Four things are required for an ice dams to form:
- Heat loss in your home
- Below freezing temperatures
- Poor attic circulation
Why it happens: Snow melts on the roof from heat loss in the home and ice forms on the roof. Imagine an icicle; water drips and freezes repeatedly and then gradually grows. The same happens on a home, the snow melts from heat loss and runs down the roof until it hits the outer portion of the roof that is the ambient outside temperature. The water freezes. It creates a band along the colder roof perimeter or an “ice dam”. Water pooling and freezing against the dam allows the ice to defy gravity. It will work its way up the roof getting beneath roof coverings and causing damage and leaks all along the way.
What to do.
Be proactive and attack the source of the problem: heat loss and lack of circulation. The warm air escapes and heats parts of the home not meant to be heated: the attic and roof deck. Proper insulating stops heat loss. Most homes are designed to have a cold attic. Proper attic ventilation keeps a cold attic cold. A working ventilation uses the soffit or eaves as the intake and roof/gable vents as the exhaust. This works in the summer to remove heat buildup and in the winter it can prevent ice dams with the same circulation. Heat loss is circulated throughout, exhausted and not allowed to accumulate and heat "spots" causing dams.
- Vent knee wall attics
- Insulate per Minnesota Code at R-49 or 14"
- Cold attics are meant to be the same as outside temperature
- Make sure your attic ventilation works right. More vents does not equal better. Eave and soffit intake must be greater than exhaust, otherwise venting will reverse or cross ventilate. Roof vents exchange air with each other rather than exchanging air from eave to attic ceiling.