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Re: More Plywood Diaphragm's

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We don't specifically address it in the 2005 SDPWS Commentary. However,
it looks like we tried to clarify it in the 2008 SDPWS section which states
that both blocked and unblocked diaphragms shall be constructed as

"The width of the nailed face of framing members and blocking shall be
2" nominal or greater at adjoining panel edges except that a 3" nominal
or greater width at adjoining panel edges and staggered nailing at all
panel edges are required where:
a. Nail spacing of 2-1/2" on center or less at adjoining panel edges is
specified, or
b. 10d common nails having penetration in to framing members and
blocking of more than 1-1/2" are specified at 3" on center or less at
adjoining panel edges."

So, my interpretation is if you have 2" nominal framing or blocking for
intermediate members for field nailing, you would use the lower
tabulated value that corresponds to the Minimum Nominal Framing Width of
2". I'd be interested to know if you all have seen or specify 2x
blocking or intermediate framing with 3x framing at adjoining panel
edges? Seems like that could be potentially confusing for the

Not sure of the background on that, but Tom Skaggs at APA could probably
shed some light or weigh-in if I'm wrong.



John "Buddy" Showalter, P.E. 
Director, Technical Media 
AF&PA/American Wood Council 
1111 19th Street, NW, Suite 800 
Washington, DC 20036 
P: 202-463-2769 
F: 202-463-2791 

The American Wood Council (AWC) is the wood products division of the
American Forest & Paper Association (AF&PA). AWC develops
internationally recognized standards for wood design and construction.
Its efforts with building codes and standards, engineering and research,
and technology transfer ensure proper application for engineered and
traditional wood products.

The guidance provided herein is not a formal interpretation of any AF&PA
standard.  Interpretations of AF&PA standards are only available through
a formal process outlined in AF&PA's standards development procedures.


From: "David Topete" <d.topete73(--nospam--at)>
To: seaint(--nospam--at)
Subject: Re: More Plywood Diaphragm's

Note "d" is in the nail size column for 10d nailing... note "c" takes
precedence at the tighter nail spacing. And, i agree that note "g"
allows 2x intermediate members for field nailing. It leads me to believe
that the you can use either value listed. Obviously the lower value
would be more conservative for your design... I'll be curious to check
the NDS Commentar= y for an explanation on the two values being
listed... Good question, Doug.

On Wed, Nov 5, 2008 at 2:33 PM, Doug Mayer
> In Table 2306.3.1 of the 2007 CBC (I would assume this also appears 
> in the 2006 IBC), plywood diaphragms with nail spacing at less the 3" 
> o.c. require 3x framing at all panel edges per note "c" and "d". In 
> light of this, why are there shear values for both 2x and 3x framing 
> members at pa=
> edges and boundaries for nail spacings of 2.5" o.c. and 2" o.c.? Is 
> it because you could still have 2x framing at field nailing? I'm 
> thinking n=
> because note "g" states that "The minimum nominal width of framing 
> member=
> not located at boundaries or adjoining panel edges shall be 2 inches."

> T=
> leads me to believe that the intermediate framing member, as long as 
> it i=
s a
> 2x, does not play a role in the capacities of the diaphragm.
> By the way, where is note "d" in the table? I can't seem to find it. 
> Anyway, what am I missing here? I'm surprised I haven't noticed this 
> apparent contradiction until now. Thanks for any help=85.
> Doug Mayer, SE

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