In all districts where buildings are erected or structurally altered for dwelling purposes shall be a rear yard having a depth of not less than twenty (20) percent of the depth of the lot, provided such rear yard need not exceed twenty-five (25) feet.

In the “D” and “E” districts there shall be a rear yard having a depth of not less than twenty (20) percent of the depth of the lot provided such rear yard need not exceed twenty-five (25) feet.

In the “F,” “G,” “H,” and “I” districts, when property is not used for dwelling purposes, and when not abutting on the rear of a dwelling district, no rear yard is required. If abutting on the rear of a dwelling district, “A,” “B,” “B-1,” “B-2” or other dwelling districts then a rear yard of at least ten (10) feet is required.

In computing the required bit of a rear yard for any building or such yard abutting an alley, the depth of the lot maybe considered to the center of the alley and the required bit of rear yard measures from the center of said alley.

An accessory building not exceeding one story in height may occupy not more than sixty (60) percent of a minimum required rear yard.

An accessory building exceeding one story in height may occupy not more than forty (40) percent of a minimum required rear yard.