Do you need planning permission for an extension

Depending on the size, type of house and which elevation you want to extend, small single-story extensions can often be built under permitted development, meaning planning permission is not required. However, this is only providing all the relevant planning and design criteria are met and there are no constraints which limit or remove your permitted development rights.

Large or double-story extensions usually require full planning permission which can be applied for with a householder planning application. Flats and maisonettes do not benefit from permitted development rights so in order to extend planning permission is always required.

Some extensions also require prior approval even though they are considered permitted development. In these cases, work must not start until the local planning authority approves the application for prior approval.

For extensions that are likely to fall within permitted development a lawful development certificate is recommended as this is the only way to get a legal determination that your extension is permitted development. This will likely be required should you wish to sell the property at any stage in future and it protects you from any retrospective planning issues, enforcements or penalties.

Building regulations approval will likely also be required once planning permission is approved, depending on the extent of the works.

If there are any hidden constraints that limit or remove your permitted development rights, full planning permission may be required even if your project complies with all the permitted development criteria.

The following is a brief overview for the planning requirements for each type of extension:

For all extensions

• Only half the area of land around the original house can be covered by extensions or other buildings.
• Extensions cannot be higher than the highest part of the existing roof; or higher at the eaves than the existing eaves.
• Where the extension comes within two metres of the boundary the height at the eaves cannot exceed three metres.
• Extensions cannot be built forward of the principal elevation or, where it fronts a highway, the side elevation.
• The materials used in any exterior work must be of a similar appearance to those on the exterior of the existing house.
• On designated land all side extensions will require householder planning permission.

For side extensions

• Where it would extend beyond the ‘side elevation’ of the original house, the extension:
• 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 designated land all side extensions will require householder planning permission.

For single storey extensions

• 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.
• For extensions of more than one storey
• 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).
• All side extensions of more than one storey will require householder planning permission.

IMPORTANT: These are only a general guide and every planning authority will assess each proposed extension on its own merits. There is no one size fits all or black and white definitive answers with planning permission due to the number of variables such as design, site location and constraints.

If you would like to be sure whether your proposed extension is feasible, requires planning permission or not and the likelihood of the planning authority approving your application contact us to speak with our planning experts today.

Get in touch!