On a corner lot which abuts a key lot no accessory building shall be nearer the street side lot line than a distance equal to the depth of front yard required on the key lot; provided, however, that this restriction shall not be so applied as to reduce the permitted depth of the accessory building to less than twenty (20) feet. Where the rear lot line of a corner lot in an R district abuts the rear lot line of another lot, no accessory building shall be nearer the street side lot line than the main building or in any case be located less than ten feet from the side lot line. (Prior gen. code § 8-60.28)