Vented I-Joist Rafters
I am building a ranch in southern Michigan with 24 foot rafter spans over a cathedral ceiling (4/12 pitch). Originally I was going to place 3 inches of foam on top of an unvented roof, but to simplify the roof and reduce costs I am now planning on using 12 inches of cellulose with a 1.5 inch ventilation gap at the top 2x piece of the I-Joist with cellulose filling the cavity underneath and a vapor barrier between the I-joists and the purlins that the drywall attaches to. The assembly is shown in the attached image. Does any one see any issue with this plan. Is 1.5 inch enough gap to vent the roof?
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