Ice Dams – Why Some Houses Get them and Others Don’t

Over the past few weeks weeks it has been troubling to see (and hear) neighbors chipping away at ice dams on their roofs. It’s the talk of the block; water leaks, gutters breaking, ceiling damage…all because of large amounts of ice that have accumulated along the eaves and overhangs of people’s homes. However, the home pictured here has everyone impressed because while others are raking their roofs this home has neither an icicle nor an ice dam. Why not?

Let’s start by reviewing why and how ice dams are formed. Heat rising from the attic will melt the snow resting on the roof, and water will roll down the slope and begin to pool at the eaves. Since the eaves are cooler, usually below 32 degrees, the water freezes in this area. As the water melts, drips and refreezes it creates layers of ice that form a dam, which blocks the normal runoff of water. (See the diagram by UMN) 

The main reason the snow melts and freezes in this way is due to a warm attic and air leakage. Building scientists have been preaching about better air sealing and weatherization practices in homes for years. You want the warm air to stay in the living areas, not rise and leak into the attic. You also want to properly ventilate and insulate to keep the air temperature in the attic and roof cool and even. 

This 2-year-old home is proof of how a properly designed and built home will not have air leaks and heat loss.  The builder of this home brought in Priority Energy to 1) design the heating, cooling and ventilation system and 2) verify air sealing, insulation levels, and air tightness throughout the building process. We see here one example of how the combination of accurate design and testing ensures a durable, energy efficient and safe structure.

If your home is prone to ice dams, try to clear the snow from the eaves as soon as you see it accumulating. Consider putting a fan in the attic if there aren’t any vents present as this will help tp keep the attic temperature cool and more even.  Take photos of where the ice dams developed and get an energy auditor to investigate the areas where the damming developed. Ventilation, insulation, and air sealing can prevent the destructive effects of ice dams and will also improve comfort, energy efficiency and indoor air quality.

Priority Energy has worked with the builder of this Glen Ellyn home for many years and has helped them create over fifty high performance homes in the Chicago area. If you are a builder or if you are thinking about building, be sure to get help from a building science firm. If you would like to improve the performance an existing home, an energy audit by a certified energy auditor is a good place to start. .