Rows of long variable-length icicles hanging off the eaves of homes make up part of the traditional New England scenery and are considered by many to be attractive. The reality is that they are indicators of excessive heat loss and can cause significant damage to a home.
Both old- and new-construction homes are having ice dam problems now that temperatures are at their lowest. While heating systems are generating more heat than any other time of the year as they try to maintain comfortable indoor temperatures, when that heat escapes, ice dams result. Where ice dams occur, water gets backed up under shingles and into roofs and walls.
Common solutions to ice dam problems have traditionally (and mistakenly) been to install aluminum strips of roofing or electric heat tape near the eaves. Many continue to recommend enhanced ventilation in the attic either at the soffit or by installing ridge vents.
The problem is that none of the above proposed solutions address the cause of the problem, which is heat loss into the attic. Air leakage in which heated air passes freely into the attic is the primary reason the attic is well above freezing, thereby causing ice and snow to melt on the roof.
Insufficient or poorly installed insulation is the second main cause. Water runs down the roof to the eaves (which extend past the outside wall) and are below freezing (32 degrees), where it then refreezes, creating an ice dam.
So, if heat tape or ventilation isn't the solution, what is? I suggest that homeowners go into their attics with a thermometer and see what the attic temperature is compared to the outdoors. If your attic is above or near 40 degrees when it is below 32 degrees outside, you will find that it makes good economic sense to air seal and to improve insulation.
The first step to addressing the cause of ice dams is thorough attic air sealing. From one end of the attic to the other, points of air-leakage — such as lighting fixtures, vent fans, wiring holes, duct and chimney chases, hatches, changes in ceiling height and wall top plates among others — should all be sealed. This can be done by the homeowner or performed by a professional. Spray foam, caulking and foam board are materials typically used for air sealing.
Only after completing the task of air sealing is adding insulation in order. Ideally, there is nothing wrong with a goal of insulating your attic to a range of R-50 to R-70 in New England. Blown-in cellulose insulation is a good choice, usually better than fiberglass batt insulation, particularly for attics. Another choice is commercially applied spray-applied foam. It is best to let an expert examine the site and determine the type of insulation needed.
We sealed and insulated an attic to R-50 in half a house in Newburyport just before the snowstorms came a few weeks ago. The owner sent me a picture last week of massive icicles hanging from his neighbor's eaves. There were none on the side where we had just insulated. Now, that's a satisfied customer.
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Tim Gould is director of Energy Egghead (www.EnergyEgghead.com), an Amesbury-based home improvement company that provides thorough energy audit and conservation services.