What are ice dams?
If you’ve ever had pretty icicles hanging from the edge of your roof, you’ve had potential for ice damming. Ice dams start with ridges of ice that form when snow on the upper part of your roof melts. Water runs down the roof slope—often under the snow at the eave’s edge—and refreezes at the edge of the roof. This prevents additional melt from getting to the gutters, so it may leak into your attic, walls, and ceilings, ruining insulation, shingles, fascia, or soffits, and causing mold and mildew in the walls and attic. Unfortunately, until the water runs through your ceiling, you may not even be aware there is a problem; by the time you notice, you may have major damage to your home.
How to tell if ice dams are forming
Any time there is a heavy load of snow on your roof and you see icicles forming on the edge of the roof, look for pooling water near the eaves. Then check for these potential problems that can be caused by that snow melt:
Stains running down exterior walls just below the eaves
Rot on exterior walls or in the attic
Blistering paint on soffits on exterior walls
Rusty nail heads on the exterior or in the attic
Matted attic insulation
Blistered or peeling paint on interior walls
Preventing ice dam problems
Keep your roof cold through adequate insulation or ventilation. Close up areas that could allow warm air from your home to get into your attic by: adding insulation and filling gaps in drywall, cracks around light fixtures, plumbing pipes and other ductwork, chimneys, access hatches, bathroom fans, and any other ceiling penetrations. To do this in the attic, rake back insulation and plug leaks using foam or caulk.
Adequate ventilation may also help prevent ice damming, according to some experts, while others say that if minimal heat escapes into the attic, ventilation isn’t critical. If your roof is carrying a heavy load of snow, the ventilation holes may be plugged.
Other solutions promoted to prevent ice damming
There are a number of options promoted, all of which have caveats for use. But remember these do not solve the real problem—excessive heat loss from your home:
Snow rake. Raking snow off your roof takes a toll on your shingles because they are brittle in the winter, and because getting up on the roof in winter is dangerous, rakes are never advised for homes higher than one story.
Electric heating cables. These are available at home stores, but may or may not be allowed by your building code. They are supposed to keep the roof warm, so that snow doesn’t pile up. The downsides: They can make shingles brittle, water may refreeze in the gutter unless the melted water is routed away, and they may be a fire hazard.
Adhesive ice and water barrier. Adding this self-sealing, waterproof underlayment can only be done when re-roofing (some building codes require it). It is usually attached for 3 to 6 feet up the roof from the gutter and shingles go over top. The plus: Water shouldn’t leak through the barrier. The downside: Ice dams may occur higher on the roof’s surface and water may leak into your roof at the higher point.
Sheet metal ice belts. These are 2-foot wide strips of metal put on top of the shingles at the edge of the roof. The downside: They are unattractive and won’t stop problems from occurring higher on the roof.
Hire a roofing company to steam the snow off. This is a big pressure washer; the process is expensive and would have to be repeated every time a load of snow lands on the roof.
A word of caution
It’s dangerous to be on the roof when there’s ice and snow cover. There is the risk of personal injury and potential damage to the roof. Also tightening up your home could cause ventilation problems, especially if natural gas or propane comes into your home. Backdraft, exhaust, or combustion problems can lead to carbon monoxide poisoning in homes with gas lines.