Planning permission for outbuildings: everything you need to know

Thinking of adding a garden office, gym or annexe to your home? Property expert Michael Holmes gives us the lowdown on planning permission for outbuildings.
- Planning permission
is not required providing use of the building is "incidental to the enjoyment of the main dwelling house" and its design falls within the definition of "permitted development" (see for more details). 

- Permitted development essentially allows home owners to construct an outbuilding in their back garden and sometimes side garden, too, covering up to half of the original garden area, providing it is:
  • ​Less than four metres in height with a pitched roof
  • Less than three metres high with a flat roof
  • No taller than 2.5 metres at eaves height; and
  • No closer than two metres to the boundary. 
- Use of an outbuilding as self-contained accommodation is irrelevant as to whether the development is permitted, but the building cannot be used as an "independent separate dwelling" - in other words, members or dependents and guests of the main household can stay there, but it cannot be let out or sold as a separate dwelling. 

- Planning authorities vary in their approach to annexes and some will try to resist the development even where it constitutes permitted development. In this instance, it can be easier to construct the outbuilding for some other use, such as a home office, and then change the use once the work is complete.

- There are limitations on permitted development rights for outbuildings in National Parks, conservation areas and other designated areas. Planning permission is always required for outbuildings within the cartilage of a listed property.

- Compliance with Building Regulations: if in doubt, always check with your local planning authority. Whether or not planning permission is required, the building will need to comply with the Building Regulations.
- If a planning application is required, it will take 8-10 weeks for a decision, following registration. If the property is an annexe, the planners will usually place a condition on its use to prevent letting out to a third party. 

- Permitted development work can commence without notice, unless Building Regulations or a Party Wall agreement is required because the building work is on or near the boundary with the neighbours.
- A planning application for a garden outbuilding currently costs £172 in England. Building Regulations consent will cost from £200-£300 upwards, depending on scale. 
- "Material considerations" will be taken into account to determine the impact on neighbouring properties and on the setting. 

- Taller structures that overlook or overshadow neighbours’ properties are unlikely to be acceptable. Single-storey designs are unlikely to be an issue, providing the windows cannot overlook neighbouring properties. 

- Vehicular access down the side of a property to reach an annexe can be an issue if it impacts on neighbours.

Apply for planning permission online

With thanks to Michael Holmes, spokesman for The London Homebuilding & Renovating Show (25-27 September, ExCeL London).

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