Many homeowners in Wisconsin are familiar with the problems associated with ice dams, but don’t understand why they form or what can be done to prevent them.
Ice dams form when snow on a warm sloped roof melts and flows down the roof, until it reaches below freezing temperatures, typically at the eaves. There it freezes, forming a dam, and snow that melts later cannot drain properly through the dam. The water that backs up behind the ice dam can leak into the home and cause damage to ceilings, walls and floors.
Ice dams occur when a temperature difference of about 10 degrees F or more exists on your roof sheathing, enabling a thaw-freeze process. Ice dams are also most likely to occur when the outside ambient temperature is 22 degrees F or slightly colder.
The most common cause for ice dams is heat loss due to improper insulation and/or attic ventilation. Inadequate attic insulation, poor ventilation and air leakage are some examples.
The best way to stop ice dams from forming is to keep the entire roof cold. In most homes this means blocking all air leaks into to the attic from the living space below and increasing the thickness of the attic insulation.
Adequate roof ventilation is also key and it is important to ensure the roof ventilation is balanced. This means that for every inch of air exhausted, the amount of air intake at the eaves must be the same or greater. If an attic has a properly balanced system, the airflow will move from the bottom of the attic to the top, exhausting heat and moisture.
Preventing ice dams may not be possible at all times, but you can protect your home with simple repairs by following the steps above. Unfortunately, once an ice dam has formed, there is not much that can be safely done to remove it.