Extension architect

Good news – you don’t need planning permission for an extension, subject to some exceptions and rules, outlined below. Many rear extensions benefit from permitted development rights, which means that you do not need planning permission. However, you should check that your property is not exempt (see below).


Extension pictured above by Oliver, architect from Wandsworth, London. Click here to see more and shortlist their studio for your home project.


The notes below are intended as a brief summary and should not be taken as design guidance. We strongly recommend you read the official guidance in full before proceeding (read it here):


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Extension size

It’s possible to build a single storey extension up to six metres without planning permission (or eight metres if your house is detached). If the house has previously been extended already (since 1948), this will eat into your six or eight metre allowance. Please note that for these larger extensions (beyond three and four metres respectively) you will need to give notification under the Neighbour Consultation Scheme.


Property type

Permitted development rights only apply to houses, not flats or maisonettes. Also, be aware that if your property has undergone a change of use or been converted into a house in the past, it may not benefit from permitted development rights.


Permitted development – Conservation Areas, Listed Buildings etc.

Or other ‘protected’ areas, including Conservation Areas, National Parks, areas of Outstanding Natural Beauty, the Norfolk or Suffolk Broads or a World Heritage Sites etc, your permitted development rights might have been removed. Check if there is an Article 4 Direction for your property.

Potentially it may only be the case that your permitted development rights have been restricted, meaning you cannot:

  • Build more than one storey.
  • Build a side extension.
  • Or clad the exterior.


Permitted development rules for single storey rear extensions

  • Materials to be similar to the existing house.
  • No verandas, balconies or raised platforms.
  • Must not be taller than the existing house.
  • The extension(s) should not take up more than 50% of the garden/outdoor space.
  • Can’t be more than four metres high. If the extension is within two metres of the properties boundary, it can’t be more than three metres high.


Permitted development rules for double storey rear extensions

The same rules as single storey extensions apply, except for height restrictions. In the case of a double storey extension:


  • The eaves and pitch heights must be no higher than those of the existing house. However, if the building is within two metres of a boundary, the overall maximum eaves height is restricted to 3m. The roof pitch should match the existing house as much as reasonable practicable.
  • Two storey extensions to the side or front of the original house are not permitted development.
  • Any upper floor window in a side elevation must be obscured glazing and non-opening (unless its more than 1.7m from floor level internally).


Can you extend at the front of the house under permitted development?

Front extensions are not allowed under permitted development rules, but you can still apply for planning permission.


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