In the performance of his duties and for the purpose of inspection of work being done under a building permit or without a building permit contrary to the provisions of this Building Code, the Building Inspector has authority to enter into and upon any building or lot. During the progress of work, he shall make at least three inspections, the first at the completion of the footings and foundation, previous to backfilling; the second on completion of framing and outside covering; and the third on completion of the building, together with such other inspections as he believes necessary. The applicant or his agent shall notify the Building Inspector of the completion of stages of construction as hereinabove set forth.
(‘73 Code, § 1305.03)