It is the duty of the chief of the fire department to inspect or cause to be inspected by fire department officers or members, as often as may be necessary, but not less than twice a year in outlying districts and four times a year in the closely built portions of the city, all buildings, premises, and public thoroughfares, for the purpose of ascertaining and causing to be corrected any conditions liable to cause fire, or any violations of the provisions or intent of any ordinance of the city affecting the fire hazard. In private dwellings such inspections shall be restricted to basements and cellars.