Standard permitted development depth limits
Under Class A of the GPDO, single-storey rear extensions are permitted development without any planning application up to these depth limits: 4m projection from the original rear wall on a detached house; 3m projection on any other house (semi-detached, terraced, end-of-terrace). The 'original rear wall' means the rear wall of the house as it was first built — not the current rear wall after any previous extensions. Other PD constraints apply: maximum eaves height 3m within 2m of a boundary; maximum overall height not exceeding the existing house roof; materials of similar appearance; the extension must be at the rear of the property, not the front or side principal elevations. Double-storey extensions are never PD — full planning required.
Larger Home Extension prior approval — up to 8m or 6m
The Larger Home Extension (LHE) scheme allows single-storey rear extensions deeper than the standard PD limits — up to 8m on a detached house, up to 6m on any other house. The process: (1) Apply to the local authority for prior approval (a lightweight application, not full planning, fee £120 approx); (2) The authority notifies neighbours, who have 21 days to object; (3) If no objections, prior approval is granted automatically; (4) If objections are received, the authority assesses whether the extension would have an unacceptable impact on the amenity of adjoining occupiers, and must respond within 42 days. The test is narrow — amenity only, not design quality or planning policy compliance — so refusals are rare in practice. Total process 6–10 weeks.
When PD or prior approval is not available
PD and the LHE scheme are not available where: the property is a flat or maisonette (no PD rights at all); the property is listed (any external alteration needs Listed Building Consent); the property is in a conservation area (most PD rights restricted, full planning typically required); an Article 4 Direction applies (council has formally removed PD rights — common in conservation areas); PD rights were removed by planning condition when the property was built (some newer estates have this). London has very extensive conservation coverage — large parts of Hackney, Islington, Camden, K&C, Westminster, Wandsworth, Hammersmith and others. Always check your address for conservation status before assuming PD is available.
