The dangers of ice damming
By Amy Brown-Bowers • Bankrate.com

The noticeable damage is leaking inside, but the invisible and most costly damage occurs between the visible ceiling and the external shingles. Unaddressed, ice damming may lead to structural failures that cost in the tens of thousands of dollars to remedy, says Clarke, not to mention mould and other health problems.

Common causes
There are a few potential causes of ice damming, but probably the most common is improper insulation of the attic.

"If the insulation isn't adequate in that area, then the heat escapes from the heated space in the house through the attic and then heats up that portion of the roof, which causes even more ice," says Brian Daley, president of the Associated Group of Home Inspectors.

Not only does that mean you'll pay more in heating costs, but also in roof damage.

Ice damming can also be caused by great fluctuations in temperature. "If you look at the city of Toronto right now, we've got so much ice on the roof simply because we've had lots of sun but also lots of precipitation and cold weather," Daley says.

The sun causes the snow to melt, which then turns to ice in the cold evenings and nights.

This can quickly become an ice dam if you have damaged eaves troughs or downspouts because the melting snow and moisture can't be carried away effectively from the building. Instead, it builds up at the edge and migrates into the roof structure.

Breaking the dam
Clarke says fixing ice dam problems usually costs less than $2,000, far less than the $5,000 or so it costs to install a new roof on the average home. "It could be something as simple as one handy man in the attic for one hour," he says.