What is the minimum basement ceiling height, and can beams or ducts hang lower?
Non-habitable basement areas need 6 ft 8 in, and beams, girders, or ducts may project down to 6 ft 4 in above the floor (IRC R305.1.1).
Under the 2015 IRC, basement portions that do not contain habitable space, hallways, bathrooms, toilet rooms, or laundry rooms must have a ceiling height of at least 6 feet 8 inches (2032 mm).
Beams, girders, ducts, and other obstructions are allowed to project down to within 6 feet 4 inches (1931 mm) of the finished floor. Basement areas that do contain habitable space still meet the 7-foot rule of R305.1.
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