(a) Walls and ceilings shall be maintained free from cracks and openings which would permit flame or excessive heat to enter the concealed space.
(b) In buildings of mixed occupancy, nonresidential space shall be separated from residential space by approved fire separations which will retard the spread of fire.
(c) Garages in or attached to a residential building shall be separated from other spaces in the building by approved fire separations which will retard the spread of fire and prevent flammable or toxic vapors originating within the garage from being transported to other parts of the building.