Open-cell foam in an unvented cathedral ceiling
I’m getting quotes from contractors right now to insulate a small cottage with an unvented cathedral ceiling using 2x10s. I’m in zone 3C.
One contractor has suggested spraying 5.5″ of open-cell foam between the rafters and calling it a day. I asked if we could just fill the entire 9.5″ cavity and he said, “You achieve maximum efficiency @5.5. Any more is overkill. It will expand a couple more inches as we will not cut it but leave the excess.”
Code requires R-30 for ceilings around here.
I may be wrong but doesn’t more insulation mean higher R-value?
Is there a maximum efficiency for certain insulation materials?
Another contractor has proposed 1 inch of closed-cell foam and filling the rest with blown dense pack fiberglass. No one that I’ve talked to wants anything to do with cellulose. Maybe it’s a west coast thing.
Your opinions are greatly appreciated.
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