Hi - any input would be appreciated: Permitted development only applies to houses, not flats or apartments. We own an entire physical building, three stories high. The INSIDE of the top two floors are subject to a 1000 year lease, owned by another family. It has it's own access. There are no shared spaces. The lease stipulates that we own the roof, exterior walls etc. ie. it is physically our entire building - we are the ones legally obliged to insure the whole thing. We then live in the ground floor. My question is, as far as permitted development is concerned - do we own a house or a flat? Any thoughts?