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 Reigate and Banstead
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 Reigate and Banstead are listed below, taken from our Reigate and Banstead area page. Each one is a reason to confirm the address on Reigate and Banstead's constraints map before relying on permitted development.
- Green Belt. Most of the borough outside Reigate, Redhill, Banstead and Horley is Green Belt, including land around Kingswood, Chipstead, Merstham, Salfords and the North Downs. Where planning permission is needed, extensions to houses in the Green Belt must not be disproportionate to the original dwelling, and outbuildings face a stricter test on size, siting and effect on openness. Check the council's constraints map to see whether your plot is inside the boundary. Source
- Surrey Hills National Landscape. The North Downs above Reigate, including Reigate Hill, Colley Hill and the scarp towards Merstham, fall within the Surrey Hills National Landscape (formerly the Surrey Hills Area of Outstanding Natural Beauty). Officers give great weight to landscape and scenic beauty, so extensions and outbuildings there are judged on scale, materials and visibility as well as on Green Belt policy. Source
- Conservation areas. Reigate town centre, Banstead, Chipstead, Kingswood and Merstham are among the borough's conservation areas. Roof extensions are not permitted development inside them, and officers apply the character appraisal to extensions, dormers and boundary treatments. Check the council's constraints map for the exact boundaries before relying on permitted development. Source
- River Mole and Redhill Brook flood risk. The River Mole and its tributaries run through Horley, Salfords and Sidlow, and the Redhill Brook drains Redhill and Earlswood towards the Mole. Land alongside them sits in Flood Zones 2 and 3, so ground-floor extensions, basements and outbuildings there may need a flood risk statement with the application. Source
- Listed buildings. Reigate town centre, Banstead, Chipstead, Merstham and the villages contain many listed houses, cottages and churches. Listed building consent is needed for almost any alteration, internal or external. Source
What Reigate and Banstead planning officers look for
Reigate and Banstead Borough Council officers assess householder applications against the Core Strategy, the Development Management Plan and the council's supplementary guidance on residential extensions. On the 1930s semis in Nork, Banstead, Earlswood and Merstham they tend to look for two-storey side extensions set back from the front wall and below the main ridge, a gap kept to the side boundary so the pair does not read as a terrace, and rear extensions that pass the 45-degree test to the neighbour's nearest habitable window. On Reigate Hill and in Kingswood and Chipstead plot coverage, tree protection and the spacious, wooded character of the road carry more weight, and inside the Surrey Hills the landscape impact is tested too. In the Green Belt officers usually measure the extension against the original dwelling by floorspace or volume and treat outbuildings more strictly. Common refusal reasons are full-width box dormers, side extensions that create a terracing effect, and disproportionate additions in the Green Belt. The council offers a paid pre-application service. Decisions can run past the statutory 8 weeks; allow 8–12 weeks.
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.
