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Re: [SEAOC] Re: Substitution of OSB for plywood sheathing

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I have heard of several problems with OSB sheathing which are as follows:
     1.   It is very hard to visually verify nail spacing since the nail
heads blend in with 
           the surface of the OSB sheathing as opposed to traditional plywood
which is 
           lighter and uniform in color and the nails stand out .

      2.  When OSB gets wet, the sheathing expands, pulling the nail heads
through the  
           sheathing, thereby reducing the effective sheathing thickness for
shear                         resistance.  Once OSB gets wet and expands, it
typically does not shrink back.

      3.  When sawing the OSB sheathing you do not get the same straight
smooth edge            as compared to plywood.  The concern is the reduced
sheathing edge integrity            related to edge nailing.  Are the nails
more likely to pull through sooner            when the sheathing is laterally
loaded because of the potential damaged edge            condition. 
       4.  I have also heard that the shear values for OSB are actually less
than for             plywood so direct subsitution may not be permissable.

The best source would be to contact APA  directly which may agree or disagree
with what I have said above. The aboved mentioned items are things I have
heard from various members of SEAOSC.

Michael Cochran
Brian L. Cochran Associates
Los Angeles, CA
BCASE 1356(--nospam--at)