DESIGN ALERT ON SHAFT WALLS
ISSUE:
Construction of 2-hour rated shaft walls.
BACKGROUND:
On a recent project, an A/E incorrectly showed construction of 2-hour rated shaft wall.
DISCUSSION:
To illustrate this problem, the A/E showed 3-1/2" studs and concrete backer board for
shaft walls. The contractor pointed out that this would not provide a 2-hour rated wall
construction and requested a change. The contractor was correct. To ensure wall
ratings, UL and other testing organizations test wall assemblies of manufacturers, and
list their assemblies. Any substitute or anything untested and unlisted would not be
acceptable.
RECOMMENDATIONS/CONCLUSION:
1. Only tested assemblies of manufacturers should be specified. For instance, UL
Design U411 or U412 listed in UL Fire Resistance Directory, 1995, Volume 1, are 2-
hour tested assemblies for non-bearing walls. Basically, they include two layers of 5/8"
or 1/2" gypsum wall boards on each side and 25 gauge 2-1/2" or 1-5/8" metal studs 24"
o.c.
2. Review tested assemblies of walls etc., before specifying. Contact Satish Sehgal at
202-565-5032 in Standards Service (187C) if you need any additional information, or
the Regional Safety and Fire Protection Engineer for station level projects.
.
31 August 1995
FM-187C-DA40
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