For yards in the A-P zone, the provisions of the R-3 district shall apply, except, when an entirely new building is constructed for administrative professional office uses only, the rear yard may be reduced to not less than five feet (5'). The rear yard shall be increased two and one-half feet (21/2') in depth for every story above the second story. (Ord. 1000 § 21.40(D), 1955)