While the double-storey extension options are tighter than a single-storey extension, planning permission is not always necessary.
PERMITTED DEVELOPMENT RIGHTS
In order to build a double-storey house extension, you have to stay within the limitations stated below:
Area: the area of extensions must be less than 50% of the totally free area around the house
Height: for 2 storey extensions, the height must not exceed the height of the existing house eaves. Only single-storey extensions are allowed under permitted development if the distance to the boundary is less than 2m,
Balconies and terraces: they are never allowed within permitted development rights
Appearance: the exterior appearance must blend in with the existing house and the neighbourhood
Length: the max length of rear extensions is 3m for terraced or semi-detached houses, up to 4m for detached houses
Width: the width must be less than 50% of the width of the existing house
Keep in mind that the rules for permitted development are stricter in designated areas.
CERTIFICATE OF LAWFUL DEVELOPMENT