Guides · 5 min
Two-storey extensions
A two-storey extension almost always needs permission, and the side gap matters.
Assume an application
Two-storey rear or side extensions are not the simple national right that covers a modest single-storey rear extension. Plan on a full application.
Councils look at whether the new part is smaller than the main house, the gap to the boundary, and the neighbour’s windows. A first-floor wall on the boundary is a common reason for a no.
The version that does better
Set the first floor in from the side. Keep the roof lower than the main ridge. Use matching materials. Do not unbalance a pair of semis by making one half much wider.
If the nearby yeses are all single storey, treat a two-storey plan as the less certain one.
Check with your council. Rules change, and every house is different.
Questions
Is there a national two-storey permitted development right?
There is a limited one for some rear extensions, with tight limits on depth and distance to the boundary. Many real two-storey plans fail those limits and need an application.
What is a metre gap?
Some councils, including Bromley, often ask for about a metre between a two-storey side wall and the boundary. It is a local habit, so check the policy in force.
Check with your council. Rules change, and every house is different.