Is it worth the cost to add polyiso on top of my EPS roof insulation stack?
My plan is to use 2 staggered 4″ layers of EPS. Note that these are from ICF forms and are only 12″x 48″ boards – They do have interlocking tabs, but there will be a LOT of seams. As I already have my screws to connect my OSB to the bottom layer, I only have an additional 1/2″ of space to add polyiso. Is it worth the cost/effort to add a 1/2″ layer of polyiso on top of the EPS? Foil faced? Foil up or down? Thanks for any advice
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