How and Where Ice Dams Form

ice dam

If you’ve ever been tasked with removing an ice dam from your home, you might have wondered how the ice dam formed in the first place.

An ice dam is a ridge of ice that, once formed, blocks snow and moisture from escaping a given area. To form, the dam requires the perfect temperature conditions and a bed of snow. Temperatures at the snow's highest point must reach above freezing (32̊ F), while areas at the base of the snow must be below freezing.

If these conditions exist, the snow in higher area — above 32 F — will begin to melt and run downhill. When it does, this water will then come into contact with the colder snow and turn to ice. This ice then blocks the way for additional melting moisture to escape, making the dam grow larger and larger.

As the dam keeps growing, it will only continue to add ice in areas that are below freezing. Once the water backs up into the region where freezing temperatures are no longer present, that water will search for other places to escape — including into a home.

Where do ice dams most commonly form?

Ice dams require very specific conditions to form successfully. Yet those conditions are usually more common than you may think.

The slanted roofs on many homes are ideal staging areas for ice dams, particularly if the lower half of the roof is shaded by another section of the roof or the home itself.

Temperature conditions inside the home can play a part in ice-dam formation as well. In many cases, the warm air rising to the ceiling inside the home also warms the roof. This heat keeps the higher portion of the roof warm. Meanwhile the lower portion—which is designed to hang away from the house—stays cool. This creates the ideal conditions for an ice dam to form.

Areas of your house that are shaded tend to get more ice dams since the sun isn’t present to melt the damage.

In the next post, learn why ice dams are dangerous for your home and the people in it.

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