What causes ice dams and what can be done to prevent them?
An ice dam is a condition formed when ice builds up in gutters, explains Tom Leitheiser, manager of the Siding Division of J & B Construction in Milwaukee. The process is triggered by excessive heat in the attic, when the heat warms the roof deck and causes the rooftop snow to melt. The slushy, melted snow flows into the gutters, where the slush freezes, because the gutters are away from the escaping heat and remain cold. As the process continues, the ice gets thicker, forming a dam. Eventually, water will “pond” behind the ice and may leak through an asphalt shingle roof. “Roof shingles are designed to shed water, but will not resist ponding water,” Leitheiser said. “The leaks will occur just above the ice dams, penetrating the overhangs.” Leitheiser suggests keeping the attic cool with good ventilation and adequate insulation. “The attic should have about R-40 or about 15 inches of insulation. Close all air leaks into the attic and insulate and seal all access doors.” He also suggest
