Snow on a rooftop can lead to ice dams. Learn when and how to remove it.

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a roof rake removes snow from a roof valley

Heavy snowfall can lead to ice dams, and that can lead to water leaking inside your home

When a big snowfall hits, our eyes tend to stay focused on the ground – shoveling sidewalks, moving cars so snowplows can come through, putting down some sand on icy spots. But it’s a good idea to look up, too. Does your roof tend to accumulate snow? Are there deep valleys that trap snow? Does your home have a tendency to form icicles on the roofline? If so, you may need to rake your roof or risk forming ice dams.

Ice dams are a function of a warm roof surface and cool edges, often from inadequate insulation or roof ventilation. Rain gutters can complicate things as well. Ideally, your attic space will be insulated to prevent heat loss from inside the home from escaping through the roof. The underside of a roof should be vented from eave to peak to keep the roof surface cool. In many homes, especially older homes, this isn’t the case.

You can see an ice dam forming above these icicles in the roof valley. The gutter has already filled with refrozen meltwater.

You can see an ice dam forming above these icicles in the roof valley. The gutter has already filled with refrozen meltwater.

How do ice dams form?

When heat escapes through a snowy roof, it melts the snow on top. The meltwater runs down the roof until it reaches the edge, or falls into the rain gutter.  The cooler temperatures here allow the water to refreeze, forming icicles and often what is called an ice dam. An ice dam is a ridge of ice build-up along the roof edge or in the gutter.  Eventually this becomes large enough that the melting water can’t escape over it and begins to back up on the roof surface. This is where things can get ugly.

The standing water behind an ice dam can seep under the roof shingles, where it penetrates into the home. You may see the results indoors in the form of water marks on your ceiling, water filling a light fixture, drips in one of your windows, or sagging plaster or drywall. At this point you have a serious problem.

A diagram depicting the cycle of ice dam formation

How do I get rid of ice dams?

Prevention is the best approach.

Before ice dams happen:

  • Make sure your home is well insulated, and pay attention to the roof ventilation. (our Home Improvement funds can often be used for this type of work.)
  • Use a roof rake to remove snow at least six feet from the eaves, and in any deep valleys.
  • When installing a new roof, ice and water membrane is usually required at least two feet from the edge, and in valleys. Consider extending this further on the roof if you have known trouble spots.
  • Heat tapes are an option for trouble spots. These electric cables will melt channels in the ice and allow water to escape. They can be useful on the lower portion of the roof or in tricky roof valleys.
A roof rake is used to remove snow from a roof valley.

Use a roof rake to remove snow from the roof, targeting the roof edge and any valleys where snow builds up.

After ice dams have formed:

  • If you haven’t already raked the roof, this will help by removing the source of the meltwater. Remove the snow as noted above.
  • Salt can work in varying degrees of success, but can also damage your roof and gardens. If you do this, use calcium chloride, not rock salt. One method is to fill a long sock or pantyhose leg with salt and place on the roof perpendicular to the ice dam. This can melt a channel in the dam to allow water to escape.   Some hardware stores sell puck-shaped chunks of salt designed to be thrown on the roof.  Whether or not these methods work will depend on the size of the ice dam, the amount of snow still on the roof, and the air temperature.
  • Professional ice dam removal with steam is effective, but also expensive. And if you are having this problem, it is likely many other homeowners are too, so pricing tends to surge. The cost can be upwards of $500 per hour. Be sure to get multiple bids for any type of contracted work on your home. (Author’s note: I have had success using hot water and a garden hose to melt through dams on my own home. I turned up my home water heater to its highest setting, connected a long garden hose to my utility sink, and used the garden sprayer to target hot water on the worst areas of ice, melting them away. This took hours to accomplish and in the meantime nobody in the house was allowed to use the hot water, as it was at a dangerously high temperature.)

ALWAYS WORK FROM THE GROUND. DO NOT GO ON YOUR ROOF. DO NOT USE TOOLS SUCH AS HAMMERS OR CHISELS TO BREAK THE ICE – THIS CAN DAMAGE YOUR ROOF.
WHEN USING A RAKE, BE AWARE OF AND STAY AWAY FROM POWER LINES. 

Will insurance help?

Most homeowner policies will cover the cost of repairing damage caused by water infiltration due to ice dams. But very few will pay for ice dam removal or the insulation work that is needed to prevent it from happening again. Be sure to check your policy to know what is covered.

Winter brings many unique maintenance challenges. Learn about protecting pipes from freezing, and what can happen if your plumbing vent freezes shut.

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