A. Where the lot abuts an alley, no rear yard shall be required for one story buildings.
B. Where the lot abuts an alley, a rear yard of ten feet shall be provided for the two story parts of buildings.
C. Where the lot does not abut an alley, there shall be a rear yard having a depth of not less than twenty feet, unless the lot is a lot of record on or before February 12, 1971 and is less than one hundred feet in depth, in which case, the rear yard need not exceed twenty per cent of the depth of the lot. (Prior code § 11-3-3 (e) (3))