Ice dams are one of those winter problems that can feel unfair: you didn’t do anything “wrong,” but your roof can still end up leaking. Here’s the simple version: ice dams form when snow on the roof melts, runs down to a colder edge, and refreezes—creating a dam that traps water. Once water backs up, it can slip under shingles and find its way into ceilings, walls, insulation, and trim. This guide explains what causes ice dams, what actually prevents them (and what doesn’t), and how to reduce the chance of a winter water claim. Quick answer: what prevents ice dams? Ice dams are prevented by keeping your roof surface closer to a consistent cold temperature so snow doesn’t melt unevenly. In practice, that usually means: Air-sealing the attic (stopping warm air leaks from the house) Insulating properly (keeping heat in your living space) Ventilating the attic (moving cold air through) Managing roof-edge conditions (gutters, drainage, snow load) Roof rakes and heat cables can help in certain situations, but they’re usually “symptom management,” not the root fix. What is an ice dam (in plain English)? An ice dam is a ridge of ice that forms along the edge of a roof. When it blocks melting snow from draining off the roof, water can pool behind it. That trapped water may: seep under shingles enter through nail holes soak insulation stain ceilings and walls contribute to mold or rot over time Ice dams aren’t always obvious until you see one of these signs. Signs you may have an ice dam (or are heading toward one) Look for: Icicles forming along the eaves (not proof by itself, but a clue) A thick ridge of ice at the roof edge Water stains on ceilings or exterior walls Bubbling paint or damp drywall near exterior walls Dripping behind gutters Uneven snow melt (bare roof patches above warm areas) If you see interior staining, treat it as an urgent issue. Winter water damage often spreads farther than it looks.