Guides · 6 min
Do I need planning permission for a rear extension?
The simple rules for a single-storey extension at the back of a house in England.
Often yes, sometimes no
A rear extension is the job people ask about most. On many houses you can build a single-storey one without a full planning application, if you stay inside national size limits and nobody has taken those rights away.
For a house that is not on special land, the usual depth is up to 3 metres for an attached house and 4 metres for a detached house, measured from the original back wall. A larger scheme, up to 6 metres attached or 8 metres detached, can use a lighter prior-approval check instead of a full application. The height is limited, often to 4 metres, and there are rules about the eaves and the boundary.
When you do need an application
You usually need a full application if the extension is two storeys, if it sticks out past a side wall, if the house is a flat, or if you are in a conservation area, on a listed building, or on land where the rights have been removed.
Earlier rear extensions use up the allowance. A house that already has a big back addition may have little room left.
Check with your council. Rules change, and every house is different.
Questions
Is 3 metres always allowed?
No. That is a common national limit for an attached house, not a promise. The rights must still be there, and other limits apply.
Does a rear extension need building regulations?
Usually yes, even when it does not need planning permission. Building regulations are about safety, not about whether the look is allowed.
Check with your council. Rules change, and every house is different.