Make sure you understand whether your building extension requires planning permission before proceeding with the build to avoid costly mistakes.

Building an extension on your home is an affordable way of gaining valuable new living space in the house you love.

Changes to the law now mean that most extensions are classed as permitted developments and so do not require planning permission. The newly relaxed laws were first implemented as temporary changes in 2014, but from May 2019 onward they became permanent.

There is, however, a strict set of criteria that must be met to make an extension a permitted development and making changes to the house without first obtaining planning permission can be a very costly mistake.

If you’re unsure about whether your project requires planning permission or meets relevant building regulations, then consult an expert before proceeding.

Planning permission exemption criteria for extensions

An extension to your home does not require planning permission providing it meets the following key conditions according to the Planning Portal.

  • No more than half the area of land around the “original house”* would be covered by additions or other buildings. The term “original house” means the house as it was first built or as it stood on 1 July 1948.
  • No extension forward of the principal elevation or side elevation fronting a highway.
  • No extension to be higher than the highest part of the roof.
  • Single-storey rear extensions must not extend beyond the rear wall of the original house* by more than eight metres if a detached house; or more than six metres for any other house.
  • Maximum height of a single-storey rear extension of four metres.
  • Extensions of more than one storey must not extend beyond the rear wall of the original house* by more than three metres.
  • Maximum eaves height of an extension within two metres of the boundary of three metres.
  • Maximum eaves and ridge height of extension no higher than the existing house.
  • Two-storey extensions no closer than seven metres to rear boundary.
  • The roof pitch of extensions higher than one storey to match the existing house.
  • Materials to be similar in appearance to the existing house.
  • No verandas, balconies or raised platforms.
  • Side extensions to be single-storey with a maximum height of four metres and width no more than half that of the original house.
  • Upper-floor, side-facing windows to be obscure-glazed; any opening to be 1.7m above the floor.

These conditions only apply to houses, the rules differ for flats, maisonettes, converted houses and properties on designated land.

The full list of conditions can be found on the Planning Portal website.

Whether or not your extension requires planning permission, it will still need to comply with all relevant building regulations. Building regulations ensure that all new structures are safe and energy-efficient. Find out more about building regulations.

Designing a house extension

Designing and building a house extension is a job best left to the professionals as there are lots of factors to consider and boxes to tick to ensure that the structure is safe, durable, long-lasting and energy-efficient. There are also countless rules, regulations and laws that must be taken into consideration to ensure that your new extension is fully compliant with the law. At MDA Architectural Services, we provide a full and comprehensive range of architectural design services in Bolton, Greater Manchester and nearby areas to help you turn your concept into a reality. We will help you to ensure that all your extension plans are fully compliant with building control and building regulations and help you to obtain any planning permission necessary