Icicles hanging from your roofline may look harmless, but might signal ice dams forming along the eaves. These ridges of ice develop when melting snow refreezes at the roof’s edge, trapping water behind it and increasing the risk of leaks and structural damage.
While quick fixes can help manage the problem in the moment, preventing ice dams requires understanding what causes them and how to stop heat from escaping into your home’s attic. In this guide, we cover fast ice dam removal methods, long-term solutions, and prevention strategies, with expert advice from This Old House Magazine and general contractor Tom Silva.
What Are Ice Dams?
Ice dams occur when snow melts on a warm roof and the water refreezes at the colder eaves. As Silva explains in the “How To Prevent Ice Dams” segment of This Old House, the root cause often starts inside the home. Heat rises into the attic, warming the roof deck and melting the bottom layer of snow. He notes that shingles are designed to shed water downhill, but when meltwater refreezes at the eaves and builds up, it can back up and work its way under the shingles.
This cycle of melting and refreezing allows ice to build up along the roof edge. As more water flows down and refreezes, the dam grows, trapping water behind it and increasing the risk of leaks and structural damage. Left unchecked, this buildup can force water under shingles and into your home, leading to leaks and interior damage.
How To Prevent Ice Dams
Preventing ice dams starts with keeping your roof at a consistent temperature so snow doesn’t melt unevenly and refreeze at the eaves. While some solutions address the problem from the outside, others focus on reducing heat loss from inside the home.
One option is to install heated roof cables, which can help control ice buildup along the roof edge. Attached with clips along the roof’s edge in a zigzag pattern, heated cables help prevent ice dams that lift shingles and cause leaks. This solution allows you to equalize your roof’s temperature by heating it from the outside rather than blowing cold air from the inside. Just be sure to install the cables before bad weather hits.
Heated cables can help manage ice buildup in problem areas, but they don’t address the underlying cause. Silva cautions that heated cables are only a temporary fix: “The only way to prevent it is with heat cable in the gutter and downspouts, but that’s really just a Band-Aid and doesn’t fix the problem.” The long-term solution is to improve ventilation and seal heat leaks that warm the roof from below.
Removing Existing Ice Dams
If you already have ice dams, there are several methods to remove them safely.
Apply Cold Air
For a quick fix when water is actively leaking, take a box fan into the attic and aim it at the underside of the roof where the leak is happening. The targeted cold air should help the water freeze.
This fix is by no means permanent, but it can buy you some time to make a more permanent fix. This method works by lowering the temperature of the roof deck in a specific area, rather than addressing the underlying heat loss.
As This Old House Magazine describes, Silva has used this approach during emergency calls to stop active leaks. By directing a box fan toward the underside of the roof near the problem area, he quickly cooled the roof deck, froze the water in place, and stopped the leak within minutes.
Use a Roof Rake
A long-handled aluminum roof rake can help you safely remove snow from your roof and deposit it onto the ground. Choose a rake with wheels, which will be much gentler on your shingles.
The Pantyhose Method
You can also diminish the damage after the dam has formed with… pantyhose! Fill the leg of a discarded pair of pantyhose with a calcium chloride ice melter. Lay the hose onto the roof so it crosses the ice dam and overhangs the gutter.
If necessary, use a long-handled garden rake or hoe to push it into position. 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.
Permanent Fixes for Ice Dams
While quick fixes can help manage immediate leaks, lasting solutions require addressing the conditions that allow ice dams to form in the first place.
Silva explains in the “How To Prevent Ice Dams” segment that the root cause often starts inside the home. Heat rises into the attic, warming the roof deck and melting the snow above it. That meltwater flows down the roof until it reaches the colder eaves, where it refreezes and begins to form a dam.
Getting rid of ice dams for good is simple, in principle. Keep the entire roof the same temperature as the eaves. You do that by increasing ventilation, adding insulation, and sealing off every possible air leak that might warm the underside of the roof.
By taking care of common trouble spots, listed here in order of priority, you should enjoy dam-free winters by winterizing your roof and using less energy to boot. These improvements work together to keep cold air moving through the attic and prevent warm air from reaching the roof deck:
- Ventilate eaves and ridges. A ridge vent paired with continuous soffit vents circulates cold air under the entire roof. Both ridge and soffit vents should have the same size openings and provide at least 1 square foot of opening for every 300 square feet of attic floor. Place baffles at the eaves to maintain a clear path for the airflow from the soffit vents.
- Cap the hatch. An unsealed attic hatch or whole-house fan is a massive opening for heat to escape. Cover them with weather-stripped caps made from foil-faced foam board held together with aluminum tape.
- Exhaust to the outside. Make sure that the ducts connected to the kitchen, bathroom, and dryer vents all lead outdoors through either the roof or walls, but never through the soffit.
- Add insulation. More insulation on the attic floor keeps the heat where it belongs. Check with your local building department to find out how much insulation your attic needs.
- Install sealed can lights. Old-style recessed lights give off great plumes of heat and can’t be insulated without creating a fire hazard. Replace them with sealed “IC” fixtures, which can be covered with insulation.
- Flash around chimneys. Bridge the gap between the chimney and house framing with L-shaped steel flashing held in place with unbroken beads of a fire-stop sealant. Using canned spray foam or insulation isn’t fire-safe.
- Seal and insulate ducts. Spread fiber-reinforced mastic on the joints of HVAC ducts and exhaust ducts. Cover them entirely with R-5 or R-6 foil-faced fiberglass.
- Caulk any other leaky spots. Seal around electrical cables and vent pipes with a fire-stop sealant. Also, look for any spots where the light shines up from below or the insulation is stained black by the dirt from passing air.
