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Double fire wall horizontal continuity

Question asked by on Sep 14, 2017

When using NFPA 221 provisions for the use of a double fire wall, how is horizontal continuity to be addressed when each wall terminates differently, and at 90 degrees to each other?  Are the two walls able to terminate differently, or must they be looked at as the two combined make "one" wall and must terminate the same?  At an exterior wall intersection that is less than 180 degrees, does the wall that continues in plane have to only extend the 18" whereas the other wall would be able to stop at the exterior non-combustible sheathing of the perpendicular wall at the intersection?  Please see attached.  The IBC expressly addresses these less than 180 degree conditions, but NFPA does not appear to. Nor does NFPA 221 clarify if each wall of the double wall condition can be independently looked at for continuity requirements.  Thank you in advance for your input.