Class II (Buildings not frequented by people)

A detached building—

     (a) into which people do not normally go; or

     (b) into which people go only intermittently and then only for the purpose of inspecting or maintaining fixed plant or machinery,

unless any point of such a building is less than one and a half times its height from

          (i) any point of a building into which people can or do normally go; or

          (ii) the nearest point of the boundary of the curtilage of that building,

whichever is the nearer.