How to Fix Ice Dams When Reroofing – GreenBuildingAdvisor

By Chuck Bickford | March 24, 2025

One of the joys of living in a cold climate is that you may get to experience ice dams—a condition where air and heat escaping the house melts snow on the roof. The melted snow runs down the roof and refreezes at the unheated eave, forming a dam. The cycle continues, only as the melt water repeatedly drains down, the ice dam grows toward the roof peak, and the water soon finds its way under the shingles and into the house.

In a recent Q&A, an architect named Noah, posting as “streamcolab,” writes that he has a 1860s Greek Revival home in Climate Zone 6 that needs a new roof and that suffers from “really bad” ice damming. The second floor of his home sits beneath an insulated 8/12 pitch roof. Like many homes with living space beneath the roof, the sloping ceiling transitions to a flat portion at ceiling height—it’s a straight gable, Noah says, with no dormers.

Unfortunately, the roof and ceiling are insulated with vermiculite that contains asbestos. Although Noah recognizes that vermiculite isn’t ideal, he can’t afford to remediate it right now. “When you have a roof that is actively leaking and limited funds, you have to pick and choose your battles,” he writes.

Noah’s primary concern is to “mitigate the ice dams and moisture within the roof assembly and attic.” The problem is that he doesn’t want to ruin the historic lines of the Greek Revival roof trim details by adding layers of insulation above the roof deck, and he doesn’t want to disturb the interior’s plaster ceilings, which he says are in good condition. Ideally, he needs to make the roof waterproof, then air-seal and insulate his attic and roof deck to prevent continued ice dams.