Openings to the outside shall be effectively protected against the entry of rodents. Outside openings shall be protected against the entry of insects by tight-fitting, self-closing doors, closed windows, screening, controlled air currents, or other means. Screen doors shall be self-closing and screens for windows, skylights, transoms, intake and exhaust air ducts and other openings to the outside shall be tight-fitting and free of breaks. Screening material shall be not less than 16 mesh to the inch.