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FIRE AND SMOKE PROTECTION FEATURES bly is equal to the sum of the time assigned to the mem- o = G brane on the fire-exposed side,the time assigned to the framing members and the time assigned for additional rill: contribution by other protective measures such as insula- tion.e - The membrane on the unexposed side shall not be included in determining the fire resistance of the assem- bly. 721.6.2.2 Time assigned to membranes. Table er et 721.6.2(1)indicates the time assigned to membranes on 0=920-2d-2w 0=2dmr the fire-exposed side. 721.6.2.3 Exterior walls.For an exterior wall with afire FIGURE 721.5.2 separation distance greater than 5 feet(1524 mm),the DETERMINATION OF THE HEATED PERIMETER wall is assigned a ratingdependent on the interior OF STRUCTURAL STEEL BEAMS AND GIRDERS g P mem- brane and the framing as described in Tables 721.6.2(1) 721.5.2.3 Structural steel trusses.The fire resistance of and 721.6.2(2). The membrane on the outside of the structural steel trusses protected with fire-resistant mate- nonfue-exposed side of exterior walls with afire separa- 524 rials sprayed to each of the individual truss elements tion distance greater than 5 feet d sidi mm)may consist shall be permitted to be determined in accordance with of sheathing,sheathing paper and siding as described in this section. The thickness of the fire-resistant material Table 721.6.2(3). shall be determined in accordance with Section TABLE 721.6.2(1) 721.5.1.3. The weight-to-heated-perimeter ratio (W/D) TIME ASSIGNED TO WALLBOARD MEMBRANES•a.,s of truss elements that can be simultaneously exposed to DESCRIPTION OF FINISH TIME*(minutes) fire on all sides shall be determined on the same basis as 3/8-inch wood structural panel bonded with columns,as specified in Section 721.5.1.1.The weight- exterior glue 5 to-heated-perimeter ratio (W/O) of truss elements that directly support floor or roof assembly shall be deter- 15/32 inch wood structural panel bonded with 10 reined on the same basis as beams and girders,as speci- exterior glue t‘ saw fled in Section 721.5.2.1' i9/13 inch wood structural panel bonded with exterior glue 15 The fire resistance of structural steel trusses protected with intumescent or mastic fire-resistant coatings shall 3/8-inch gypsum wallboard 10 be determined on the basis of fire-resistance tests in accordance with Section 703.2. 48-inch gypsum wallboard 15 721.6 Wood assemblies.The provisions of this section contain 5/8-inch gypsum wallboard / Z _ I110 ,.— 30 procedures by which the fire-resistance ratings of wood 1/,-inch Type X gypsum wallboard 25 assemblies are established by calculations. 721.6.1 General.This section contains procedures for cal- s/a inch Type X gypsum wallboard 40 culating the fire-resistance ratings of walls, floor/ceiling Double s/a inch gypsum wallboard 25 and roof/ceiling assemblies based in part on the standard I/Z inch+t/8-inch gypsum wallboard 35 method of testing referenced in Section 703.2. Double I/2 inch gypsum wallboard 40 721.6.1.1 Maximum fire-resistance rating.Fire resis- tance ratings calculated for assemblies using the meth- For SI: 1 inch=25.4 mm. ods in Section 721.E shall be limited to a maximum of 1 a. These values apply only when membranes are installed on framingmembe which are spaced 16 inches on. hour. - b. Gypsum wallboard installed over framing or firing shall be installed so that 721.6.1.2 Dissimilar membranes. Where dissimilar all edges are supported,except inch type X gypsum wallboard shall be membranes are used on a wall assembly,the calculation ertained to be installed horizontally with the horizontal joints staggered 24 Yinches each side and unsupported but finished. shallbe made from the leastfire-resistant(weaker)side. c. On wood frame Floor/ceiling orroof/ceiling assemblies,gypsum board shall 721.6.2 Walls,floors and roofs.Thesea 1 to be installed with the long dimension perpendicular to framing members and proceduresapply shall have all joints finished. both load-bearing and nonload-bearing assemblies. d. The membrane on the unexposed side shall notbeincludedindemmining the fire resistance of the assembly When dissimilar membranes are usedona wall astem- 721.6.2.1 Fire-resistance rating of wood frame assem- bly,the calculation shall be made from the least fire-resistant(weaker)side. blies.The fire-resistance rating of a wood frame assem- e. The time assigned is not a finished rating. 2010 OREGON STRUCTURAL SPECIALTY CODE 177