A main building other than a single-family dwelling on an interior lot shall have two side yards, each having a minimum width equal to the greater of 15 feet, or that distance which, when added to the actual abutting residential lot setback, if any, equals 30 feet, provided, that if such building is over 35 feet in height, the width of each side yard shall be not less than the greater of 20 feet, or that distance which, when added to the actual abutting residential lot setback, if any, equals 35 feet.