Extending or altering existing premises

You will always need to apply for planning permission to extend shops or office premises. However, minor extensions to industrial buildings, including putting up additional buildings within the curtilage, may not require planning permission. 

If you are extending or altering a listed building or a building in a conservation area, you may require planning permission as well as listed building and conservation area consent before you proceed with any works.

Factory or warehouse extensions

Planning permission will not normally be required if your extension is:

• Less than 1,000 square metres of floor space, and
• Less than 25 per cent of the volume of the original building, and
• Below the height of the original building

The building must be related to the current use of the building or the provision of staff facilities.

Planning permission will be required if the extension:

• Materially affects the external appearance of the building, or
• Comes within five metres of the boundary of the site, or
• Reduces the amount of space available for parking or turning vehicles

Original building

Building volume is calculated from external measurements – use the Planning Portal's Volume Calculator tool. 'Original' means as first built, or as the building stood on 1 July 1948, if built before then. The extension volume allowance is once and for all; any previous enlargement of the building counts against these freedoms.