A client of mine is having a water issue in his finished attic. They live in a development in Massachusetts with super-insulated houses. The houses have a “hot roof” assembly with no ventilation. The roof consists of asphalt shingles, tar paper, 5/8 ply sheathing, 14″ tall I-joist rafters at 24″ oc, dense pack cellulose, fabric to hold the cellulose insulation and finally a polyethylene vapor barrier stapled to the bottom of the rafters. The main space is finished and the collar ties are only encasing an area about 4′ wide by 3′ tall (12/12 pitch) with drywall ceiling. My client (and another neighbor in this development) got air conditioners to cool their attic space during the summer. During hot and especially humid summer days water is condensing on the back side of the polyethylene and soaking the insulation. I’ve stuck my hand up into the insulation during one of these events and it is damp right up to the peak of the roof. I think some of the water probably heats up enough to become vapor again as it nears the roof but hits the plywood and asphalt paper allowing minimal evaporation. I’m guessing the bulk of the water never even has a chance to get out of the assembly before it cools off in the evening and the water condenses on the back side of the plywood. The water only seems to have a chance to dry out once the hot humid weather passes and the temperature differential evens out.

My client wanted me to install a fan to blow conditioned air into one end of the cavity above the collar ties/ceiling with an exhaust on the other end of the attic but I think this will just exacerbate the problem cooling the polyethylene and causing even more condensation.

I’m at a bit of a loss as to how to fix this issue. More Insulation in the cavity above the ceiling? Remove the vapor barrier? Better air sealing at the drywall? All of the above?
Thanks in advance!