Can I detach a semi and extend it? - Build It (2024)

Hi Bighouse,

While this is an unusual project it’s not unheard of for semi-detached properties to be detached from one another. Exactly how you approach it will depend on the plot and ownership situation, among other things – for example, you might completely knock down one of the pair and rebuild elsewhere on the plot.

The best place to start may well be to speak to your local authority’s planning department and gauge their reaction. Most councils offer a pre-application advice service (these are sometimes free but may be chargeable). If you feel under-prepared for this you could take advice from an architect or planning consultant first.

One concern from a planning perspective is likely to be whether your project materially alters the streetscene (eg if this is a street of similar semi detached houses with an overriding style; or . If you were replacing like-with-like in terms of size, ridge heights etc then you’d probably have the best chance of gaining approval.

Where you intend to increase the size by 45m2, this could be an issue. That said, it’s possible that the existing semi might be extendable to this size anyway either via permitted development or a separate planning application (in which case you could use this fact to argue in favour of a full redevelopment).

There are some practical considerations, too – detaching the houses will involve significant works to support the other house during the works and then consolidate its integrity for future occupation. This is likely to involve Party Wall agreements etc. It would also mean refinishing a new wall on the other house to a satisfactory standard. This will obviously be much more problematic if you don’t own both properties.

I’d recommend that you get in touch with a planning consultant or your local planning office to try to discuss the options with specific consideration for your plot.

Good luck!

Chris Bates (Deputy Editor & Online Editor, Build It magazine)

26 November 2014