A sloped asphalt roof is designed to shed water in one direction, down and off the roof.
What is an ice dam?
A ridge of ice that forms at the edge of a roof and prevents melting snow from draining off the roof.
What causes an ice dam?
Ice dams form when indoor heating rises through the ceiling into the attic and warms the roof surface.
How do they form?
Snow on the heated part of the roof melts and flows down until it meets the part of the roof that is below 32 degrees. At that point, the water freezes into an ice dam.
How do ice dams lead to water damage?
Water backs up behind the dam and, as it sits on the roof, works its way under the roof covering and flows into the attic. From there it can seep through insulation, ceilings, walls and other areas where it can cause damage.