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's constraints map before relying on permitted development.
- Conservation areas. Richmond has more than 70 conservation areas, covering a large share of the borough's housing. Roof extensions, cladding and side extensions in these areas need planning permission rather than permitted development, and the council publishes character appraisals that officers use to judge design. Check the constraints map for your address before assuming PD applies. Source
- Article 4 directions. Many Richmond conservation areas carry Article 4 directions removing permitted development for front elevations, windows, porches, boundary walls and hardstandings. The exact rights removed differ from area to area, so we check the schedule for your street before recommending a route. Source
- Thames flood zones. Low-lying land at Barnes, Mortlake, Kew, Twickenham riverside, Teddington and Hampton falls within Flood Zones 2 and 3. Basements and new ground-floor habitable rooms may need a flood risk assessment, and the Thames Policy Area adds design expectations for riverside sites. 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. Houses backing onto them are judged on their effect on openness and setting, and outbuildings near the boundary attract extra scrutiny.
- Listed buildings. The borough has a high number of listed buildings, particularly around Richmond Green, Richmond Hill, Petersham, Twickenham riverside and Hampton. Almost any external or internal alteration to a listed house needs listed building consent in addition to planning permission.
What Richmond upon Thames planning officers look for
Richmond is one of the more design-led London planning authorities and its officers apply the House Extensions SPD closely. 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
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.
