Reply to "Fire Resistance Rating of a proposed design"

Fire resistance in a wall assembly is a two-way system. Only the membrane facing the fire exposure and its supporting structure are effective in providing fire resistance--the membrane on the opposite side has very little to no affect on the overall fire resistance of an assembly. Therefore, you only have 2 layers of gypsum board, plus the framing, providing fire resistance. With a double framed wall, the insulation only helps the side in which it is installed; thus, you have a nonsymmetrical wall assembly and the overall wall fire-resistance rating is based on the weaker (i.e., noninsulated) side per IBC Section 703.2.1.

However, I think a similar assembly will work based on GA-600 Assembly File No. WP 3820, which is a generic system (thus allowed by the IBC). It will be about an inch wider, though, and the studs will need to be at 16 inches o.c. There is no need for insulation, but it can be added for sound transmission quality purposes as indicated by the assembly.

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