Planning permission for an extension
Many single-storey extensions fall under permitted development, but the depth, height and coverage limits are strict, and get stricter near boundaries or on designated land.
An extension is one of the most common ways to add space, and one of the most common places people get the planning route wrong. Whether you need a full application comes down to the size and position of the extension, the type of house and where it is.
- Single-storey rear extensions up to 4m (detached) or 3m (other houses) deep, or up to 8m / 6m under the Larger Home Extension prior-approval process
- Maximum 4m height for single-storey; eaves capped at 3m within 2m of a boundary
- No more than half the land around the original house covered by extensions and outbuildings
- Materials similar in appearance to the existing house; no forward-of-the-principal-elevation builds
- Any extension beyond the permitted development limits above
- All multi-storey side extensions, and rear extensions over 3m deep at first-floor level
- Homes in conservation areas, National Parks or AONBs, and flats or maisonettes
- Properties where permitted development rights have been removed by an Article 4 direction or condition
Don't forget building regs
Almost every extension needs building regulations approval: foundations, structure, insulation, drainage and fire safety are all assessed. We prepare that package separately from the planning drawings.
Checking the right route is one of the very first things we do. We assess your extension against permitted development and local rules, tell you whether you need a full application or a Certificate of Lawful Development, and prepare the drawings either way. See real schemes on our house extensions page, or get a fixed price from the instant quote tool.
Frequently asked
How deep can an extension be without planning permission?
Under permitted development a single-storey rear extension can be up to 4m deep on a detached house or 3m on any other house. Deeper extensions, up to 8m or 6m, are possible through the Larger Home Extension prior-approval process, provided the property is not on designated land. We confirm the exact limit for your home.
Do I need planning permission for a two-storey extension?
Often, yes. Two-storey and multi-storey extensions have tighter limits. They cannot extend more than 3m to the rear, must sit 7m from the rear boundary, and all multi-storey side extensions need permission. We check yours and prepare the application if needed.
Not sure where your project stands?
Checking whether you need planning permission is one of the first things we do: on the house, before any drawings. Tell us about your project and we'll confirm the route.