# House extensions in Hillingdon

Canonical URL: https://mirion.uk/areas/hillingdon/extensions/

> Rear, side and two-storey extensions in Hillingdon under policy DMHD 1: plot-width depth limits, heights, set-backs and the borough's 4-metre Article 4 rule.

We build rear, side and two-storey extensions in Ruislip, Eastcote, Ickenham and Northwood, sized from the start to Hillingdon's policy DMHD 1.

### 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.

Hillingdon extensions: common questions

Does plot width affect extension depth in Hillingdon?

Yes. For terraced and semi-detached houses, policy DMHD 1 allows 3.3 metres on plots up to 5 metres wide and 3.6 metres on wider plots.

Can I extend an existing extension in Hillingdon?

Usually not. Hillingdon's Local Plan says proposals to extend existing extensions, including adding conservatories to them, will not be supported.