What duct needs to be restrained?
All ductwork that is 6 square feet and over in cross-sectional area or over 17 lb./ft. and does not fall into another exemption category shall be restrained to meet the applicable building code. Other exemptions that may apply include ductwork that has not been assigned an importance factor of 1.5 and is part of a building with a Seismic Design Category (SDC) of C, C, E or F; and all ductwork in a SDC A or B building. (This is based on IBC 2012 and ASEC 7-10 requirements.)