huangyhg

design-of-firewall
a plan for a 15,000 square foot 1 storey church with
stud wall construction and timber wood trusses calls for
a firewall. i proposed to the architect to use 2- 6" block walls reinforced and laterally supported at the
ceiling and at the top of the truss (truss top chord).
the architect suggested to use only 1 - 8" reinforced wall, because another engineer had used the same detail on a another project but it was steel construction. the
code requires that the wall must be designed so that
it does not collapse during the event of a fire on 1 side of the wall. there are no references on how to design a firewall to support the collapse of the adjacent supported trusses, etc. i disagree with the architect, and still using the 2 - 6" walls. anyone with suggestions on designing a single firewall? much appreciated.
the references that i have found useful are:
nfpa
ncma
factory mutual
the canadian code
for a one story structure, it is common to use a reinforced masonry firewall cantilevered from the foundation (depending upon height and seismic zone) and independent from the structure on each side. normally, i use 12" reinforced cmu for cantilevered firewalls, not 8".
another option (more expensive) is to use two firewalls, one tied to each structure. one wall will be left standing if one structure collapses under fire conditions. doors and openings complicate the detailing but it certainly can be done.
i hope this helps!
i have done the one firewall with independent structure but i have not done the double wall before, but have heard of it being done. for the 2 wall case, i suppose if one side collapses due to fire then that side would pull its tied wall away from the adjacent firewall and not push into it, possibly causing another collapse.

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