Fire divisions shall be constructed of noncombustible materials or assembly of noncombustible materials to provide the fire-resistance ratings required by table 5-2. Vertical fire divisions shall be continuous between foundation, roof, or horizontal fire divisions, and through any concealed space in floor or roof construction. Horizontal fire divisions shall be continuous between exterior walls and/or vertical fire divisions.
(a) When roof construction is combustible on both sides of a vertical fire division, the vertical fire division shall extend through the roof construction to a height of at least four inches above the high point at the roof framing. Decking shall tightly butt the fire division. Above the decking of roofs that are flatter than twenty degrees to the horizontal, blocking shall be constructed to form cants on both sides of the fire division with slopes not steeper than 1:4. Combustible decking shall not extend over the top of the fire division.
(b) Except as required in subdivision (c) of this section, when roof construction is noncombustible on one or both sides of a vertical fire division, the vertical fire division may terminate at the underside of the noncombustible roof construction provided the junction of the wall and roof construction is made smoke tight.
(c) When a vertical fire division is required by table 5-2 to have a fire-resistance rating of three or four hours, and the roof construction has a fire-resistance rating of less than two hours, the fire division shall extend above the roof construction to form a parapet at least three feet high.
(d) Fire divisions shall be so constructed that the removal or collapse of construction on one side will not endanger the support of construction on the other side.
(e) Fire divisions shall be made smoketight at their junction with exterior walls. In buildings of construction class II-D and II-E, exterior walls shall be constructed of noncombustible materials for a distance of at least eighteen inches on each side of the fire division, or the fire division shall project at least twelve inches through the exterior wall.
(f) Fire divisions may be offset if the construction between the offset divisions, including their supports, has at the same fire-resistance rating as the fire division, with all hollow spaces within the construction firestopped with noncombustible material.
(g) Where combustible members such as joists, beams, or girders bear on, or frame into, vertical fire divisions, such members shall not extend through the wall and shall have at least four inches of solid noncombustible material below, at the sides, and at the ends of each such member.
(h) Chases or recesses shall not be cut into fire divisions so as to reduce their thickness below that required for the fire-resistance rating.
(i) Vertical fire divisions that are hollow shall be firestopped with at least four inches of noncombustible material so as to prevent passage of flame, smoke, or hot gases through the hollow spaces to the story above or below, or to hollow spaces within connecting floor or roof construction.