Ice dams and water damage
Warm air rises into attic through inadequate air sealing and insulation.
Heat causes the upper part of a roof to warm above freezing, melting the snow.
SOURCE: Tribune News Service, Wisconsin State Journal research
Click steps to see how they form and how damage might result
Warm interior
Heat
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Snow melts and water runs down until it reaches an area of the roof that is below 32 degrees and freezes.
Over time the freezing water creates an ice dam.
Warm interior
Heat
Icicles
Once an ice dam is formed, additional water is forced to pool on the roof behind the dam.
Water seeps under the shingles and can cause damage to ceilings, rooms and internal structures.
Warm interior
Above freezing
Below freezing
Icicles
Heat
Ice
dam
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Water
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Check for inadequate attic insulation, poor or blocked attic ventilation or air leaks
from the home to attic.
Ways to prevent ice dams
A short-term fix is to use a snow rake to remove snow from a roof.
Soffit
vent
Ridge vent
Heated electrical wire can be attached to
the lower sections of roof where snow freezes.
Snow
Below freezing
Snow
Ice
dam
Snow
Insulation
Cold air flow
Above freezing
Above freezing