Ice dams are a fact of life in snowy areas of the country. Insurance companies pay millions of dollars for claims involving ice dams that cause roof leaks every year, but it’s never enough to cover the time and aggravation of getting things fixed correctly.
The good news is, ice dams and the leaks they often cause can be reduced and even eliminated with proper insulation and venting.
Keep your attic and roof cold to minimize (or prevent) ice dams.
After a snowfall, a cold roof will have a thick blanket of snow. A warmer roof will soon have clear spots where the snow has melted off, and may well have icicles hanging from the eaves.
Fact: In the average home, about one-third of the heat loss is through the ceiling into the attic. Most of that heat loss comes from air leaks caused by unblocked walls, gaps in drywall, and cracks around light fixtures, plumbing pipes, chimneys, access hatches, and other ceiling penetrations.
Fix: Upgrade attic insulation, plug up air leaks to the attic and improve attic ventilation.
How to do this:
- Check the depth of your attic insulation. Building codes require about 12 to 14 in. of fiberglass or cellulose. Add more if you have less than 8 in. and have had ice dam problems in the past. Blown-in cellulose and fiberglass are usually better than hand-placed batts, because they fill more tightly around rafters, joists and other obstructions, leaving fewer gaps.
- Add roof and soffit vents. Attic ventilation draws in cold outdoor air and flushes out warmer attic air, cooling the attic and the roof in the process. The minimum ventilation area (size of the openings) should be about 1 sq. ft. of vent per 300 sq. ft. of ceiling area (attic floor area), when half the vent area is low on the roof and half is high.
Bonus: By stopping air leakage to mitigate ice dams, you’ll save energy and reduce both your heating and air conditioning bills.
If you’ve got a cold roof and are still getting ice dams, here are some secondary measures you can take.
The cheapest solution is to use a snow rake to pull the snow off your roof after a heavy snowfall. It’s an effective solution, but not advised for multi-story homes: never use a snow rake when standing on a ladder! Also, take care not to break the roof shingles, which are brittle in cold weather.
Install heat cables when all else fails. Heat cables are high-resistance wires that you mount on the roof edge in a zigzag pattern and plug into an outdoor GFCI receptacle. They’re ideal in spots where ice dams regularly occur and can’t be stopped any other way. One problem: You have to route the meltwater away. Otherwise, it’ll refreeze in the gutters and along the roof edge. Run the heat cable inside a downspout so the downspout doesn’t clog with ice.
Run special adhesive ice-and-water barrier from 3 to 6 ft. up the roof from the edge the next time you reroof. This barrier is a type of self-sealing underlayment that adheres to the roof decking and waterproofs it. You shingle over the top of it. It’s required by the building code in most regions now. Adding it is expensive if you have to tear up an otherwise sound roof, but it’s cheap insurance if you have to reroof anyway.
What to do if you already have an ice dam.
Ice dams themselves aren’t necessarily a problem. It’s the leaks they cause that do most of the damage. If you can’t detect signs of ice dam leakage, either in the soffits on the outside or in the attic or ceilings, you may not have to do anything.
If you have leakage from an ice dam and can’t rake the snow off the roof, the best way to get rid of the ice dam is to hire a roofing company to steam it off. A steamer is like a pressure washer, except that the water is hot. It melts the ice away without damaging the roofing. Chipping the ice off with a hatchet or an ice pick can break or puncture the shingles.