Ice Damming 101

22 Feb

Ice Damming Formation and Solution

Ridges of ice form along the eaves of houses, causing millions of dollars of structural damage every year. Water-stained ceilings, dislodged roof shingles, sagging gutters, peeling paint, and damaged plaster--all are the familiar results of ice dams.

What is ice damming?

An ice dam is a block of ice that forms along the eaves of the roof after a heavy snowfall. Ice damming occurs when warm air leaks from the house and causes snow on the roof to melt. As the snow melts and trickles down to the edge of the roof, it often refreezes again along the cooler overhang. Every inch of snow that accumulates on the roof insulates the roof a little more, causing more warm air to be trapped inside which also causes more snow to melt and refreeze. Heavy snow and frigid temperatures produce the most significant ice dams, as you may have noticed after our recent snow storms!

What happens when ice dams form?

The real damage occurs when ice dams prevent melting snow from draining off the roof, causing it to back up under roof shingles and leak into the house. When water leaks onto attic insulation, it becomes less effective, allows more ice dams to form, leading to more leaks. A vicious cycle. When the water leaks into the walls, the insulation begins to sag and leaves a void at the top of the wall, again reducing your heating efficiency. When moisture becomes trapped in the wall cavity, mold begins to form and overtime it will eat away at framing materials and metal fasteners and wreak havoc on allergy sufferers. Trapped moisture can also cause paint and siding to peel and crack long after the ice dams have disappeared.

How do you prevent ice damming?

In this case, prevention is the best cure. Keeping the  surface of the roof cold prevents the cycle of melting and freezing that causes ice dams in the first place. Proper air sealing, insulation, and attic venting are the best way to eliminate the problem.

For a quick fix, fill a leg of pantyhose with a calcium chloride ice melter and lay it onto the roof so it crosses the ice dam and overhangs the gutter. The calcium chloride will eventually melt through the snow and ice and create a channel for water to flow down into the gutters or off the roof. DO NOT USE ROCK SALT… it will stain the roof and siding!

Heat tape and heat cables have also been used to alleviate damming, but often cannot compete with the sheer volume of snow and ice and can cause further damage by making roof shingles brittle. Snow rakes may help remove ice dams and snow along the eaves, but again, take care not to damage the roof or yourself!

If ice dams do occur and your roof starts leaking, take appropriate action to minimize the damage. Need some help with the repairs? We know some guys...

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