In residential zone districts, any change of residential occupancy in a building or structure consistent with the last issued Certificate of Occupancy shall not require a new Certificate of Occupancy; however, any change in nonresidential occupancy in the zone districts in building or structure shall not be effected unless a new Certificate of Occupancy is secured. In nonresidential zone districts it shall be unlawful to use or occupy, or permit the use or occupancy of any building or structure, in whole or in part, for any purpose whatsoever after the ownership or right of occupancy thereof has changed, without first obtaining a Certificate of Occupancy from the Building Subcode Official, except that changes in occupancy related solely to residential uses consistent with the last issued Certificate of Occupancy shall not require a new Certificate of Occupancy.