owens corning diagram of ice dam on roof
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.


How do you prevent an ice dam?
Keeping a consistent attic temperature can help prevent ice dams. Insulation and ventilation are key components of maintaining the proper conditions in the attic and on the roof deck.
Proper use of Ice & Water Barrier Products, plus insulation and ventilation, help prevent ice dams – a major culprit when it comes to roof leaks.

Proactive Tip: Bring in the Trusted Experts. Call a local expert who can evaluate your roof for damage and determine what your roof needs are. This could include additional shingles, underlayments, ice and water barrier products, ventilation and/or additional insulation.