The required yards surrounding an existing building shall not be separated in ownership from that portion of the lot upon which the building is located, and no part shall be considered as providing a yard for any other existing building on the same or an adjacent lot. A yard shall not be reduced to less than the required dimensions for that district in which it is located by enlarging an existing building, and a yard of less than the required dimensions shall not be further reduced. Every required yard shall be open and unobstructed from the ground upward, except for accessory buildings as set forth in Section 1145.15, and permitted projections as set forth in Section 1145.16.
(1980 Code 151.28)