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Five Reasons Ice Dams Occur

23 January 2020

Present weather conditions have created the perfect environment for ice dams to form on homes in the Twin Cities and Western Wisconsin.  Ice dams prove problematic because it’s often only a matter of time before the sheet of ice that’s formed on a roof’s edge backs up onto the roof, beneath the shingles, into the soffits and finally into the home’s interior.  Ice dams that get attic insulation wet, prevent the material from working as it should, while also contributing to mold growth.  At times, ice dams can also damage a home’s drywall, causing the need for replacement.  While roof heat cables, salt pucks, and roof steaming can provide temporary relief, they do not address the underlying reasons ice dams form.  If your home has ice dams, here are the top five reasons they’re likely occurring.

Lack of Attic Air Sealing:  Attic air sealing is the thorough process of identifying open crevices in an attic that are allowing hot air to exit the home, creating ice dams.  Vulnerable spots for that often require attic air sealing to include the area surrounding the attic access door, older recessed lights, and roof penetrations.

insulation and ventilation

Inadequate Attic Insulation: The measurement used to determine the effectiveness of a home’s insulation is known as the R-value. The higher the R-value, the more energy efficient it is.  In the Twin Cities and Western Wisconsin, it is best practice that the minimum level of insulation an attic has is R-50.  This approach prevents warm air from rising into the attic space and escaping, creating liquid water which refreezes when it reaches the cold roof edge, creating an ice dam.  It’s worth noting that certain types of insulation can settle over time, causing the need for additional insulation to be installed.

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Shoddy Chimney Flashing: Metal chimney flashing works to divert water away from the chimney and prevent it from penetrating your roof and its underlayment.  In our harsh climate, chimneys repeatedly encounter snow, ice and heavy winds.  This can cause the flashing to crack and break away from the roof.  When this occurs, it provides the opportunity for the home’s hot interior air to leak out.  In addition, water can also penetrate the chimney.

Deficient Roof Ventilation: During the winter, warm air from the home’s lower levels can rise to the attic.  Without proper levels of roof ventilation underneath the roof deck to release this heat, the attic will heat up to a level that will cause water on the roof to melt and then re-freeze when it meets the roof edge.  Reliable insulation and ventilation contractors should be able to easily explain the difference between ridge, soffit, and gable vents and discuss which should be used for your unique situation to encourage proper levels of insulation.

Ridge Vent

Misdirected Interior Exhaust Fans: There are no scenarios where interior exhaust fans, such as those found in your kitchen or attic, should blow air into the attic.  When this warm humid air reaches the attic, it raises the space’s temperature, creating an ideal environment for ice dams to form.  Even more frustrating is the fact that excess attic moisture can damage the attic insulation and lead to mold growth.

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