With the onset of another winter just a few months away, Jake Rabe is looking for suggestions on how to prevent the recurrence of ice dams on his older Ontario home.
“Each winter I have to deal with ice damming along two sides of the roof — nowhere else,” he writes in a Q&A post at Green Building Advisor. “The areas in question are a low-slope roof (3/12 pitch, east and west side of the ridge) and a cathedral style roof (8/12 pitch)… My goal is to stop the ice damming.”
Rabe believes that the house was built between the 1920s and the 1950s. Access to the cramped attic beneath the east and west low-slope roofs is through a tiny hatch on the upper floor of the house. Rabe estimates that there is only about 36 inches from the ridge to the attic floor, with the space now filled with a mix of old and new cellulose insulation roughly 12 inches thick. He has no idea whether the insulation is evenly distributed across the attic floor.
Soffit vents have been installed, although he suspects they have been obstructed by wood or cellulose. There are two exhaust vents at the top of the roof. The roof has board sheathing rather than OSB or plywood.
Rabe has solicited suggestions on how to resolve the problem from several roofing companies. They seem to run the gamut: opening all soffit vents and adding fluffy insulation between rafters; removing shingles and installing metal roofing; adding a new roof deck on top of the existing deck and building in an air gap between the two; removing all existing attic insulation before air-sealing the attic floor and blowing in new insulation; and, finally, removing the existing low-slope and cathedral roofs and replacing them with a new roof of a…