Ice Dam
A ridge of ice that forms at the edge of a roof and prevents melting snow from draining properly.
How Ice Dams Form
An ice dam forms when heat escaping from the attic warms the roof deck enough to melt snow on the upper roof, while the eaves — which overhang unheated space — stay below freezing. The meltwater runs down, refreezes at the cold eave, and builds a ridge of ice that dams water behind it. That trapped water has nowhere to go but backward and upward, under the shingles.
Prevention Beats Repair
Ice dams are fundamentally an insulation and ventilation problem, not a roofing material problem — a brand-new roof will still ice-dam over an under-insulated attic. In Fairfield County's typical January freeze-thaw pattern, the fix is usually adding attic insulation to R-49+, sealing air leaks (recessed lights, bath fans, attic hatches) that let warm air escape, and confirming soffit-to-ridge ventilation is unobstructed so the whole roof deck stays at outdoor temperature.