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 Bexley
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 Bexley are listed below, taken from our Bexley area page. Each one is a reason to confirm the address on Bexley's constraints map before relying on permitted development.
- Conservation areas. Bexley has a modest number of conservation areas, including Bexley Village (Old Bexley), and several historic centres and estates. Roof extensions lose permitted development rights inside them and side extensions face closer design scrutiny. Check the council's constraints map for your address. Source
- Thames and Cray flood risk. Erith, Belvedere, Thamesmead, Slade Green and the Crayford Marshes lie in Flood Zones 2 and 3 behind the Thames defences; the River Cray and Shuttle also carry fluvial flood risk. Ground-floor extensions in these zones may need a short flood risk assessment. Source
- Green Belt and Metropolitan Open Land. Foots Cray Meadows, the Cray valley, Lesnes Abbey Woods and Crayford Marshes include Green Belt and Metropolitan Open Land. Extensions and outbuildings here must be proportionate and are judged more strictly. Source
- Article 4 directions. We are not aware of a borough-wide Article 4 direction removing householder permitted development in Bexley, but directions may exist for specific conservation areas or for houses in multiple occupation. Confirm on the council's constraints map before building under PD. Source
What Bexley planning officers look for
Bexley is, in our experience, a relatively straightforward authority for suburban householder work. Officers focus on the 45-degree test from neighbouring windows, the depth of single-storey rear extensions beyond the neighbour, and whether two-storey side extensions are set back from the front wall so that pairs of semis do not merge into a terrace. Front dormers and flat-roofed dormers that wrap the hip are the usual loft refusals. The council generally offers a paid pre-application service. Decision times are usually close to the statutory 8 weeks, though a formal extension of time is not unusual.
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.
