I’m trying to work out which building serves as the reference point for the Permitted Development rule regarding Section E buildings (garden sheds etc) which requires all development more than 20m from the house to be limited to 10m2. Hopefully you can see a drawing below (not to scale). All existing buildings are 100+ years old. The first drawing shows the site in 1948, with the red line showing the curtilage of the property in question. At some point in the 1980’s, the single outbuilding and land to the rear was subdivided into three parts, expanding the curtilage of the property in question as shown. There is only one deed for this curtilage, and it is considered to be the buildings and land associated with a single dwelling house. At various times during the 1990’s, individual home owners converted their sections of the former outbuilding to living accommodation with planning permission. Since then, the front and rear sections of the house in question have been actively used jointly as living accommodation, with neither part functioning individually as self-contained accommodation. So, the question is: which elevation serves as the reference point for the 20m rule when considering placing an outbuilding in the main rear garden? Is it (A) the rear elevation of the rear part of the house, or (B) the rear elevation of the front part of the house? If you have a clear opinion, please explain your reasoning, and your level of confidence. Thanks!