Most efficient use of 3/4″ polyiso on exterior (polyiso is foil faced on both sides)
My home is standard built- 2×3’s 16″ oc w/craft faced fiberglass ins not very well installed( gaps,etc.). I have enough 3/4″ f f polyiso to cover it. FH’s recent articles indicate Roxul batts would be best way to insulate, but I already have the foam.
I’m trying to build the most efficient way. Question is, what’s the best way to utilize existing materials 1) 2 3/4″ sheets together 2) one 3/4″ dead air space between the two sheets 3) two 3/4″ dead air spaces, one at the sheathing & other between the sheets? I’ll be taping sheets w/ foil tape to create air tight integrity and having a 3/4″ space behind the siding with air gaps at top & bottom. The dead air space(s) would be sandwiched w/foam at top & bottom.
OR , is there another way you might suggest I approach this to maximize my materials to get most efficient results?
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