Damage control: Experts weigh in on best ways to manage ice on rooftops

This story was originally published Feb. 27, 2010The ice dam cometh. Like it or not, this has been the ideal winter for ice dams.
Hiring a contractor to remove the snow from your roof will save you time and some aches and pains. Associated Press

This story was originally published Feb. 27, 2010The ice dam cometh.

Like it or not, this has been the ideal winter for ice dams. Ample snowfall and multiple snow-thaw cycles have contributed to those ridges of ice that form around a home's eaves, potentially causing homeowners thousands of dollars in repairs.

"With the icy conditions, people who have never had them before are having problems this year," says Wyatt Fernow with Western Products in Fargo.

So how do you make the ice dam goeth?

The Forum gathered ideas from roofing contractor Fernow, an Extension agent and a facilities engineer. They say the solution ranges from some quick fixes - such as using special rakes to keep rooftops clear of snow - to pricier, long-term approaches.

Birth of an ice dam

All those icicles hanging along the eaves can look pretty, but they may indicate trouble up above, says Ken Hellevang, an Extension agricultural engineer at North Dakota State University.

Ice dams form when the heat from the upper portion of the roof is warm enough to melt snow, yet the eaves are cold enough to freeze runoff into icicles. When the melting water reaches the cold eaves down below, it freezes. As more water flows down and hits that point, the ice builds up to form a ridge. As the cycle repeats, water will pool up behind the dam. With nowhere to go, the pooled water will either seep under shingles and leak into the attic or walls or will overflow and form icicles.

In the process, the ice dam and meltwater can cause:

  • Gutters and shingles to dislodge.
  • Soaked, ineffective insulation in attic walls and exterior walls.
  • Stained, blistered, peeling siding on outside.
  • Stained, cracked and spalled plaster and stained, blistered paint on interior walls.
  • Unhealthy mold and mildew formation.

"It can actually rot boards," says Vern Borgen, a facilities engineer with the USDA's Agricultural Research Center in Fargo. "It can cause severe damage to a house. Anywhere from $10,000 to $20,000 in damage would be fairly easy to do."

Long-term solutions

One of the main culprits of ice dams is heat loss through the attic, which causes snow to melt on the top of the roof, Borgen says. This heat loss is typically caused by insufficient insulation or ventilation in your home's attic space.

Other heat-loss magnets include recessed lights, skylights, attic hatches, chimneys and exhaust systems that terminate just above the roof, according to the University of Minnesota Extension Service.

The following steps aren't particularly quick or easy, but can provide long-term fixes:

  • The next time you have your home reshingled, make sure roofers use several layers of waterproof, self-sealing rubber membrane underneath the shingles. Most state building codes actually require this membrane, which won’t necessarily prevent ice dams, but will help prevent water from leaking back into your house, Fernow says.
  • Provide good attic ventilation to replace warm air in the attic with cold outside air. Increasing ventilation – at a rate of 1 square foot of vent for every 150 feet of attic – can help to remedy this problem. Position it so half of the vent area is near the roof peak and half is at the eaves. Also install air chutes to assure the eave vents are not blocked by insulation.
  • If your home’s roof overhangs the outside walls, consider adding vents into the overhangs (soffits). To complete the ventilation system, add a ridge vent, a specialized vent that mounts along the length of the peak of the roof. Cold air will enter the soffit vents and rise inside the roof before exiting out of the ridge vent. This will not only keep the roof cool, but remove moisture.
  • Hire a contractor to build a “cold deck” over your roof. This involves installing two-by-fours, peak to edge, along the length of the roof. Then install roof boards on the two-by-fours. Install a vent at the peak and another at the eave to allow air to circulate under the new roof. Add shingles.

    This “cold deck” creates a natural insulation barrier that keeps the entire roof cool, Borgen says. Although it’s more involved and costly, it is a guaranteed solution for ice dams – and will boost your house’s energy efficiency considerably.

  • Provide adequate attic insulation to reduce the transmission of heat into the attic from living spaces below. (In this climate, aim for insulation with an R-value of 40.)

    Installing additional insulation on the attic floor can be as simple as laying additional batts across the existing one, or having a professional blow more foam insulation into that area. If doing your own installation, Borgen advises leaving at least a 2-inch air space between the underside of the roof and the insulation to allow air to circulate.

    Not sure about your insulation needs? Weatherization contractors, often listed under “Energy Management and Conservation Consultants” or “Insulation Contractors” in the phone book, are professionals who can deal with heat-transfer problems.

Quick fixes

But if you don't have the time or budget to build a cold roof or install a new ventilation system, you can prevent or temporarily fix ice dams with one of the following approaches:

  • While standing safely on the ground, pull off snow with a long-handled aluminum “roof rake,” available at hardware and home stores. A rake with wheels won’t harm the roofing. On a roof with a greater pitch, removing three or four feet of snow above the roof line should slow down the ice accumulation.
  • Hire a roofing contractor or gutter-cleaning company to carefully remove most of the snow from the roof above the ice dam. The contractor should avoid touching the roof with the removal equipment or even walking on the roof if possible. Cold roofs are more prone to damage because they are more brittle than they are in the summer.
  • If water is actively leaking into the house, take a box fan into the attic and aim it at the underside of the roof at the site of the leak. This targeted dose of cold air will freeze the water in its tracks, according to www.thisoldhouse.com.
  • In an emergency situation in which water is flowing into the house, make channels through the ice dam to allow the water behind the dam to drain off the roof, according to the University of Minnesota Extension Service. Hosing with tap water on a warm day will also do the job. Work upward from the lower edge of the dam. This will alleviate the problem, but only temporarily.
  • If dealing with a smaller dam, fill one leg from a discarded pair of pantyhose with calcium chloride snowmelt and lay it on the roof so it crosses the ice dam and overhangs the gutter. Use a long-handled rake or hoe to push it into position. (Do NOT use rock salt, which will stain the roof and siding.) The calcium chloride will eventually melt through the snow and ice and create a channel for water to flow down into the gutters or off the roof. Keep in mind, though, that the salt runoff may damage perennials and bushes close to the house, Hellevang says.
  • Install heat tape, or heat wire, in a looping, zig-zag pattern along the roof’s surface above the eaves, Hellevang says. The tape, which heats up when plugged into an outlet, creates channels in the ice to allow runoff, so water doesn’t pool on the roof. Although a bit pricey – $5 to $10 a linear foot – heat tape is less costly than more involved options.

Other sources: The New York Times, University of Minnesota Extension Center, www.thisoldhouse.com, Popular Mechanics, www.radioiowa.com, www.naturalhandyman.com, www.homeimprovementweb.com

Ice dam? What not to do:

  • Do not attempt to “chip away” the ice of an ice dam. It will likely lead to shingle damage.
  • Do not climb up on the roof yourself to remove ice or snow. By doing so, you will risk injury and risk damage to the roof. (Overhead power lines can also pose a threat.) Leave this work to professionals. If you must climb higher to get to the ice dam, work from a steadily anchored ladder.
  • Do not install mechanical equipment or water heaters in attics, especially in cold climates.

Readers can reach Forum reporter Tammy Swift at (701) 241-5525