Impending thaw could create dreaded roof ice dams

Just because your house survived the prolonged arctic temperatures this week doesn't mean you're out of the woods.

The looming thaw expected to result from a weekend entirely above freezing might sound like a welcome change, but it also has the potential to create ice dams on roofs that could result in leaks or other structural damage to a house.

"We're going to have a lot of them," warned Ted McLaughlin of Ace Roofing Services in St. Charles. "The temperature change is going to do a lot of damage to roofs if people don't take care."

After two days of lows below minus 20 degree, temperatures are expected to climb to near 40 on Saturday and stay above freezing until Monday night.

Ice dams are created at the edges of roofs and gutters filled with snow. Snow on the portion of the roof that's over the warm house is likely to melt more quickly than snow on the roof's overhang.

If water from the thawed snow can't run down the roof and into the gutter, it will pool at the edge of the unthawed snow on the roof.

Most roofs can handle running water, but not standing water. Eventually, the pool could warp the wood in the roof and cause leaks or other damage.

"Hopefully because this is expected to be a quick thaw it won't be as bad for most roofs that are pitched," said Chuck Hanson, president of Hanson Roofing in Evanston. "Flat roofs may be more at risk, especially if the snow on the roof is thawing but the drain that would normally carry it off is still frozen."

Both roofers suggested using a roof rake to clear the snow at the edge of the roof.

McLaughlin said filling pantyhose with calcium chloride or road salt and placing it perpendicular to the gutter is also a way to avoid damming.

"It will burn a channel through an ice dam or snow and allow the water to torpedo down into the gutter," he said. "Depending on how big the roof is, you may need more than one."

McLaughlin warned against banging on ice formed on roofs or gutters, saying that could cause damage.

Hanson also suggested sprinkling calcium chloride or road salt into the gutters now to ensure quicker thawing.

"If you've got gutters at two stories or higher, though, call a professional," he said.

Rockford, Mundelein, Barrington break all-time cold records

  Icicles created by an ice dam last February hang from a house in Palatine. With the temperatures climbing in the next few days, ice dams could threaten many suburban homes' roofs. Mark Welsh/, February 2018
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