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 Guildford
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 Guildford are listed below, taken from our Guildford area page. Each one is a reason to confirm the address on Guildford's constraints map before relying on permitted development.
- Green Belt. Most of the borough outside Guildford town and the larger villages is Green Belt, including land around Shalford, Send, Ripley, East Horsley and Effingham. 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 Surrey Hills National Landscape (formerly the Surrey Hills Area of Outstanding Natural Beauty) covers the downs and wooded slopes south and east of the town, including land around Shalford, the Horsleys and Effingham. 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 and Article 4 directions. Guildford town centre, Charlotteville and Onslow Village are conservation areas, and many of the villages, including Shalford, Ripley, Send, East Horsley and Effingham, have designated centres. Roof extensions are not permitted development inside them. Onslow Village is also understood to have an Article 4 direction removing further permitted development rights on the estate. Check the council's constraints map for the exact boundaries and any directions before relying on permitted development. Source
- Thames Basin Heaths Special Protection Area. The heathland around Ash and the north-west of the borough forms part of the Thames Basin Heaths Special Protection Area. New dwellings within 400 m of the SPA are normally resisted and those within 5 km usually have to contribute to mitigation. Extensions, lofts and garden rooms to an existing house are usually unaffected, but a new dwelling, an annexe or a flat conversion near Ash will need to address the policy. Source
- River Wey flood risk. The River Wey and the Wey Navigation run through Guildford town centre and on through Shalford, Send and Ripley, and land alongside them sits in Flood Zones 2 and 3. Ground-floor extensions, basements and outbuildings there may need a flood risk statement with the application. Source
- Listed buildings. Guildford town centre, Shalford, Ripley, Send, the Horsleys and Effingham contain many listed houses, cottages and churches. Listed building consent is needed for almost any alteration, internal or external. Source
What Guildford planning officers look for
Guildford Borough Council officers assess householder applications against the Local Plan: Strategy and Sites, the Development Management Policies and the council's supplementary guidance on residential extensions. On the 1930s semis in Stoughton, Burpham and Merrow 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. In Onslow Village and Charlotteville the character appraisal drives decisions on materials, roof form and frontages. In the Green Belt and the Surrey Hills 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 on village plots. 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.
