BOSTON (CBS) — Heavy snow buildup can not only cause dangerous conditions on roadways, but can also cause potentially hazardous ice dams on building rooftops.

Ice dams occur when large amounts of snow on the roof  melts off and freezes on the gutters, causing water on the roof to pool above the ice.

WBZ-TV’s Jonathan Elias spoke with General Contractor of PBS’ “This Old House” David Silva in February 2011 about how to keep homes safe from dangerous ice dams that can form on roofs.

One danger of ice dams is the bearing weight, which can cause the roof to collapse.

“There is a lot of load,” Silva said. “Obviously the steeper the [roof] pitch the better off you are, but the lower the pitch you should be concerned.”

“Get some of the weight off your roof,” he said.

The pooling water on top of the dam can seep through the shingles and cause a leaky roof.

“Your shingles are meant to repel water this way and as the reservoir grows it goes up the shingles gets to the top of the shingle and gets inside your house,” Silva explained.

“Clearing the whole roof of snow is the best way to prevent ice dams from forming,” Silva said.

“If you’re going to take the snow load off the roof then take it off the entire roof,” he said.

However, Silva cautioned an added danger for homeowners is clearing off snowy rooftops.

“Don’t go up on the roof if you can help it,” Silva said.

There are products that can be thrown onto your roof to break apart an ice dam. Products like calcium chloride pucks, potassium chloride pellets and chlorine can all be used to melt snow and break apart ice dams without doing any damage to your roof. These products can be purchased at most home and hardware stores.

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