A loft conversion for your house is considered to be permitted development, not requiring an application for planning permission, subject to the following limits and conditions: A volume allowance of 40 cubic metres additional roof space for terraced houses* If any of the conditions below are not met you will require planning permission.
The loft conversion does not extend beyond the plane of the existing roof slope.
No part of the loft conversion is higher than the existing roof.
No verandas, balconies or raised platforms are to be added.
Your property is not in an area of outstanding beauty or a conservation area.
The loft conversion (except hip to gable) is set back 20cm or more from the original eaves.
The extension does not overhang your property
For the full list of regulations for planning permission, check your local council's planning portal