Do I need planning permission for a loft conversion in London?

Most London loft conversions in houses do not need planning permission — they fall under permitted development (Class B of the General Permitted Development Order), provided the new roof space stays within 40 m³ for terraced houses or 50 m³ for detached and semi-detached houses, the extension does not sit forward of the principal roof slope facing a highway, and materials are similar in appearance to the existing house.

When you DO need planning permission

• You live in a flat or maisonette. Permitted development rights for roof extensions apply to houses only — every loft conversion in a flat needs a planning application.
• You are in a conservation area. Roof extensions are excluded from permitted development in conservation areas. Conservation areas cover a large share of inner London — check your borough's map before designing.
• An Article 4 direction applies. Boroughs can withdraw permitted development rights street by street; Article 4 directions are common in London's historic neighbourhoods.
• The house is listed. Listed building consent is needed for internal and external works, in addition to any planning permission.
• You've used up the volume allowance. Previous roof additions count against the 40/50 m³ limit — including ones made by previous owners.

Even permitted development has conditions

Side-facing windows must be obscure-glazed and non-opening below 1.7 m; the extension cannot overhang the outer face of the original wall; verandas and balconies are not permitted development. Many owners obtain a lawful development certificate from the borough before building — it is not compulsory, but it proves lawfulness when you sell.

How long does it take?

A lawful development certificate or a householder planning application both carry a statutory 8-week target. Actual decision speeds vary significantly by borough — see our borough statistics and the decision-speed league table for current median times.

This guide is general information, not advice on a specific property. Rules change and boroughs differ — always confirm with your borough before committing to a design.