The permitted development rules for side extensions
A single-storey side extension is permitted development on a house if it is no wider than half the width of the original house, no higher than 4 m, with eaves no higher than 3 m where it comes within 2 m of a boundary, and finished in materials similar in appearance to the house.
Anything wider than half the original house, any two-storey side extension, and any side extension on a flat needs planning permission. Garage conversions that keep the walls are usually permitted development; extending beyond them is assessed as a side extension.
What changes in Kingston upon Thames
Side extensions are not permitted development in a conservation area at all, so there a planning application is always required.
The local constraints that most often decide the route in Kingston upon Thames are listed below, taken from our Kingston upon Thames area page. Each one is a reason to confirm the address on Kingston upon Thames's constraints map before relying on permitted development.
- Conservation areas. Kingston has numerous conservation areas, including Kingston Old Town, Surbiton's Southborough and Oakhill areas, Coombe and parts of New Malden. Roof extensions and cladding in these areas need planning permission. Check the council's constraints map for your address before relying on permitted development. Source
- Thames and Hogsmill flood zones. Land along the Thames at Kingston and Canbury and along the Hogsmill through Old Malden, Berrylands and Kingston falls within Flood Zones 2 and 3. Basements and new ground-floor habitable rooms may need a flood risk assessment even for a householder application. Source
- Green Belt and Metropolitan Open Land. Chessington, Hook and the southern edge of the borough include Green Belt, and there is Metropolitan Open Land along the Hogsmill and around Richmond Park. Extensions and outbuildings to houses within or adjoining these areas are judged on openness and are often limited in size.
- Article 4 directions. Some Kingston conservation areas are understood to carry Article 4 directions removing permitted development for front alterations and boundary treatments. Coverage varies by area, so we confirm with the council before recommending a permitted development route.
What Kingston upon Thames planning officers look for
Kingston is a predominantly suburban borough and its officers pay close attention to the character of 1930s streets. Side extensions that close the gap between semis, are not set back from the front wall or carry a roof up to the main ridge are a frequent refusal reason, as are two-storey rear extensions that breach the 45-degree rule to neighbours. Single-storey rear extensions of 3 to 4 m are generally acceptable. Roof extensions in conservation areas and front dormers anywhere attract resistance. Pre-application advice is available for a fee.
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.
