Ice dam on roof — San Jose, California

Ice dams form along the roof edge when snow melts from the warm upper roof and refreezes at the cold eaves. The trapped water backs up under shingles, causing leaks into attic spaces, walls, and ceilings. Left untreated, ice dams cause extensive water damage, rotting fascia boards, and mold growth. A roofer can safely remove ice dams, install ice-and-water shield membrane, and improve attic ventilation to prevent recurrence.