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Your Tewksbury Today

Beware Of Ice Dams Forming On Your Roof

Dec 26, 2017 05:44AM ● By Rick Spencer

Large icicles along the edge of your roof are a telltale sign of ice dam build-up.

I’ve got a funny feeling that a lot of people around town are going to be using the word “Dam” a lot over the next few weeks, even if they’re not the type of person who goes in for using a lot of profanity.

The “dams” I’m talking about are ice dams, and the bad news is that they’re probably forming on the roof of your house even as you read this.


Ice dams form on the roof or your house when we get a combination of a lot of snow and very cold temperatures – just like the weather we’ve had in New England over the past two weeks. Ice dams are caused when the heat from your home warms the underside of your roof, and causes the layer of snow closest to the roof to melt.

Once the snow that’s closest to the roof melts, the water runs down your roof (under a big blanket of snow) and most of it runs into your gutters or drips off and falls harmlessly to the ground. But when the air temperature is below freezing, this run-off water can refreeze along the edges of your roof, causing ice to build up near the edge of your roof.

The ice usually builds up over the overhanging part of your roof known as the soffit vents. These vents are installed in an effort to keep air circulating through your attic all year round. In the summer, this keeps your house cooler and saves you money on air conditioning.

In the winter, proper soffit ventilation is supposed to help prevent ice dams from forming by keeping the underside of the roof cold, so the snow cover evaporates from the top instead of melting from the bottom. But if your house isn’t well-insulated and too much heat is escaping into your attic, then the soffit vents become your enemy, not your friend. Snow melts over the warmer, upper parts of your roof and then the melted snow (i.e. water) trickles down your roof and refreezes when it hits the cold edges of your roof over the soffit vents.

Large icicles hanging from the edge of your roof are often a sign of ice dams forming.

Once a layer of ice forms along the edges of your roof, water starts to back up behind it, and eventually that water seeps under your shingles and into your attic and walls (see the diagram). Water damage from ice dams can be extensive and costly. It gets down inside your walls and destroys your insulation. It can destroy ceilings, and leak out around window sills and door openings.

Fortunately, your homeowners insurance often covers the cost of repairing damage caused by ice dams. But that doesn’t prevent the hassle and annoyance of having water dripping into your house in the middle of the winter, or having work crews come in and rip apart your home so they can fix all the areas that the water has ruined.


There are several ways to treat ice dams once they form:

  • Apply a calcium chloride form of ice melt to the edges of your roof in order to melt the ice dam and let the water flow freely off your roof. You don’t need to melt all the ice off the edges – just cutting a few channels in the ice will solve the problem, because water always seeks the path of least resistance.
  • Try to avoid using rock salt to melt the ice dams. The more expensive kind of “ice melt” is calcium chloride, while rock salt is actually sodium chloride. Rock salt can damage your roof shingles and the landscaping plants most people have around their houses. Calcium chloride is safer for roofs, people and pets.
  • One way to save money and avoid re-applications of calcium chloride is to fill a porous cloth tube (and old pair of panty hose works well) and just lay that along the edge of the roof, in a somewhat serpentine fashion, if possible. This will gradually melt holes in the ice dam and let the water flow through.
  • Never use a hatchet or an axe to chop through the ice to remove it -- you may break up the ice but you'll probably rip off a bunch of shingles or ruin your gutters while you are at it.
  • Always be careful when working with ladders in wintry conditions. A ladder placed on an icy surface can create a dangerous situation. If you’re not handy, consider hiring a professional. Most roofing companies or gutter installation/cleaning companies are skilled at removing ice dams, and the minor expenditure of paying for this service is usually well worth it. Just make sure they have insurance before you let them near your roof.


There are two ways to prevent ice dams from forming. The first is to upgrade your attic and roof insulation to proper levels. Upgrading the insulation in your attic floor and around the opening to your attic (especially if you have a pull-down ladder) is a wise investment because not only will this help prevent ice dams, but it will also lower your utility bills year-round, by preventing warm air from escaping into your attic in the winter and cool, air-conditioned air from escaping into your attic in the summer.

Upgrading the insulation on the underside of your roof keeps snow from melting on the underside and will help prevent ice dams.

The other way to prevent ice dams is to install an ice dam heating cable that you can buy from the home improvement store for somewhere between $50 and $100. This cable is installed along the edge of your roof, before the first snow falls, and then it is plugged into an electrical outlet. The electric current warms the cable, which in turn melts the ice before a dam can form, and gives the water from the melting snow a clear path to run off your roof.

You can install these cables after an ice dam has formed, but they work better when permanently installed before winter hits, when the roof is clear of snow and temperatures are well above freezing.




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