If you live in a cold climate, chances are good that at some point your home may be affected by an ice dam. Ice dams can do quite a bit of damage, but if you’re aware of the situation, you can take some proactive steps to minimize or even prevent ice dams from forming.
Why ice dams occur
During the winter, snow builds up on the roof. If the winter temperatures are cold enough, the sun’s heat is insufficient to melt off much of the snow layer, so it remains in place, and even continues to grow.
In the meantime, you’re using the furnace or the fireplace to keep the house warm, and some of that heat is lost into the attic. With the snow on the roof acting as an insulator, the heat from the attic begins to work on the underside of the snow layer. Soon, a thin film of melted snow — liquid water — appears on the underside of the snow layer, between the top of the roofing and the underside of the snow. This water runs down the top of the roof, beneath the snow, until it reaches the eaves.
Once at the eaves, the water is past the end of the attic. Now there is no more heat being lost from the house to keep the water warm enough to remain a liquid. The water freezes, forming a dam. The cycle repeats itself, the dam grows, and the water backs up farther and farther. Once it backs up to the heated part of the attic again, it no longer freezes. Remaining as liquid water instead of ice, it works under the shingles and gets into the house.
The first sign of potential trouble is a layer of ice forming along the eaves of the house, right at the very edge of the roof. You may also see that ice has been accumulating inside the gutters and has finally grown high enough to be visible from the ground. At this point, you can carefully try to remove the snow layer from the eaves of the roof. The idea is to remove the insulating ability of the snow, so that when temperatures come up a little, the ice will melt. But DO NOT give in to the temptation to use a pick, sledgehammers, ax, blow torch, or other drastic measures!
Icicles are the next warning sign. They’re actually part of the ice dam, occurring as some of the dam melts, flows over the edge of the roof, and refreezes. As with the ice dam, as the cycle repeats itself, the icicles simply keep getting larger. Icicles warn you that the dam is getting worse. If the ice is sufficient to be dripping over the edge of the roof, it’s also moving farther up the roof. You might still be able to have a small amount of impact on the problem if you remove the snow at the eaves, but again, how much good it does seems to be totally weather-dependent. …CONTINUED
The third warning sign can take a couple of different forms, but they all relate back to water having gotten into places where you really don’t want it to be. One of the ones that people seem to notice first is a discoloration appearing inside the house, in the corner where the ceiling meets the exterior wall. This is caused when water backs far enough up the roof to get into the attic. It drips down and wets the insulation, then pools in the corner along the exterior walls. If enough gets in there, it will eventually wet the drywall to the point where water stains appear. Left unchecked, it will eventually cause the drywall joint tape to peel, and the drywall itself to deteriorate.
In some instances, the water will run down inside the wall instead. You may begin to see water stains appearing on the drywall at the bottom of the wall, or above or alongside windows and exterior doors where the dripping water encounters the horizontal structural headers that span those openings. In some extreme cases, you may even see puddles of water coming out onto the floor at the bottom of an exterior wall.
Another unwelcome sign is the appearance of ice behind or between siding boards, or coming out of soffit vents, or showing up in other exterior areas where ice has no reason to be. That’s an indicator that the water has gotten into the walls or into the soffits, and being outside the layer of wall insulation, it is freezing there. As temperatures warm, that ice will melt and potentially damage the insulation.
Preventing ice dams
To prevent the ice dam from forming, your best bet is to keep the roof cold. That might sound counterintuitive, but the theory is that if you can keep heat from reaching the underside of the roof, you’ll keep the bottom of the snow from melting. That keeps the water off the roof, which is what forms the dam in the first place.
There are two things to keep in mind when considering how to keep your roof cool. First, increase your insulation levels. By improving the amount of insulation you have in the attic, you decrease the amount of heat being lost from the house into the attic. The same goes for any ducts you have in the attic, which need to be very well insulated against heat loss. This is a win-win situation for you, because improving insulation levels not only helps with ice damming, it also saves on your utility bills, it improves your home’s comfort levels, and it’s good for the environment.
The other thing you want to do it be sure that your attic has good ventilation. You have to assume that no matter how good your insulation is, some lost heat is still going to reach the attic. When it does, you want to get rid if it in a controlled manner — in other words, not through the underside of the roof sheathing. The best way to do that is through good passive ventilation, which is an adequate number of low vents in the eaves or soffits, and high vents in the gable ends or along the ridge.
Remodeling and repair questions? E-mail Paul at firstname.lastname@example.org.
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