Do unvented cathedral plank ceilings require spray foam?
I am designing the envelope of a 600 sq. ft. house to be built later this year. It has a cathedral ceiling with a few irregularities that would prevent proper venting. I was planning to use cellulose between the rafter bays, insulate on top of the roof sheathing with rigid insulation, and use the airtight drywall approach to keep interior house moisture out of the cellulose. However, my wife and I want to build the house in a cottage style with wood planks on the walls and ceiling. If I cover the drywall with planks, I have added lots of holes which worries me that moist air is going to enter the cellulose. Does this mean that to avoid moisture issues, I must use spray foam instead of cellulose?
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