The permitted development rules for rear extensions
On a house, a single-storey rear extension is permitted development if it projects no more than 3 m from the original rear wall on a terraced or semi-detached house, or 4 m on a detached house, is no higher than 4 m, has eaves no higher than 3 m where it comes within 2 m of a boundary, and uses materials similar in appearance to the house. The larger home extension route allows 6 m or 8 m through a 42-day prior approval, where the council consults the neighbours.
Flats and maisonettes have no householder permitted development rights, so any rear extension to a flat needs planning permission. Previous extensions count against the allowance, and the larger home extension route is not available in conservation areas.
What changes in Lambeth
In a conservation area a single-storey rear extension can still be permitted development within the 3 m or 4 m limit, but cladding it in materials that differ from the house is not, and the 6 m and 8 m prior approval route is closed.
The local constraints that most often decide the route in Lambeth are listed below, taken from our Lambeth area page. Each one is a reason to confirm the address on Lambeth's constraints map before relying on permitted development.
- Conservation areas. Lambeth has numerous conservation areas covering much of Kennington, Stockwell, Clapham, Brixton, Herne Hill and Streatham. Roof extensions and cladding in these areas need planning permission rather than permitted development. Check the council's constraints map for your address before assuming PD applies. Source
- Article 4 directions. Lambeth has Article 4 directions in a number of conservation areas removing permitted development for front alterations and boundary treatments, and a Class MA Article 4 covering Waterloo, Vauxhall and other central and town-centre locations that removes the commercial-to-residential prior approval route. We confirm coverage for your address with the council.
- Thames flood zones. Waterloo, Vauxhall, Nine Elms and the riverside at Lambeth fall within Flood Zones 2 and 3, protected by the Thames Barrier and river walls. Basements and new ground-floor habitable rooms there may need a flood risk assessment; surface water flooding is also a recorded issue in parts of Herne Hill and Streatham. Source
- Listed buildings and the Kennington and Clapham set pieces. Kennington, Clapham Old Town, Stockwell and the Vauxhall riverside contain many listed Georgian and Victorian houses and terraces. Listed houses need listed building consent for almost any alteration, and the setting of listed terraces is considered for extensions to neighbours.
- Metropolitan Open Land. Clapham Common, Brockwell Park, Streatham Common and Norwood Park are Metropolitan Open Land. Houses fronting or backing onto them are judged on the effect of extensions and outbuildings on openness and setting.
What Lambeth planning officers look for
Lambeth's officers apply the Local Plan's residential design and amenity policies fairly predictably. Rear extensions deeper than neighbouring precedent, side returns that breach the 45-degree rule to the neighbour's rear window and roof extensions in conservation areas are the common refusal reasons. Mansards are accepted on terraces where the street already has them; front dormers and roof extensions on butterfly-roofed terraces attract resistance. Pre-application advice is available for a fee, and Lambeth's decision times can stretch beyond the statutory period at busy times.
Fees and timelines
The council fee for a householder application is £528 and for a Lawful Development Certificate £264 (England, from 1 April 2025; verify before applying). Both are decided within 8 weeks of validation.
Our own fee for the drawings and the application is fixed once quoted and depends on the project type, its size and the constraints above. Answer six questions in the quote tool and we email you an indicative figure within minutes, then a written fixed-fee quote within 24 hours.
