chris, is this the section you needed. There are exceptions like beams can project 6" below the ceiling and an exception for sloped ceilings.
R305.1 Minimum height.
Habitable rooms, hallways, corridors, bathrooms, toilet rooms, laundry rooms and basements shall have a ceiling height of not less than 7 feet (2134 mm). The required height shall be measured from the finish floor to the lowest projection from the ceiling.
pc1