Ice Dams: Getting to the Root of the Issue

by ‐ Tags: alternative energy, building science

With winter storm season in full swing, it's a good time to think about dealing with recurring and damaging ice dams.  Ice damming is a common issue for multifamily building owners in colder climates, especially in regions that have older building stock. But ice dams are a preventable and solvable problem.

Ice dam View image at Wikipedia

Chronic ice dams can ruin your building by damaging shingles and gutters. In an area like Boston, which receives about 43 inches of snowfall annually, all that snow often ends up at the edge of your roof as a mountain. Severe cases of damming can cause building leaks that lead to deterioration, mold, and expensive repairs (not to mention the dangers from falling ice!)

The good news is that ice dams are a solvable problem. The even better news is that properly solving your ice dam problem will lead to lower energy costs and a more comfortable building.  Common ice dam fixes focus on getting rid of snow and ice by raking the lower portion of roofs, chipping away ice that has already formed, or installing heated coils along the roof edge.  Unfortunately, these fixes are only band-aids and don’t get to the root of the problem.

Ice damming is primarily caused by heat loss in buildings. The lost heat melts snow, which then refreezes at the roof edge forming the ice dam. The solution is to keep the roof deck cold in order to prevent this chronic melting. 

Excessive heat loss is commonly caused by three factors: 

In a best case scenario, heating systems should not be located in an unconditioned attic space.  The system will operate more efficiently and heat from the system will not contribute to ice dams if it is located in a conditioned space.  This is true for the heating equipment as well as the ductwork, which is best maintained in a conditioned space.  If you can’t remove the ductwork from the unconditioned attic, make sure that the ducts are properly sealed to prevent leaks and well insulated to prevent conductive heat losses to the attic. 

To address conductive and air leakage heat losses, establish a thermal barrier that meets or exceeds the current building code for your jurisdiction and include an air barrier that stops warm air from escaping the thermal envelope.  This can be done on the attic floor with air sealing and installation of additional insulation, or it can be done on the roof surface with an air-impermeable insulation. 

Lastly, if you have a vented attic make sure that you have adequate ventilation area and that the ventilation is not blocked.  A properly vented attic keeps the roof surface cold to avoid ice dams, and will vent unwanted moisture to prevent building rot and mold build-up.

And keep this in mind as you work to prevent ice damming: attic insulation improvements are one of the most effective home improvement projects with respect to ROI. Some can pay for themselves in as few as two years! Check out this post for some great tips on green attic insulation.

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