Is it wise to create an airspace between the roof and closed-cell spray foam to allow for venting?
My new home addition has both ridge and eave vents. We were thinking of putting 1- to 2-inch blocking/cleats and a 2" rigid foamboard, then applying 5 or 6 inches of closed-cell spray foam onto that so that there is breathability. The exterior roofing is metal. We were also going to spray-foam the walls built of 2 x 6s. The contractor recommends 3" in the walls. This would create an airspace between the faom and the plasterboard. What do you think?
Although this sounds good, and housewrap companies sell systems to allow this, most foam producers do not recommend this type of installation.
I would contact the producer of the foam (not your contractor) -- tell them exactly your situation and follow their recommendations.
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