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RE: Plywood sheathing on wood trusses

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Are these pre-manufactured plated trusses or field stick framed?  If
trusses, specify a beveled top chord.  Most manufacturers can easily do

If stick frame, and if the forces require it, specify beveled joists.  A
skilled carpenter with a table saw could put a beveled surface on all the
joists for a decent sized house in a matter of hours, but you probably only
have a small number that require it.  If the contractor doesn?t have a table
saw on site you probably need a better contractor.

Jason Kilgore
Leigh & O'Kane, LLC
Kansas City, Missouri
From: Jim Wilson [mailto:wilsonengineers(--nospam--at)] 
Sent: Wednesday, October 13, 2004 8:55 AM
To: seaint(--nospam--at)
Subject: RE: Plywood sheathing on wood trusses

Thanks for the advice!  I haven't designed a plywood diaphgram before and
wanted to make sure there weren't any particular no-no's to look out for. 
I'll keep your thoughts in mind and if the design loading doesn't end up too
high, I won't worry about it.

If it does get too high, I'll add in the molasses!
Jim Wilson, PE
Stroudsburg, PA

Keith De Lapp <keith(--nospam--at)> wrote:
Shimming a 3/16" thickness doesn't seem practical.  Splitting would be my
big concern.  I would take a look at the demand/capacity ratio.  If it's
high I would require a shaped nailer along side the top chord.  If it's not
high I would inspect for shiners and let it go.  The situation you describe
is common on hip roofs.
Keith De Lapp, P.E.
-----Original Message-----
From: Dennis Wish [mailto:dennis.wish(--nospam--at)]
Sent: Tuesday, October 12, 2004 12:58 PM
To: seaint(--nospam--at)
Subject: RE: Plywood sheathing on wood trusses
This is a tough call. I think the issue here is that the shear transfer
through the diaphragm creates an opportunity for bending in the exposed nail
shaft and/or greater chance of pull-out through bending of the nails. In a
tight connection, the bending issue is almost non-existent as the shear is
tightly transferred from wood to wood. 
So the question then comes it shimming the wood would provide adequate shear
transfer. I would prefer to use a nailer to the side of the truss ripped at
the angle causing the 3/16 gap and then boundary nail the sheathing to the
nailer  like molasses flowing through the load path from wood to nail to
wood to nail. This might confuse some, but Ive always considered the
Molasses metaphor as ideal in understanding load path transfer from roof to
Sorry about the simplicity of this  but I try to understand how the
materials will work together in light-framing rather than to try and analyze
any one component.
Dennis S. Wish, PE
California Professional Engineer
Structural Engineering Consultant
"Apathy is Lethal!" Speak out and Vote - but make sure you getthe facts
right without the spin from either side; Verify their claims at
-----Original Message-----
From: Jim Wilson [mailto:wilsonengineers(--nospam--at)] 
Sent: Tuesday, October 12, 2004 12:16 PM
To: seaint(--nospam--at)
Subject: Plywood sheathing on wood trusses
Does plywood sheathing need to be flat against the top chord of supporting
wood framing to be acceptable/effective?  I have a case where wood trusses
are not parallel to the pitch of a roof, and therefore, the plywood will
rest on one edge of the top chord, but be approximately 3/16" off of the
other edge.  
Jim Wilson
Stroudsburg, PA
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