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Hello – New to the forum and looking for some guidance on a ventilation issue. In the process of hiring a roofing contractor to replace roof on 100+ year old farmhouse. Located in north eastern lower Michigan, climate zone 6A. Second story was renovated a few years ago down to the studs, open cell spray foam applied to exterior walls. Each of the rooms upstairs has an area (about 3 ft in length diagonal) where the roof line intersects the wall and ceiling. These areas were spray foamed in addition to the exterior wall section below it.
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Existing shingles are about 30 years old, and roof currently has about eight metal ventilation ”cans”, closed soffits, and roof framing is true 2 x 4’s 16 inch on center. Ventilation Rafter Baffles were not installed prior to foam. Ice dams occur in winter. Roofer offered to replace can vents with ridge vent. Will be removing masonry chimney and air sealing attic floor.
Wondering about any way to increase roof underside ventilation short of removing insulation behind new drywall and installing soffit vents? Thanks!
 

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With all that foam against the underside of the roof, laying sleepers on the existing roof deck and sheathing that is about the only way to get proper ventilation. IMO people that foam against roof sheathing should be shot, unless enough r value is there to eliminate any condensation problems. Every single roof I've worked on that had insulation tight against the roof sheathing had rot or at least evidence water damage on the sheathing.
 
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