No building of a higher grade of occupancy shall be converted to the use of a building of a lower grade of occupancy, except as provided in section six of this act, unless it shall be made to conform in all particulars, as to safety in structure and requirements in sanitation and health, to the class to which the lower grade belongs. No building not now in one of the grades referred to in this act shall be converted into any such grade without conforming to all the requirements of this and other acts, and all the rules and regulations relating to such grades.
53 P.S. § 14933