From: John Rose <jrose36(--nospam--at)earthlink.net>
Date: Tue, 06 Apr 1999 23:11:24 -0700
No problem in using 23/32" wood structural panels (plywood or OSB) for diaphragms
with roof framing spaced 48" oc; check vertical load capacity (LL and DL) to make
sure that it meets requirements. Diaphragm tables in UBC apply to this
construction, blocked or unblocked as required. If blocked construction is
necessary, it's often done with T&G panels (APA Rated Sheathing 48/24 - special
order; or APA Rated Sturd-I-Floor 24oc) with sheet metal strip stapled to
sheathing over T&G edges. Also can be done with square edge panels (two panel
edge clips between each support) with sheet metal strip for blocked diaphragms,
or with blocking. For unblocked diaphragms, use T&G panels or square edge panels
with blocking. Highest diaphragm shear values are obtained with 10d common
nails, but 8d common nails (min.) could be used with tabulated shear values for
that fastener size. Note if framing is spaced 48" o.c., nailing on intermediate
supports must be 6" oc (for wind uplift), not 12" oc as typically used.
John Rose/APA, Tacoma, WA
> David -
> I've never seen horizontal values for a 48" span of unblocked 3/4" plywood,
> which doesn't mean they don't exist. You may try calling APA. As a side
> note, I think that 3/4" plywood is only rated to span 48" maximum for roof
> vertical loads when the edges are blocked, unless you use T&G plywood or
> panel clips. See Table 23-I-S-1 in the 1994 UBC. This may force the
> blocking issue anyway.
> Bruce Resnick, SE
> Parker Resnick Str. Eng.
> In a message dated 4/2/99 10:42:04 AM Pacific Daylight Time, DHLAssoc(--nospam--at)aol.com
> << I have a commercial project where the architect wants to use exposed 3/4"
> plywood over exposed 4x rafters at 48" o.c. He does not want to see any
> blockings between the rafters. Prelim calcs show maximum diaphragm shear to
> be around 150 plf. Does anyone know--- for plywood horizontal diaphragm
> values; if there is any place in the UBC where one can find diaphragm shear
> values for framing member spacing more than 16" o.c.?