Certificate of occupancy. It shall be unlawful to use or permit the use of any building or premises or part thereof hereafter created, erected, changed, converted, altered or enlarged, wholly or in part, or to use any building or premises existing at the time of enactment of this chapter, for any other than the purpose for which it is then being used, until a certificate of occupancy shall have been applied for and issued by the Inspector, as provided in the Building Code.