Side extensions in Sevenoaks depend on the house. Typical homes here: Large detached and Edwardian houses in Sevenoaks town, Kippington, Wildernesse and Riverhead; 1930s and post-war semi-detached houses in Swanley, Hextable, Dunton Green and Otford. Designations to check first: Green Belt; Kent Downs National Landscape; Conservation areas. Applications are decided by Sevenoaks District Council and the Sevenoaks Core Strategy 2011 and Allocations and Development Management Plan 2015.
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 Sevenoaks
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 Sevenoaks are listed below, taken from our Sevenoaks area page. Each one is a reason to confirm the address on Sevenoaks' constraints map before relying on permitted development.
- Green Belt. Most of the Sevenoaks district outside the built-up areas of Sevenoaks town, Swanley, Westerham, Edenbridge and the larger villages is Metropolitan Green Belt. Source
- Kent Downs National Landscape. The Kent Downs National Landscape (formerly the Kent Downs AONB) covers the North Downs across much of the district, including Otford, Kemsing, Shoreham, Westerham and the countryside north of Sevenoaks town. Source
- Conservation areas. Sevenoaks has around 40 conservation areas, including Sevenoaks High Street and The Vine, Westerham, Otford, Kemsing, Shoreham, Edenbridge, Riverhead, Chevening and many smaller village centres. Source
- Knole Park and listed buildings. Knole House and its deer park sit on the edge of Sevenoaks town, and the town, Westerham, Otford, Shoreham, Edenbridge and the villages contain a very high concentration of listed houses, cottages and churches. Source
- River Darent and River Eden flood risk. The River Darent runs from Westerham through Riverhead, Otford and Shoreham, and the River Eden runs through Edenbridge; land alongside both sits in Flood Zones 2 and 3. Source
What Sevenoaks planning officers look for
Sevenoaks officers assess householder applications against the Core Strategy 2011, the Allocations and Development Management Plan 2015 and the council's residential extensions guidance, with Green Belt and Kent Downs policy in the background for most of the district. They tend to look for extensions that stay subordinate to the original house in scale and roof form, side extensions set back from the front wall and below the ridge with a gap kept to the boundary, rear extensions that clear the 45-degree line to the neighbour's nearest habitable window, and dormers set back from the eaves and clad in matching tile. Common refusal reasons are disproportionate Green Belt additions, side extensions that create a terracing effect, and roof extensions or box dormers in conservation areas. Outside the designations, hip-to-gable and rear-dormer lofts within 50 m³ on a semi are routinely lawful and we secure a Lawful Development Certificate as proof.
Fees and timelines
Sevenoaks decides a householder application or a Lawful Development Certificate within 8 weeks of validation. The council fee is £528 for a householder application and £264 for a Lawful Development Certificate (England, from 1 April 2025; verify before applying).
Our own fee is fixed once quoted. The quote tool gives an indicative figure in minutes and a written quote follows within 24 hours.
Primary sources
- The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2: the permitted development limits quoted above.
- Planning Portal: do you need permission: the national guidance and the application service every council accepts.
- Sevenoaks District Council: planning: the council's own constraints map, validation checklist and pre-application service.
