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RE: Plywood over 2x Decking for Diaphragm

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Sounds good to me as long as you get the right nail penetration listed in the design tables.  I would be concerned with the boundary nailing though.  At the diaphragm boundary I think you need the nail to penetrate thru the decking into the wall top plates, or whatever your chord/struts are.  You’re looking at 20d’s probably.


~~ Eli Grassley, PE


-----Original Message-----
From: Joe Grill [mailto:jgrill(--nospam--at)]
Sent: Monday, January 23, 2006 2:17 PM
To: seaint
Subject: Plywood over 2x Decking for Diaphragm


I have a project where the client has (so far) provided a floor system consisting of 3/4" plywood over 2x6 T&G decking.  The decking spans 3 ft to 6x10 purlins.  It seems to me that I can use the plywood diaphragm values for a blocked diaphragm assuming nail size (short enough to not protrude clear through the decking) and penetration is taken into account in the diaphragm values.  I think this is the case as all the panel edges are backed up with the decking so the diaphragm can be considered “blocked” and the 2x6 decking will span the 3 ft.


Any thoughts?



Joe Grill


Joseph R. Grill, P.E. (Structural)

Shephard - Wesnitzer, Inc.

Civil Engineering and Surveying

P.O. Box 3924

Sedona, AZ  86340

PHONE (928) 282-1061

FAX (928) 282-2058