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Another related roof diaphragm question

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As I was reading the wood frame roof diaphragm Q&A a question came to mind.
When you have a hip roof which is constructed with plated trusses you will
typically have common trusses at the interior of the roof and as you go
through the hip area you have a hip set roof truss up to a point where a hip
set girder truss is placed 4' or 6' in from the end wall of the building.
Monoslope trusses are then used to complete roof framing and are attached to
the hip set girder truss.

The hip set trusses step down toward the girder truss, but the top chords
are not beveled.  I have seen a number of builders install 2x4 flat purlins
(the purlins are probably nailed to the truss top chords with (2) 10d or 12d
gun nails at each truss top chord) perpendicular to hip set trusses to have
a flat surface to attach the roof sheathing to, but I know this isn't always
done.  I realize that I haven't considered this in my designs and you could
have two sheet edges fall over the top corner of the truss top chord
necessitating toenailing both sheet edges to the top chord of the truss if
purlins, sloped blocking between trusses or bevel cut blocking attached to
the top chord of the truss is not used.

Has anyone considered how this affects the diaphragm strength?  Does anyone
have any standard details they use for this condition?  Mr. John Rose, do
you know if any research has been done or standard details have been
developed for this condition?  Thanks in advance for your comments.

Albert J. Meyer, Jr., P.E.
Martin Engineering
238 North 22nd Street
Philadelphia PA 19103-1004
(215) 665-8570
(215) 561-5064 Fax


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