What permitted development actually is
Permitted development (PD) is a statutory grant of planning permission contained in the Town and Country Planning (General Permitted Development) (England) Order 2015, as amended. It allows specified types of building work — rear extensions up to a certain size, loft conversions of certain forms, outbuildings within set limits — to proceed without a separate planning application. PD is automatic where conditions are met. You don't apply for it; you simply build, having confirmed your project complies. Most homeowners and many contractors confuse PD with a planning permission — it isn't. It's a baseline right to build, subject to many constraints, many of which apply in London.
Class A: extensions
Class A of the GPDO covers single-storey rear extensions and side extensions to dwellinghouses. Key limits in 2026: a single-storey rear extension up to 4m deep on a detached house or 3m on any other house (terraced or semi). Under 'prior approval' (Class A2) those limits double to 8m and 6m respectively, subject to a neighbour consultation. Maximum eaves height 3m; maximum overall height 4m. The extension may not extend beyond a side elevation that fronts a highway. Side extensions: width no more than half the original house, single-storey only, eaves no higher than the existing house. Material must match the existing in finish and appearance. No verandas, balconies or raised platforms.
Class B: loft conversions
Class B covers loft conversions and roof extensions. Permitted development allows up to 40 cubic metres additional volume on a terraced house, or 50 cubic metres on a semi-detached or detached house — this is the cumulative limit including any previous loft additions, not a fresh allowance each time. The additional volume must be at the rear or side of the property; front-facing dormers are not PD and need full planning. The extension must not exceed the height of the existing ridge. No verandas, balconies or raised platforms. Hip-to-gable conversions are PD where they comply with the volume and height limits. Mansards (which add to the front roof slope) are not PD and always need full planning.
Where permitted development doesn't apply in London
Permitted development rights are removed or restricted in several London contexts. Conservation areas (large parts of Camden, Westminster, Kensington and Chelsea, Hackney, Islington, Hammersmith and Fulham): PD often does not apply to side extensions or roof extensions, and rear extensions over a smaller size threshold require full planning. Listed buildings: PD does not apply at all — listed building consent plus planning permission required for any alteration. Article 4 directions: local planning authorities can remove specified PD rights in a defined area — Hackney, Islington, Camden and others have Article 4s on roof additions, painted front doors, hardstanding and other works. Always check your address against the borough's Article 4 register before assuming PD applies.
Flats and maisonettes
Permitted development under Classes A and B applies only to dwellinghouses — houses on their own plot. Flats and maisonettes have very limited PD rights and almost always require full planning for any extension or loft conversion. The owner of a top-floor flat in a converted Victorian terrace cannot proceed under PD for a loft conversion even where the equivalent extension on a house would be permitted. Conversion of a house into multiple flats also requires full planning. London's predominance of flat stock means most PD-eligible projects are owner-occupied houses, not flats.
Lawful Development Certificates (LDCs)
Although PD is automatic, it's strongly recommended (and most lenders, insurers and future buyers require) that you obtain a Lawful Development Certificate from your local planning authority confirming the work was lawful. The LDC is not a planning permission — it's a determination that the work was permitted development and required no application. Cost £103 (statutory fee) plus consultant time; typical determination 6–8 weeks. We include LDC application and management as standard in all our PD projects. Without an LDC, future buyers' solicitors may refuse to proceed, refusing to risk that the work was unauthorised.
Prior approval (Class A2): the 6m/8m option
Where you want to exceed the 3m (semi/terrace) or 4m (detached) baseline rear extension limit, prior approval allows up to 6m or 8m respectively. The process: notify the planning authority of your intent to use PD, who in turn notify neighbours and invite comments. Where no objections are received within 42 days, the extension proceeds. Where objections are received, the planning authority must determine whether the extension's impact on neighbours is acceptable. Approval rate roughly 75–85% in London on prior approval applications — we run a desktop assessment before recommending this route.
