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Icicles and Ice Dams: The Real Story

30 December 2010

If you have icicles, you may have ice dams, which can be damaging and costly.  Read this article from the MN Office of Energy Security to get the skinny on ice dams and how to identify them:

They glisten in the sunlight, hanging off the edge of the roof, each frozen drip bringing them a little closer to the ground. But what causes icicles and (other than the danger of falling chunks) can they cause damage to our homes?

Although small icicles at the edge of the roof are usually just a sign of snow melting and refreezing in the winter sun, large icicles or sheets of ice on the roof can indicate a much bigger problem: ice dams. If the ice forms a layer that backs up several feet from the roof edge, damage can occur to shingles, roof sheathing, insulation, and eventually the interior of your house. But contrary to popular belief, most ice dams are not a result of problems with the shingles or the roof deck; the source is usually a little deeper in the attic.

When snow falls on a roof it will not melt until the air or the shingles get above the freezing point. Shingles can be heated by the sun on a warm winter day, but that usually leads to fairly even melting and few icicles. When the roof is heated from below (through the attic) and the melted snow re-freezes when it drips to the unheated eaves, big icicles can form. Repeated melting and re-freezing can create a build up of ice at the edge of the roof, eventually creating an ice dam that will block the melting water, forcing it under the shingles and into your insulation, and maybe into the house itself.

But how does the roof get heated from below? Inadequate insulation, of course, will allow heat to flow easily into the attic, warming the underside of the roof deck. But many homes with ice dams are newer or have sufficient amounts of insulation. So then what is the cause? Usually the culprit is something known as an attic air leak. Where chimneys, wiring, plumbing vents, ductwork, light fixtures, or other penetrations enter the attic from the heated part of the house, warm, moist air can travel into the attic, leading to the heating of the roof deck. Even well-insulated attics can’t stop the thermal flow from air leaks, and even small openings can pump an amazing amount of heat into the attic.

Attic air leaks can not only be identified by the ice dams on the roof surface, they can also sometimes be spotted by wet or frosty areas of insulation or by frost on the underside of the roof. In order to prevent the ice dams (and subsequent damage to roofs, insulation, and interiors) attic air leaks must be sealed completely. This involves locating all potential ceiling penetrations and sealing them with caulking, foam insulation, or other approved methods. Although not usually a technically difficult project, homeowners must be willing to crawl around in their attic, while digging through the insulation. Certain precautions must be followed (breathing masks, goggles, protective clothing) to do the job safely. Most insulation contractors are equipped and experienced to seal attic air leaks, as well. An energy audit that includes an infrared camera scan can pinpoint locations where air is leaking.

It is also important to note that removing snow and ice from your roof can be hazardous to both you and your house. Crawling around on a snowy, icy roof is not advised. Chopping up ice dams or breaking off icicles will probably damage the roof, fascia, or gutters. Heating cables may keep the ice from forming, but they use a lot of energy and can shorten the life of the shingles. A little sidewalk ice salt can speed the melting process, but remember the ice is only a symptom of what really needs to be fixed. If snow and ice needs to be removed, the best method is to hire a contractor to steam it off. This approach is least likely to damage your house—or yourself!

Even though the icicles may be pretty, they probably are a sign of something that needs your attention. And sealing up those attic air leaks can not only save you thousands of dollars in roof and interior repairs, it can save you money on your heat bill, too!

For more information, check out the Office of Energy Security’s Home Envelope Energy Guide or call 800-657-3710 or Twin Cities, 651-296-5175.

:: Minnesota Department of Commerce: Office of Energy Security

One Comment leave one →
  1. Dan permalink
    30 December 2010 4:39 pm

    Your article was good, although incomplete. Another cause of ice dams are from not enough venting in an attic. Some homes either have too much insulation in their attic thus not having room for air to move or there is not enough venting for air to circulate and keep the roof from heating and cooling thus again causing ice dams. An attic should be cold and stay cold, during the winter. You mentioned an Energy Audit in passing but this should be more emphasized. Unless you have the knowledge to discover or find air leaks or the cause of issues in your home, an Energy Auditor should always be a homeowner’s first call. Without knowing exactly what is happening in your home, contractors or people are just guessing and may not fix the problem adequately. With a little money spent on an Energy Audit a homeowner may save by not spending money on fixes that may only fix a symptom and not the real problem. Also, look for an Energy Auditor that is not trying to sell you something. A 3rd party unbiased opinion will explain exactly what is going on with your home without an agenda to sell you a product. XCEL Energy and Centerpoint Energy, although many times less expensive, are not independant unbiased auditing companies. As with most things in life, you get what you pay for.

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