights, and consider a lawful development certificate. Either way, any new side-facing windows should be high-level, obscure-glazed and non-opening below 1.8 metres above the floor under Hillingdon's guidance.