Side extensions in Bromley depend on the house. Typical homes here: 1930s semi-detached houses in Orpington, West Wickham, Hayes, Bromley Common and Mottingham; Edwardian and interwar detached houses in Bickley, Chislehurst, Petts Wood and Sundridge Park. Designations to check first: Conservation areas; Green Belt and Metropolitan Open Land; Article 4 directions. Applications are decided by London Borough of Bromley and the Bromley Local Plan (2019).
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 Bromley
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 Bromley are listed below, taken from our Bromley area page. Each one is a reason to confirm the address on Bromley's constraints map before relying on permitted development.
- Conservation areas. Bromley has numerous conservation areas, including Chislehurst, Petts Wood, Bickley Park, Beckenham Place, Sundridge Park, Keston and several around Bromley town centre. Source
- Green Belt and Metropolitan Open Land. Roughly half of the borough is Green Belt or Metropolitan Open Land, taking in Keston, Downe, Cudham, Biggin Hill, Chelsfield and Pratts Bottom. Source
- Article 4 directions. Several Bromley conservation areas, including parts of Chislehurst and Petts Wood, have Article 4 directions removing permitted development for front-facing alterations, boundary treatments or roof works. Source
- Flood risk: Ravensbourne, Cray and Beck. The River Ravensbourne, Cray, Beck and Pool River corridors through Beckenham, Shortlands, Bromley and St Mary Cray carry fluvial flood risk. Source
What Bromley planning officers look for
Refusals most often cite two-storey side extensions that close the gap between houses or lack a set-back, rear extensions that breach the 45-degree line to a neighbour, and roof extensions in conservation areas or Areas of Special Residential Character. Rear dormers on ordinary semis outside protected areas are usually accepted if they sit below the ridge and inside the roof slope. The council generally offers a paid pre-application service; decisions often run beyond 8 weeks, so allow 10–14 weeks.
Fees and timelines
Bromley decides a householder application or a Lawful Development Certificate within 8 weeks of validation. The council fee is £528 for a householder application and £264 for a Lawful Development Certificate (England, from 1 April 2025; verify before applying).
Our own fee is fixed once quoted. The quote tool gives an indicative figure in minutes and a written quote follows within 24 hours.
Primary sources
- The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2: the permitted development limits quoted above.
- Planning Portal: do you need permission: the national guidance and the application service every council accepts.
- London Borough of Bromley: planning: the council's own constraints map, validation checklist and pre-application service.
