Page 4 goes into little detail. In the areas I've worked in that's the norm, not saying it's correct but warranty on a metal roof involve proper screw placement. We use to use lead capped nails and then the industry went to rubber washer nails and now these screws. I've not seen a problem with rotting rubber washers. If that's the case there would be huge problems with rubber membrane roofs, which I haven't seen. Can't ay that the rubber formulation hasn't changed.
http://files.buildsite.com/dbderived...rived44736.pdf
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