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 Waltham Forest
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 Waltham Forest are listed below, taken from our Waltham Forest area page. Each one is a reason to confirm the address on Waltham Forest's constraints map before relying on permitted development.
- Conservation areas. Waltham Forest's conservation areas include Walthamstow Village, Bushwood in Leytonstone and Highams Park. Roof extensions are not permitted development inside them, and officers apply the character appraisal to rear extensions and dormers. Check the council's constraints map for the exact boundaries. Source
- Article 4 directions. Waltham Forest has used an Article 4 direction to remove permitted development for converting a house into a small house in multiple occupation (C3 to C4) across the borough, and some conservation areas have directions removing permitted development for front alterations and roof works. Check the constraints map before relying on permitted development. Source
- Epping Forest land and Green Belt. Epping Forest land runs down the borough from Chingford through Highams Park to Leyton Flats and Wanstead Flats, and the north of the borough is Green Belt. The Forest is protected open space within the Epping Forest Special Area of Conservation, and houses adjoining it or in the Green Belt face stricter tests on extensions and outbuildings. Source
- Lee Valley flood risk. The western edge of the borough along the River Lea, including Lea Bridge, Blackhorse Lane, the Walthamstow Wetlands edge and Marsh Lane in Leyton, sits in Flood Zones 2 and 3. Ground-floor extensions and basements there may need a flood risk statement with the application. Source
- Listed buildings. Walthamstow Village around St Mary's Church, Vestry House and the Ancient House, Bushwood in Leytonstone and Chingford's old centre contain listed buildings. Listed building consent is needed for almost any alteration, internal or external. Source
What Waltham Forest planning officers look for
Waltham Forest officers assess householder applications against the Local Plan and the council's supplementary guidance on residential extensions and alterations. On the terraces of Walthamstow and Leyton they expect rear extensions to sit within the pattern of the street, single storey at the side return and below the neighbour's first-floor sill, and rear dormers that are set back from the eaves and below the ridge with matching slate or tile. Full-width box dormers, dormers on front roof slopes and roof extensions on unbroken rooflines in Walthamstow Village and Bushwood are the standard refusals. Warner half-houses are assessed as flats, so a loft or rear extension there needs a full planning case and often the agreement of the other half of the pair. Outside conservation areas, rear dormers within 40 m³ on a terraced house are routinely lawful and we secure a Lawful Development Certificate as proof. The council offers paid pre-application advice. Decisions often run past the statutory 8 weeks; allow 10–12 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.
