The conditions that allow ice dams to form occur every winter, and to prevent damage from recurring homeowners must be proactive. When temperatures drop into single digits, big and sparkly icicles may form on the edge of a roof. They sure look pretty, but are actually a warning sign of improper roof insulation and/or roof ventilation, along with possibly air leaks in the attic.
When heat rises into a home’s attic, most of the roof is warmed. However, that warmth doesn’t make it to the eaves. As snow on the roof melts, the water freezes on those cold eaves and creates an ice dam. Because the melted water can't drain into the gutter, it backs up under the shingles and will eventually enter the house. The resulting damage can be extensive and quite costly to repair.