Fire Spread in Concealed Building Spaces
Flames, smoke and gases from a fire will spread through a building taking the path of least resistance, through concealed spaces and voids in the building construction. Fire stopping (or fire blocking) in combustible construction, such as at the floor/ceiling level in a concealed wall space with parallel rows of wood studs, is intended to reduce the spread of fire, smoke and gases through concealed spaces and voids. Fire stopping is commonly achieved using 2" nominal lumber. Draft stopping in combustible construction, such as in an attic area, is intended to act as a barrier to smoke and gases. Draft stopping is commonly achieved by sheathing material such as ½" gypsum board or 3/8" plywood. Details on the requirements for the location of fire stopping and draft stopping, and the materials approved for use as fire stopping and draft stopping, are found in the Life Safety Code (NFPA 101) section 8.6.10 and the International Building Code, section 717.