Find out when a side extension in London may fall under permitted development, when full planning permission is required, and what site-specific constraints affect the outcome.
Side extensions are among the most complex permitted development cases in London. The rules on width, height, and proximity to the original house create a tight envelope, and many side extensions end up needing full planning permission — especially on corner plots or in conservation areas.
These are the common features that keep a project on the simpler route.
These are the usual triggers that push a scheme beyond straightforward PD rights.
The tool is designed to answer the first question most homeowners have: is this worth pursuing, and what is most likely to block it?
CanUBuild checks whether your address sits in a conservation area, listed building curtilage, Article 4 area, or flood risk zone before you commit to the project.
The side extension workflow captures the dimensions and positioning that determine whether the scheme fits within permitted development or needs a full application.
You also see nearby planning decisions so you can assess how your local planning authority has treated similar side extension proposals.
Sometimes. A single-storey side extension can fall within permitted development if it meets the width, height, and other conditions set out in the rules. However, many properties in London — particularly in conservation areas or covered by Article 4 directions — do not benefit from these rights.
Under general permitted development rules, a side extension must not exceed half the width of the original house. This is calculated from the original building footprint, not the plot boundary.
Yes. In conservation areas, permitted development rights for side extensions are often removed, meaning full planning permission is required. The design will also need to respond to local character, materials, and the impact on the streetscene.
Yes. Corner plots often have two road frontages, which means that what appears to be a side wall can face a highway. This usually increases scrutiny of the design and may affect whether permitted development applies.
Search for the address, choose your project type, and get a planning feasibility answer based on permitted development rules, constraints, and local precedent data.