2000 IBC, Section 1003.2.5.1 Protruding objects are permitted to extend below the minimum ceiling height required by section 1003.2.4 provided a minimum headroom of 80 inches (6'8") shall be provided for any walking surface, including walks, corridors, aisles and passageways. Not more than 50% of the cieling area of a means of egress shall be reduced in height by protruding objects.