I’ve recently purchased a 1980 vacation cottage near a lake, 1200 sq. ft. main floor, finished basement, propane and whole house A/C with ducts between floors. 6×12″ beams, 8′ apart, with support through to the basement floor every 12′. The ceiling throughout is T-111 siding throughout. Above that are 2×8″ rafters. Between the rafters is a product I haven’t seen before: 1″ of what seems to be cellulose board, bonded to 1″ of what seems to be isocyanurate foam, glued to 6″ of fiberglass, with kraft paper on top of that. As best as I can tell, this came as a complete system. Above that is sheathing. There is no vapor barrier between the ceiling and the insulation. I don’t know what the original roofing was, but it leaked, and there are stains on the T-111 in places, and it’s clear that at some point water ran down the T-111 in places and ran out at the low point in the roof. The owners had roll roofing installed–perhaps over whatever was on the roof already–I don’t know. (The slope of the roof is barely 2 in 12.)

When I bought the house, I was bothered by a sort of wet wood smell, but the home inspector doesn’t think it’s rot. I removed the 29 year old carpets and pads, which helped, and ventilation and air conditioning have helped some. I think that the house sat uncompleted for a winter with the floor deck on it, as it’s clear that water has run down between the joints in the plywood flooring and down the joists. But no real rotting. A few sheets of plywood are black underneath. The inspector said I should spray on a 2% solution of bleach and water to kill any mold, then paint the underside of the plywood and the joists with a paint with mildewcide in it (should I?).

I removed a sheet of the T-111 ceiling in the bedroom where the smell is the worst. Apart from some rusty nails and some rot on the edges of the T-111 in the worst spot where the water ran out, I didn’t see any rot. But the insulation seemed damp. When I reached up into the fiberglass, it was very humid. The sheathing above it seemed solid. Remember, there is NO ventilation in this roof, and the fiberglass and kraft paper are against the sheathing. After a few days, the exposed insulation seemed nice and dry. And the smell is decreasing.

What should I do? How do I dry out the humidity in the insulation? I had thought that perhaps I should cut slots or holes in the sheathing and kraft paper to allow for ventilation, then install a cold roof above it by nailing 2x2s to the rafters through the sheathing, nailing on new sheathing, then an inch of foam, followed by EPDM roofing. This would let moisture escape, but I’ve read that this could cause a problem by letting it condense on the bottom of the cold roof. Plus, it’s pretty expensive. I’ve read recently that warm roofs are the new requirement for cathedral ceilings (the ceilings in this simple house run from 7′ to 10′). But they also require carefully maintained vapor barriers, and that’s not easy for me to achieve with unpainted T-111 and a ceiling with structural beams.

Please help! I would just as soon do this right, rather than adding to the problem.