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RE: CMU Wall Supported by Plywood Sheathed Roof Diaphragm and She arwalls

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Section 2315.2 of UBC addresses this issues. However, this is probably one
of the most overlooked sections of the code when it comes to design or plan
check. I can tell you that you may even find many buildings using masonry
area separation walls up to 4 stories relying entirely of wood shear walls
for lateral resistance. So it doesn't surprise me that the contractor is
claiming he has seen it before. But, if you don't meet the criteria in the
code, it is definitely not compliant. However, if you can convince yourself
and the code authority that the deflections are acceptable, you may want to
try applying for alternate method & material application per section

Ben Yousefi, SE
San Jose, CA

	-----Original Message-----
	From:	Monty Hart [SMTP:montyh(--nospam--at)]
	Sent:	Wednesday, February 21, 2001 10:48 PM
	To:	seaint(--nospam--at)
	Subject:	CMU Wall Supported by Plywood Sheathed Roof
Diaphragm and Shearwalls

	I'm working on a proposed one story 50' x 80'  warehouse in seismic
	4.  Exterior walls are 8" metal studs sheathed with plywood and are
	high to the roof deck.  Roof is open web wood joists with a plywood
	diaphragm.  One of the 80' long walls is adjacent to (with a 4" gap)
	CMU wall of an existing building.   The existing building and the
	building are on different lots, so the buildings can not be
	The new wall needs to be a firewall, and must be finished on the
	interior and exterior sides, with only a 4" clearance for installing
	exterior sheathing.  I would prefer to try sheathing a stud wall
flat on
	the slab and then tilting it up, or installing temporary bracing,
	the studs in a vertical position about 4 ft from the existing wall
	then slide the new wall into place.   Neither I nor the contractor
	seen a metal stud wall erected in this way, so the contractor is
	insisting on a single 80' long, 23' high CMU wall.  I am extremely
	reluctant to support such a wall with a plywood sheathed roof
	supported by plywood sheathed shear walls because of the potential
	excessive deflection at the top of the CMU wall, which may result in
	cracking of the concrete block.    I have not yet calced the
	but I assume it would be in the 1" to 2" range at the top of the CMU

	The contractor says he has seen other buildings constructed with a
	single CMU fire wall.  Unfortunately, I can not find any section of
	'97 ICBO Code that would prevent it or even address the allowable
	out-of-plane deflection for a CMU wall.   I would appreciate any
	comments regarding applicable code requirements or experience with
	failures of similarly constructed buildings.  I would also like any
	recommendations about installing plywood sheathing on a metal stud
	with only 4" of clearance.

	Thanks in advance for any comments,

	Monty Hart
	Associated Design Consultants, Inc.
	Anchorage, Alaska