metal roof over foam
hello, I am installing a metal roof over foam sheets, its the box store type panel with exposed screws. the roof is as follows… 7/16 zip taped and sealed to rafters, 2 layers of 2 inch polyiso taped, staggered and sealed and here is where my issue lies, I was going to put down a layer of 5/8 zip, taped and sealed, with long screws going into rafters but all the screws seem to stand a little proud of the zip. I was told this would rub on the roof panels causing wear and/or rust issues. I have used strapping in the past and countersunk the screws, what do you do with sheet goods? I tried lining up the ribs in the panel with the screwa but the rafters are 16″ oc and the ribs are 6″ oc. thanks for any help.
Darren Williams
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Replies
If you are using roofing deck screws, you can get plastic washers for them. This would keep the screw head away from the roof.
If you are not in a windy area, you can also go with flush mount (bugle head) screws instead of the truss headed ones.
I think a synthetic underlayment may be in order. It would act as a "slip sheet" for the whole roof and a barrier at the screws and the tape. It would also cover any overdriven fasteners.