No building hereafter erected or enlarged, or altered so as to change its classification as to occupancy shall be used in whole or in part until a certificate of occupancy shall have been issued therefor, except that if the building shall be used or occupied during any alteration work, such use or occupation shall not continue for more than thirty (30) days after completion of the alteration work, unless a certificate of occupancy shall have been issued. (1965 Code §67.10)