An ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow from draining off the roof. Spotting one quickly can help curb the damage to your home.
During periods of freezing and thawing and refreezing, water becomes trapped above the ice and finds its way beneath the shingles causing a leak inside the home. The lower the pitch of the roof, the more likely there is to be this problem.
Ice dams can lift roofing shingles and let water filtrate in. They can also pull gutters off, which can cause structural damage and lead to potential internal flooding. Hanging icicles might indicate ice dam formation.