Many rear extensions can be built without planning permission under permitted development rights. Here's exactly when you need permission and when you don't.
Under permitted development, you can extend a detached house by up to 4 metres to the rear, or a terraced or semi-detached house by up to 3 metres, without planning permission — provided the extension doesn't exceed the original roof height and meets several other criteria.
Under the larger home extension scheme (also called prior approval), you can extend a detached house by up to 8 metres or other houses by up to 6 metres, subject to a prior approval process with your council. Neighbours are consulted and can object, but the bar for refusal is lower than a full application.
You'll always need full planning permission if: the house is a listed building; the property is in a conservation area and the extension would be visible from a highway; the extension would cover more than 50% of the curtilage; or permitted development rights have been removed by a condition on the original planning permission.
Apply for a Lawful Development Certificate (LDC) from your council. This confirms in writing that your proposed works are lawful under permitted development. It costs around £103 and is well worth having before you start — it protects you if the council later queries your extension.
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