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Excessive weight of heavy snow and ice dams can impair any roof, no matter how old. There can be severe damage to a home's roof and gutters. Water can seep between shingles and drain inside your home, damaging interior ceilings and walls. If ignored, accumulated snow and ice on a roof can cause thousands of dollars in both exterior and interior repairs.
An ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow (water) from draining off. The water that backs up behind the dam can infiltrate a home's interior and cause damage to walls, ceilings, insulation, and other areas.
Following photo and content from the University of Minnesota Extension
Cross-section drawing of house roof with ice dam showing water damage.
Listed below are highlights from the University of Minnesota Extension, the authors Patrick Huelman, Extension specialist; Richard Stone, Extension educator; Timothy Larson and Lewis Hendricks
Nonuniform roof surface temperatures lead to ice dams.
Heat loss from a house, snow cover and outside temperatures interact to form ice dams. For ice dams to form there must be snow on the roof and, at the same time, higher portions of the roof's outside surface must be above 32 degrees F (freezing) while lower surfaces are below 32F. These are average temperatures over sustained periods of time. For a portion of the roof to be below freezing, outside temperatures must also be below freezing.
The snow on a roof surface that is above freezing will melt. As water flows down the roof, it reaches the portion of the roof that is below 32F and freezes. This causes the ice dam.
The dam grows as it is fed by the melting snow above it, but it will limit itself to the portions of the roof that average below 32F. So the water above backs up behind the ice dam and remains a liquid. This water finds cracks and openings in the exterior roof covering and flows into the attic space. From the attic it could flow into exterior walls or through the ceiling insulation and stain the ceiling finish.
Since most ice dams form at the edge of the roof, there must be a heat source warming the roof elsewhere. This heat primarily comes from the house. In rare instances, increased heat from the sun may cause these temperature differences.
Treat the ice with a suitable ice melt chemical* and use appropriate tools to break ice into chunks, or have the roof professionally steamed to remove the ice buildup.
*Calcium chloride, the product used to melt ice from sidewalks and driveways, works well.
Fill a tube sock or pantyhose with the granules, tie the ends closed, position the socks vertically over the dam, and have the socks hang slightly over the roof edge. The melting will occur towards the center, through and down the dam, allowing the water to flow off the roof.
Regular care and maintenance are the keys to preventing ice dams before they occur.
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