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Reattaching a subpurlin to a diaphragm

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I am looking at some roof repairs (yeah, I've finally made the "Big Time") at a commercial structure. It is a typical panelized roof with 2X4 sub purlins spaced at 24" spanning 8'-0". These sub purlins are attached to the purlins with FN hangers. Somewhere along the line, moisture got between the roofing membrane and the insulation foil which allowed corrosion to attack the FN hangers. Recently, one sub-purlin failed. Fortunately, no one was in the space at the time.

 

The question I have is regarding the attachment of the replacement sub purlin to the existing roof diaphragm. Of course, the owner would rather not remove the existing roofing to re-nail from above. However, considering that the diaphragm is probably only 1/2" thick, I really don't see any other way. Some of the sub purlins are attached at the panel edge some are not but the only way to know that is to remove the roofing.

 

Does anyone have any ideas?

 

TIA,

 

 

T. William (Bill) Allen, S.E.

ALLEN DESIGNS

Consulting Structural Engineers
 
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