Do I need planning permission for a house extension?

Not every home extension needs planning permission, although it’s probably worth obtaining a Certificate of Lawful Development from the local planning authority for your own peace of mind even if your project does appear to be permitted development. The law can be complicated so expert advice should be sought if in doubt.

What is permitted development?

You can carry out certain types of construction work without needing to apply for planning permission. These are called “permitted development rights”. The permitted development rights which apply to many common projects for houses do not apply to flats, maisonettes or other buildings, and commercial properties have different permitted development rights to dwellings. In some areas of the country, known generally as Article 2(3) designated areas, permitted development rights are more restricted and planning consent will be required. For example:

  • a Conservation Area
  • a National Park
  • an Area of Outstanding Natural Beauty
  • a World Heritage Site or
  • the Norfolk or Suffolk Broads

There are different requirements if the property is a listed building. Your solicitor may have advised you when you bought your home that it is covered by an ‘Article 4’ direction. These are made when the character of an area of acknowledged importance would be threatened, and are most common in conservation areas. Being affected by an Article 4 direction means that you have to submit a planning application for work which normally does not need one.

Do I need planning permission for a single-storey rear extension?

The quick answer is ‘probably not’, although certain criteria need to be observed including:

  • Single-storey rear extensions cannot extend beyond the rear wall of the original house* by more than four metres if a detached house; or more than three metres for any other house.
  • Where not on Article 2(3) designated land or a Site of Special Scientific Interest; and subject to ‘prior approval’, the limit for single-storey rear extensions is increased to eight metres if a detached house; or six metres for any other house. This requires that the relevant Local Planning Authority is informed of the proposed work via a prior approval application.
  • Single-storey rear extensions cannot exceed four metres in height.

* The term ‘original house’ means the house as it was first built or as it stood on 1st July 1948 (if it was built before that date).

Do I need planning permission for a two-storey rear extension?

Not necessarily.

  • Extensions of more than one storey must not extend beyond the rear wall of the original house by more than three metres or be within seven metres of any boundary opposite the rear wall of the house.
  • Roof pitch must match existing house as far as practicable (note that this also applies to any upper storey built on an existing extension).
  • Any upper-floor window located in a ‘side elevation’ must be obscure-glazed; and non-opening (unless the openable part is more than 1.7 metres above the floor).

On Article 2(3) designated land all rear extensions of more than one storey will require householder planning permission.

Do I need planning permission for a single-storey side extension?

It depends. A side extension that is permitted development:

  • Cannot exceed four metres in height.
  • Can only be a single storey.
  • Can only be up-to half the width of the original house.

On Article 2(3) designated land all side extensions will require householder planning permission. A ‘wraparound’ single-storey extension (ie to the side/rear) will always require planning permission.

Do I need planning permission for a two-storey side extension?

Yes. All side extensions of more than one storey will require householder planning permission.

Does the 45° Rule apply to permitted development projects?

The short answer is ‘no’. Any project that needs planning permission will be evaluated by the local planning authority to check that it doesn’t violate neighbours’ rights under the so-called 45° Rule, but this doesn’t apply to permitted development. Although this might sound like good news, caution is needed because if you have not considered your neighbour’s right to light they may have a case against you for compensation or might even successfully demand change to the proposed (or constructed) building.

Does the right to light apply to permitted development projects?

Yes, if your new extension breaches your neighbour’s right to light, they are entitled to take action against you – although this would be rare, and we have certainly never known it occurring with any of our clients. A right to light is protected in England and Wales under common law, adverse possession or by the Prescription Act 1832 and is a completely separate matter from planning and therefore a development might in theory have planning permission but still fall foul of rights of light. However, an extension that complies with the 45° Rule would be unlikely to breach a right to light.

Can I add an extra storey to my house by extending upwards?

From 31st August 2020, building an additional storey on to your house is considered to be permitted development subject to the following limits and conditions although you will need to make an application for the Local Authority’s prior approval. If the planning authority is not satisfied with any of the following, prior approval will not be granted and a full planning application will be necessary: The current house:

  • Is not a building containing one or more flats, or a flat contained within such a building.
  • Was constructed between 1st July 1948 and 5th March 2018.
  • Has not already had additional storeys added to it.
  • Is not on Article 2(3) land* or a site of special scientific interest.
  • Was not changed to be used as a house (from a previous non-residential use) under permitted development rights.

Limitations on the proposed development:

  • Number of additional storeys:
    • One storey can be added to a single storey house.
    • Two storeys can be added if the house has more than one storey.
  • Height increases:
    • The house cannot exceed 18 metres in total height.
    • Each added storey cannot add more than 3.5 metres to the total height.
    • If not detached (e.g. terrace or semi) the total height cannot be more than 3.5 metres higher than the next highest building that the house is attached to, adjoins, or is in the same row as.
  • The additional storeys must be constructed on the principal part of the house (ie the main part of the house excluding any front, side or rear extension of a lower height (regardless of these being part of the original house or subsequent additions).
  • The additional storeys must not exceed three metres in height or the height of any existing storey in the principal part* of the house (measured internally from floor to ceiling).
  • Engineering operations must only include works within the existing curtilage of the house to strengthen existing walls and foundations.
  • The materials used must be of a similar appearance to those used in the construction of the exterior of the current house.
  • Windows must not be placed in any wall or roof slope forming a side elevation of the house.

Following completion of development:

  • The house must remain in use as a domestic residential property.
  • No visible support structures must remain on or attached to the exterior of the house.
  • The roof pitch of the principal part* of the house must be the same as it was prior to the development.

Sue Humphrey, Director, Ecclesall Design

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