What Causes Ice Dams to Form on Your Roof

Ice dams are a common winter problem in areas that see a lot of snow or ice. These solid chunks of ice that form at the edge of your roof can cause serious damage to your roof and the interior of your home. Learning what causes ice dams to form can help you prevent them this winter, saving you the hassle and cost of ice dam removal or expensive repair bills from ice dam damage.

Ice dams form when snow on the roof begins to melt and then refreezes into a solid chunk of ice at the edge of the roof, preventing water from properly draining off the roof. Without a drainage path, water can get forced between and underneath the shingles, causing roof damage and leaking into your home. We explore five common causes of these ice formations and how to prevent ice dams to reduce your chances of serious damage.

1. Poor Attic Insulation

The most common cause of ice dams is an attic that’s too warm. When attics aren’t properly insulated, heat from the house escapes to the roof through the attic, melting the snow directly above the attic. When the melted snow travels down the roof toward the roof edge, it then hits a colder section of the roof, often the overhang that’s above open air. The drastic change in temperature causes the water to refreeze at the roof edge, starting the formation of an ice dam.

When an attic is well insulated, the roof above it stays the same temperature as the rest of the roof, ensuring that snow melts at a consistent rate once the entire roof is warm enough to allow the water to travel all the way off the roof without refreezing. If you’re concerned about your home’s insulation, reach out to a local attic insulation company ASAP to get an inspection (it’s definitely worth it).

2. Thick Snow Cover

Believe it or not, snow can act as insulation, keeping the area under the snow warmer than the surface. If your roof has a thick layer of snow, the snow directly touching the surface can begin to melt underneath the solid layer of snow above it. Once that inner layer of snow melts, it will begin to drain off the roof, refreezing when it encounters a colder area and forming an ice dam.

Prevention Tips

After heavy snowfall, use a roof rake or brush to remove as much snow as possible from the roof. A thinner layer of snow is less likely to melt inconsistently or reach a high enough temperature to only partially melt. Only remove snow you can safely reach from the ground with a long-handled tool—climbing an icy ladder onto a snowy roof can be extremely dangerous. If your roof is particularly high or steep, hire a local roof cleaning company that specializes in roofs.

3. Warm Days and Cold Nights

Sometimes, the only thing to blame for ice dam formation is Mother Nature. When daytime temperatures rise above freezing, and direct sunlight hits the roof, snow will begin to melt. Once the sun goes down, temperatures quickly drop again, causing the melted snow to refreeze before it drains. 

Prevention Tips

While you can’t control the weather, you can try to help melted snow drain quickly when daytime temperatures rise. Keep the roof edge and gutters clear so melting snow can easily make its way off the roof. Consider installing roof heating cables to keep the roof edge and gutters warm enough to allow drainage.

4. Clogged Gutters

While ice dams can form on houses with or without gutters, gutters clogged with ice or other debris can aid in ice dam formation. Gutters themselves don’t cause ice dams, but clear, properly functioning gutters can help lessen the risk of them forming. 

Prevention Tips

Before the snowy season starts, clear your gutters of leaves and other debris. Gutter heat cables can help prevent ice from forming when installed and used properly. If you notice ice forming in the gutters, try pouring boiling water to break up ice or manually removing smaller chunks of ice to allow for unobstructed water flow. 

The best time to ensure your gutters are clear is before you start to see signs of ice dams forming. If you already have ice dams, hire a pro who removes ice dams to clear them out and prevent damage.

5. Ventilation Equipment

Areas around exhaust ducts, chimneys, and other ventilation equipment may get warmer than the surrounding roof, causing snow to melt faster, travel down the roof, and refreeze into the beginning of an ice dam. Because these areas are relatively small, the likelihood of ice dam formation is lower than that of a poorly insulated large space like an attic, but it’s still a possibility.

Prevention Tips

Ensure that ventilation equipment on the roof is properly installed and insulated to prevent heat transfer to surrounding snow.