All approved drawings, specifications, and other papers filed with the application for permit shall be so stamped or endorsed by the Chief Building Official and one set shall be returned to the applicant for a permit, and the certified copies of the same shall be kept on the building or work until the same has been completed. True copies of all or as many of the said drawings, specifications, and statements as may be required in the opinion of the Chief Building Official to illustrate the features of construction and equipment of the building referred to in this Building Code shall be retained by him and shall become records of his office.
(‘74 Code, § 150.30)