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Re: Valley Rafters

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Charles,
 
        I suspect that the roof sheathing is acting in diagonal tension providing a very deep V shaped plywood web beam along the valley.  The valley beam cannot deflect unless there is significant in-plane deformation of the sheathing or the nailing securing the sheathing to the valley beam fails.  No deflection means no stress according to Hook's Law.
 
        Now trying to prove that may give you something significant to think about.
 
Regards,
 
H. Daryl Richardson
----- Original Message -----
Sent: Saturday, February 07, 2009 8:23 PM
Subject: Valley Rafters

An architect client asked me to answer a building official's request to verify the strength of a valley rafter (or beam) in a wood roof. The architect specified a valley rafter 2" deeper than the rafters (as usual), but this time he is being challenged to prove it. I analyzed it as a simple beam taking half the tributary load from the jack rafters framing into it and it is in fact way off! The architect maintains that he and everyone he knows have always spec'd 2" deeper for decades with no failures or even challenges. He even showed me text books and other reference books with this recommendation. Am I missing something?
Charles O. Laines, S.E.
LAINES ASSOCIATES, LONG BEACH, CA
 
 


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