How Big Can You Build Without Planning Permission? | Checkatrade
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How big can you build without planning permission?

In the UK, permitted development rights allow you to make some changes to your home without needing to seek planning permission. And that includes building certain kinds of extensions!

If you’re wondering how big you can build without planning permission, that depends on the kind of extension you’re hoping to build, and whether your home is detached, semi-detached or terraced.

Just bear in mind:

  • You can’t extend a house without planning permission if it’s been extended before (since 1948).
  • If your property has been converted into a house in the past or undergone a change of use, permitted development rights might not apply.
  • If your home is listed or in a conservation area, it will have limited or revoked permitted development rights.
  • Permitted development rights won’t apply to flats, maisonettes or other kinds of buildings.

Before building without planning permission, we’d recommend contacting your local planning authority to check planning requirements, just in case!

Rear extensions

  • Single-storey extensions can go as far as 4m for a detached house or 3m for semi-detached and terraced houses.
  • If you get prior approval, this can be extended as far as 8m for detached houses and 6m for others.
  • Double-storey extensions can go as far as 3m from the original house as long as they remain more than 7m from the rear wall.
  • They can’t use more than half of the land surrounding the original building.
  • They can’t be taller than the tallest part of the original building.

Side extensions

  • Side extensions can only be one storey.
  • They mustn’t be more than 4m high.

Front extensions

  • Front extensions must be single-storey.
  • They mustn’t go further than 3m.
  • They mustn’t be more than half of the width of the original house.
  • You can only build a front extension without planning permission if it doesn’t front onto the road.


  • Porches can be built without planning permission as long as they’re not higher than 3m.
  • The external ground area mustn’t be more than 3m2.
  • They have to be at least 2m away from any boundary next to a highway.

An architect will be able to help you design an extension that falls within your permitted development rights.

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