The International Building Code, or IBC, is a set of standards compiled by the International Code Council, or ICC. Adoption of these building standards is optional, but most U.S. municipal, county and state jurisdictions base their local code requirements on the IBC or the International Residential Code (IRC), the standard code reference for one- and two-family houses and townhouses. It's important to note that local building code supersedes IBC and IRC requirements, so always follow local code for your own building projects.
International Building Code
The International Building Code is used for commercial buildings and any building that contains more than two dwelling units, such as apartment buildings. Minimum ceiling height in these buildings must be 7 feet 6 inches in hallways, common areas and habitable rooms.
International Residential Code
According the the IRC, all habitable rooms must have a minimum ceiling height of 7 feet. Habitable rooms include bedrooms, living spaces and kitchens but exclude bathrooms, hallways, utility spaces and closets. A ceiling with exposed beams spaced at least 4 feet apart can measure 6 feet 6 inches from the floor to the underside of the beams. Minimum ceiling height in bathrooms is 6 feet 8 inches.
The minimum ceiling height in rooms with sloped ceilings (such as a finished attic space) is 7 feet over at least 50 percent of the room area. Room area is this case is calculated as the total floor space with walls at least 5 feet tall. Areas with ceilings lower than 5 feet are allowed but do not count toward the official room area total (IRC rules also include minimum floor space for most habitable rooms).
Under the IRC, basements with no bedrooms or living areas may have ceilings 6 feet 8 inches high with beams and ductwork at a minimum height of 6 feet 4 inches.