Penetration Of Fire Walls
Can a roof truss penetrate a one-hr. tenant separation wall without having a one-hr. rated ceiling? The building official insists that the 2x4 chords are combustible and nullify the integrity of the one-hr. rated partition that is constructed in an attic above an 8 in. C.M.U. bearing wall. The partition consists of gypsum board attached to 2 x 4 stud framing. The building official insists that a ledger must be attached through the gypsum board to support the trusses each side of the wall. This is almost saying that any rated assembly must have bearing only on other rated assemblies. Would you want gypsum board between your truss bearing and the double top plate of a wood stud wall?
You pose some very good questions. Structurally, what the building official is suggesting seems inadequate. You cannot have a gypsum board separation between a ledger and the bearing wall to which it is being attached. One solution that comes to mind is UL U338. This is a non-structural separation of 2x4s on flat, covered with 5/8 in. gypsum board on each side. Gable end frames (truss shapes with vertical studs) are often used with this assembly. Since the assembly is only 2.75 in. thick on the center of an 8 in. CMU wall there is 2.625 in. of bearing on either side for the roof trusses and penetration of the vertical fire assembly is not required. Check with the truss manufacturer to see if this is sufficient bearing for the roof trusses. If not, they should be able to provide you with some method to achieve sufficient bearing under this configuration.
You can also consult SBCA’s Metal Plate Connected Wood Truss Handbook for more information on area separation assemblies; this topic is covered specifically in section 17a and section 17b. For additional information on fire-resistance-rated assemblies, including separation walls, see SBCA Research Report 1509-01: Fire Resistance Rated Truss Assemblies.