Snow On Your Roof…Do You Treat the Symptom or the Cause?
Snow build-up and icicles can damage your roof. Proper air-sealing and insulation can help avoid this problem. Photo credit allstate.com
By Bob Tortorice
Believe it or not, snow build-up on your roof is caused by the lack of heat escaping to it, in a manner similar to what happens with an unheated garage or a well-insulated house.
In the past, houses didn’t have much insulation, oil was cheap and heating with firewood was common. The heat reached the attic and melted the snow off the roof. Even now, almost anywhere, you can still see many roofs with little or no snow indicating a lack of insulation.
Snow on the roof of an unheated and uninsulated garage is typically melted by the sun, and not by heat escaping through the roof. A well-insulated house sees its built-up snow melt for reasons other than escaping heat. A particular kind of problem house is the one that is poorly insulated, but where lost heat from the building is not enough to clear the volumes of snow delivered by Mother Nature in our typical winters. The heat only melts the bottom layer of snow creating heavy water- and ice-laden snow conditions. The result is significant icicles, damage to roofing materials, or worse yet, structural roof failure, when the roof collapses under the weight of the snow and ice.
What should you, the homeowner, do? Today, you may have to treat the symptoms of problems and remove the snow by shoveling it off the roof. Tomorrow — meaning spring or summer — you have a chance to treat the fundamental cause by properly insulating both the attic and the basement. Those basement walls have no insulation and the exterior walls are generally poorly insulated, and may have open gaps and holes dating from construction or due to other causes, creating open pathways for heat to find its way into and through to the poorly insulated attic, causing ice dams and very large icicles.
A word of caution: beware the roof of a newly air-sealed and insulated house that was not designed for today’s snow loads. Thirty plus years ago, roofs were designed for 30 to 40 pounds per square foot of snow load. Today’s roofs are designed for snow loads between 65 to 110 lbs. If you decide to insulate your home later this year, it is essential to confirm that your roof is able to handle heavier snow loads. Just adding insulation to the attic floor is not enough, nor even the best first step. Heat loss is also caused by airflow of heated air, in the house’s framing, structure, and finishes, or “shell.” A principal means of airflow is through gaps, holes, and passages. Forty percent of a home’s heat loss is through infiltration, which causes many of the drafts you feel every day. The attic and basement must be air-sealed before any insulation is added, using a variety of approaches and methods, most of which are basic, and many of which can be done by handy homeowners.
The sequence is (1) snow on the roof, (2) building heat loss causes icicles, (3) icicles create ice dams, and (4) ice dams cause the back up of water that leaks into your attic and home causing major damage. Treating the symptom by removing the snow doesn’t treat the cause at all. It’s a temporary fix, which will be repeated year after year, snowstorm after snowstorm. If this is what you experience this winter, take the spring and summer to hire an energy auditor to investigate and treat the cause so that you can enjoy the rest of this winter and future winters without the worry of ice and water backups into your home. And you’ll be warmer, too!
Bob Tortorice has over 30 years of green building experience. He is the owner of Building Alternatives, Inc. and Alternative Energy Audits in Franconia. Call 823-5100 or visit www.buildingalternatives.com or www.epsbuildings.com to learn more about “Building Life Long Savings.”
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