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 Croydon
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 Croydon are listed below, taken from our Croydon area page. Each one is a reason to confirm the address on Croydon's constraints map before relying on permitted development.
- Conservation areas and Local Areas of Special Character. Croydon has numerous conservation areas, including the Webb Estate, Chatsworth Road, Church Street, Norwood Grove and Bradmore Green, plus Local Areas of Special Character identified in the Local Plan. Roof extensions are not permitted development in conservation areas and design scrutiny is tighter in both. Source
- Green Belt and Metropolitan Open Land. The southern third of the borough, including Coulsdon, Kenley, Sanderstead, Selsdon and Addington, contains extensive Green Belt and Metropolitan Open Land. Extensions must not be disproportionate to the original house and outbuildings face a strict test. Source
- Article 4 directions. Croydon has Article 4 directions in several conservation areas, including the Webb Estate, removing permitted development for front alterations, boundary treatments and some roof works. Directions may also affect office-to-residential conversions in the town centre. Check the council's constraints map before relying on PD or prior approval. Source
- Flood risk – Wandle and surface water. The River Wandle rises in Croydon and parts of Waddon, Beddington borders and the town centre carry fluvial or surface-water flood risk. Some valley streets in Purley and Kenley also flood after heavy rain. Ground-floor extensions here may need a drainage or flood statement. Source
What Croydon planning officers look for
Since the Suburban Design Guide was revoked, Croydon officers have become more protective of suburban character. Refusals most often cite two-storey side extensions without a set-back that create a terracing effect, rear extensions that breach the 45-degree line, oversized rear dormers that wrap the hip, and any loss of gaps between houses in Local Areas of Special Character. Hip-to-gable lofts on ordinary semis are generally accepted. Pre-application advice is available for a fee, and decision times often exceed the statutory 8 weeks; allow 10–14 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.
