Signs your roof is vulnerable to ice damming

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Q: I have a question about attic insulation. I was under the impression that attics should remain ventilated and uninsulated to prevent the buildup of ice dams. Can you clarify? I have a walk-up attic with floorboards. There is insulation under the floorboards, but nowhere else. There are two walls (inverted v-shape) at the two ends of the house, and in between just the slanted roof down to the attic floor. All the wood framing is exposed. There are two circular vents in the roof. Should I insulate the two side walls, but not the roof? Or the roof, too? Or nothing? --Craig N. A: You're actually half right. Ice damming can sometimes be a little difficult to visualize, but the two primary factors that cause it to occur are a lack of insulation and a lack of ventilation. When snow lies on the roof, heat loss from inside the house will melt the underside of the snow layer. The water from the snow melt runs under the snow layer until it reaches the eaves, where there is no long...