Upon application by the owner of such a building or open lot in existence prior to January 1, 1938, the commissioner shall issue a certificate of occupancy for such building, provided that at the time of issuing such certificate, such existing building is in compliance with all retroactive requirements of the 1968 building code applicable to such building and no notices of violation or other notices or orders affecting the building as they relate to the provisions of this code or the 1968 building code are pending before the department, and provided further that it is established to the satisfaction of the commissioner, after inspection and investigation, that the alleged use of the building has heretofore legally existed.