After a winter snow storm, some roofs look like a frozen waterfall, as snow on top melts and then refreezes when temperatures drop at night. Such so-called ice dams may look impressive, but they can also do major damage to the eaves of the roof as well as gutters and shingles and the interior of the home.
Ice dams on the roof plague many houses during winter. An ice dam triggers damaging water leakage into the attic and even down through the ceiling into living spaces below. Common sense might suggest that ice dams on the roof result solely from severe cold. Actually, they usually happen because of a partially warmed roof.
Ice dams prevent your roof from draining properly. Water leaks, mold problems and structural damage can all result, and repair costs can be high. An ice dam occurs when warm air in your attic radiates upward, melting snow on the roof. When the resulting water reaches the bottom of the roof, which is much colder because of less heat in the thin section of underlying attic, it refreezes, resulting in a dam that forces additional melted snow to pool up behind it. That standing water eventually finds its way down into your attic and living spaces.