The buildings shall be of sound construction and kept in good repair, and shall be of such construction as to prevent the entrance or harboring of vermin.

(a) Outside openings.

(1) The doors, windows, skylights, and other outside openings of the plant, except receiving rooms and live rabbit holding rooms, shall be protected by properly fitted screens or other suitable devices against the entrance of flies and other insects.

(2) Outside doors, except in receiving rooms and live rabbit holding rooms, shall be self-closing and so hung that not over 1⁄4 -inch clearance remains when closed. Screen doors shall open toward the outside of the building.