Slow rise foam or dense pack cellulose in roof slope?
Cape Cod style house– i.e., under roof is kneewall, slope, and small collar attic above the flat bedroom ceilings
1925 house in Washington DC area with slate roof on front side of house, asphalt shingles in back. Roof deck is boards, not plywood or OSB. Currently there is a small amount of cellulose on “attic” floor and some poorly installed fiberglass batts on some areas of roof deck in kneewalls.
Plan is to use foam on the interior side of the roof deck – open cell in kneewall and attic space and “slow rise” foam (brand name “Tiger foam”) in the enclosed slopes. Doing so would mean AC ducts and AC air handler would be in conditioned space.
I am wondering about the best way to insulate the slopes. Dense pack was suggested initially but it seemed there was a risk of moisture problems.
Also, the installer says best practice when applying foam when there is slate roof is to place a plastic vent shute between roof rafters to prevent foam from expanding between the roof deck boards and disturbing the slate (the foam would push the shute flush with the deck so no air space). I wonder how this might affect moisture issues.
Any advice would be much appreciated