Roof Heating Cables An ice dam is created when snow melts over a warm section of roof, flows down to the cold eave, refreezes and creates a blockage (or dam) which causes future melt runoff to pool and potentially work its way under your shingles and into your home. Water leaking from an ice dam will first show up in the attic. You may see ice forming on the trusses or plywood sheathing. Next is when the water begins to drip through the ceiling into your living space. The be