Paul Webb
9/18/2009
The plan is to remove the existing roof. Install common trusses with a 4/12 pitch then attach 2x4 purlins on the trusses to attach the metal roofing. Do I need plywood decking with an underlayment on the trusses? Can the underside of the metal be exposed to the attic? Would reinforced plastic placed over the trusses work? I plan on adding blown in insulation and having a ridge vent.
Ken Buchinger
NCI Building Systems, Inc.
9/18/2009
This will work if: (1) you use a strucutral panel that is capable of handling the purlin span. I would suggest an engineer provide this info based on span tables from the manufacturer whose product you intend to use. You will have to design for snow loads. (2) if you are going leave the underside of the metal exposed, make sure the attic space is well ventilated to help prevent condensation.
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