Class A underlayment assembly order for a ZIP deck & metal roof
Looking for a straightforward way to do a ZIP roof deck and metal roof to meet Class A in wildfire country, when I’m guessing I’m going to want underlayment better than the bare minimum between the two.
1. Does putting gypsum on *top* of a 5/8″ ZIP roof deck make sense for this case (or any case)?
2. Since it’s pulling teeth to get 5/8″ ZIP where I am, can gypsum instead directly below a 7/16″ ZIP deck both meet minimum deck thickness, and, work equally well as underlayment in that order, leaving the top of the ZIP unmolested to be air and bulk water barrier?
3. What’s a better way? Cost, efficacy, buildability.
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