Side extensions in Richmond upon Thames come mostly from the 1930s semis and bungalows of Whitton, Hampton, Hampton Hill and Ham, where the strip beside the house is the obvious place for another bedroom, a utility room or a converted garage. They also come from the end house of Victorian rows in Twickenham, St Margarets and Mortlake and from Edwardian houses in Kew, Teddington and Barnes. Whichever it is, the council's House Extensions and External Alterations SPD reads the gap between neighbouring houses closely, so the first drawing question is how much space is left beside the extension, not only how much room it adds.
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 Richmond 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 Richmond upon Thames are listed below, taken from our Richmond upon Thames area page. Each one is a reason to confirm the address on Richmond upon Thames' constraints map before relying on permitted development.
- Conservation areas. Richmond has 85 conservation areas, covering a large share of the borough's housing. Source
- Article 4 directions. Many Richmond conservation areas carry Article 4 directions removing permitted development for front elevations, windows, porches, boundary walls and hardstandings. Source
- Thames flood zones. Low-lying land at Barnes, Mortlake, Kew, Twickenham riverside, Teddington and Hampton falls within Flood Zones 2 and 3. Source
- Metropolitan Open Land and Royal Parks. Richmond Park, Bushy Park, Kew Gardens (a World Heritage Site) and Ham Lands are Metropolitan Open Land or protected landscapes.
- Listed buildings. The borough has a high number of listed buildings, particularly around Richmond Green, Richmond Hill, Petersham, Twickenham riverside and Hampton.
What the House Extensions SPD asks of a side extension
Paragraph 5.2.1 of the SPD says side and rear extensions should not dominate the existing house or its neighbours, and offers two ways to achieve that. The extension can be integrated with the house, which it says can work well on detached houses and sometimes at the end of uniform terraces. Or it can read as an obvious addition that is subordinate to the main structure, so the original form can still be appreciated, in which case the ridge of the extension should be set lower than the ridge of the main house.
Paragraph 5.2.2 says that where an extension is to be subordinate it is usually desirable to set it back at least 1 metre behind the front elevation. Paragraph 5.2.3 says development that significantly reduces an important gap between neighbouring houses is not normally acceptable, because combined with neighbours' extensions it can have a terracing effect on the street, and that two-storey side extensions should be sited 1 metre from the side boundary. Paragraph 5.2.1 also says two-storey side and rear extensions should not be greater than half the width of the original building.
Because the SPD sets out these tests for design, they apply whether or not the extension needs planning permission (paragraph 1.1.2). The SPD calls its examples indicative of the council's approach, not a fixed formula.
Local Plan policy, conservation areas and Article 4 directions
Richmond adopted a new Local Plan on 7 October 2025, which replaced the 2018 plan's policies. Two of its policies bear on a side extension. Policy 28 requires development to be of high architectural and urban design quality and compatible with local character, including development patterns, scale, massing, proportions and materials. Policy 46 protects the amenity of neighbouring properties, including daylight and sunlight, outlook, privacy and avoiding a visually intrusive or overbearing impact, and expects applicants to have regard to the House Extensions and External Alterations SPD. The council's SPD page says adopted SPDs remain in force.
The council says Richmond contains 85 conservation areas. Its conservation area FAQ lists front and side extensions of one storey or more among the permitted development rights restricted for single dwellings in them, and says flats and houses converted into flats have no permitted development rights at all. Article 4 directions in these areas restrict further works to the outside of single homes, and some cover only part of an area or only certain works, so the direction for the specific street needs checking.
What Richmond upon Thames planning officers look for
Rear extensions deeper than neighbouring precedent, roof extensions that are not clearly subordinate, and front dormers are common refusal reasons. Side extensions on suburban semis are expected to be set back and lower than the main roof so the gap between houses reads. In conservation areas expect detailed comments on windows, brick and rainwater goods. Pre-application advice is available for a fee and, in our experience, is worth it for anything in a conservation area or on the river.
Fees and timelines
Richmond upon Thames 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
- Richmond Council: House Extensions and External Alterations SPD (May 2015)
- Richmond Council: Local Plan 2024 to 2039 (adopted October 2025)
- Richmond Council: Supplementary planning documents and guidance
- Richmond Council: Conservation areas frequently asked questions
- 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.
- London Borough of Richmond upon Thames: planning: the council's own constraints map, validation checklist and pre-application service.
