Sheathing between foil-faced polyiso and closed-cell spray polyurethane foam
I’m working on the details of an R-40 Wall in Southern Indiana, Northern Climate Zone 4. Please see the attached file.
Among many options is to use 2″ of properly layered, sealed and taped FFPIC [foil-faced polyisocyanurate] exterior to the sheathing and an Advanced Framed stud cavity filled with CCSPF [closed-cell spray polyurethane foam] on the interior. The house will have 3′ Overhangs, Brick Cladding, and a 1″ Rain Screen.
Will sandwiching sheathing (weather Plywood or OSB) between FFPIC & the CCSPF create a condition which traps moisture and causes damage to the sheathing ? It would seem that construction and materials would keep moisture out, but I’m concerned that any moisture that did enter the sheathing would have a difficult time drying.
Is there any advantage to the Impermeable Liquid Applied Air/Water Barrier in this installation, or is it just superfluous ?
Would that assessment change if the LAA/WB was permeable vs. impermeable?
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