An extension to your house will fall under 'permitted development' rules (which means you won’t need to get planning permission) if your proposed extension conforms to the permitted development rules below.
(N.B. Different rules apply if you’re in a conservation area or if you’re planning to extend a listed building (see below). And they only apply to houses - not to flats and maisonettes.)
Extension permitted development rules
- It takes up not more than half the area of land around the 'original house' (you may well see this land, within the boundary of your property, referred to by the legal term 'curtilage'). The 'original house' is either how it was in 1948 (it may have had previous extensions before then) or how it was newly built (after 1948).
- It isn’t forward (in front) of the principal elevation (front of your house) or side elevation (side of the house) onto a highway (this refers to a way that members of the public are entitled to pass and repass over).
- It isn’t higher than the highest part of your roof.
Single storey extensions
- It mustn’t be higher than four metres
- It mustn’t extend beyond the back wall of the original house by more than eight metres for a detached house, or more than six metres for any other house
More than one storey
- It mustn’t extend beyond the rear wall of the original house by more than three metres
- Two-storey extensions can’t be closer than seven metres to the rear boundary of your property.
- Single storey with a maximum height of four metres and width no more than half that of the original house.
- You have to use materials that are similar in appearance to the existing house
- Your extension won’t include verandas, balconies or raised platforms
- Any side-facing windows on the upper floor will be obscure-glazed and any opening will be 1.7m above the floor.
Listed building extensions
You’ll need planning permission and most likely listed building consent from your local council planning department, so it’s best to speak to them. Historic England have advice on work to listed buildings in England, as a starting point.
Extensions to homes in conservation areas
You’ll also need planning permission for extensions in conservation areas. Contact your council’s planning department for advice. Again, Historic England is a good place to start for information on historic buildings.
Visit this government page for full details or speak to the planning department at your local council.