House extensions in Hillingdon

Hillingdon's rear extension limits

• Terraced and semi-detached houses: up to 3.3 metres deep on plots 5 metres wide or less, or 3.6 metres on wider plots.
• Detached houses on plots of 5 metres or more: up to 4 metres.
• Height: flat roofs up to 3 metres; pitched or sloping roofs up to 3.4 metres, measured from ground level.
• Extending an existing extension, or adding a conservatory to one, won't normally be supported.

Since 22 September 2014, a borough-wide Article 4 direction has removed permitted development rights for rear extensions projecting more than 4 metres, so deeper extensions need a full application judged against these limits.

Side and two-storey extensions

Side extensions should be less than half the width of the original house. Two-storey side extensions should be set in at least 1 metre from the boundary (1.5 metres on the Copse Wood and Gatehill estates) and set back 1 metre from the front. Two-storey extensions must stay outside a 45-degree line from neighbours' nearest habitable-room windows and avoid windows that overlook other houses within 21 metres. Full-width two-storey rear extensions are not acceptable in conservation areas, where flat-roofed single-storey extensions are expected to have a parapet. Balconies or access to flat roofs that cause a loss of privacy won't be permitted.