Home Improvement Exterior Remodel Roof

How to Prevent Ice Dams on Roofs

Roof ice dam
Sawayasu Tsuji / Getty Images
In This Article

Homeowners in snowy, cold-winter climates are likely familiar with ice dams or masses of ice that gather along the lower edge of a roofline where it overhangs the edge of the home. Some homes may be burdened with huge blocks of ice thickly covering the roof eaves, while others have only a bright snow cap over the shingles with no signs of ice. Left alone, ice dams can cause considerable home damage.

Problems With Ice Dams

  • Compromising the roof: Severe ice dams can weigh hundreds of pounds, compromising the structure of the roof eaves potentially causing a roof cave-in. It is a safety hazard to home residents and requires expensive roof repairs.
  • Heat loss in the house: Melting ice water that leaks into the house can reduce the home's R-value or capacity to retain heat and keep the home insulated, requiring homeowners to expend more energy and money to heat a home.
  • Short-term damage: Ice dams can cause meltwater to back up under the shingles, where it can cause water damage, flowing down and ruining ceiling and wall surfaces. 
  • Long-term damage: If ignored, ice dams can cause significant damage requiring roof replacement or can cause structural rot, mold, and mildew damage in your roof, gutters, paint, insulation, interior drywall, attic space, and other surfaces.

What Causes Ice Dams?

Diagram of an ice dam
This diagram by Owens Corning shows how an ice dam forms and how leakage may occur in your home. Owens-Corning

Ice dams are caused by snow melting on an upper, warmer part of a roof, and then that water flows down to the colder eave overhang, where it refreezes. As the ice accumulates, it forms a blockage that prevents additional snowmelt from flowing off the roof. The ice begins to back up under the roof shingles, where it melts again, soaking the roof sheathing and leaking into the attic.

Ice dams are formed only when the space inside an attic along the underside of the roof deck is above the freezing point. As the warm air beneath the roof heats the shingles and melts the snow on the roof, the water flows down the roofline until it reaches the overhanging eave structure and refreezes.

Ice dams usually start or worsen after heavy snow because of snow's insulating properties. The snow layer traps warm air beneath the snow, which causes it to melt. 

How to Prevent Ice Dams

Preventing ice dams is a matter of simple thermal physics. If the air in the attic or against the bottom of the roof deck remains cold, it can never melt the snow on top of the roof, eliminating the water necessary for ice dams. Prevent ice dams by performing a combination of methods.

  • Ventilation under the roof deck: Circulate the colder outside air through the attic to prevent it from warming above the freezing point so it doesn't melt snow on the roof.
  • Insulation in the ceiling: Prevent warm air from rising into the attic space by lining insulation in the ceiling space below the attic.
  • Block heat sources: Heating ductwork in the attic, light fixtures near the roof, or heated living space in the attic area can all contribute to heating the roof.
  • Use electric heat cable: Heat cable can prevent melting water from refreezing, allowing it to drip or flow off the roof.

Preventing Ice Dams With Ventilation

Houses with good attic and roof ventilation generally do not experience ice dams. By circulating cool outside air in the attic space, soffit, or rafter spaces just below the roof deck, the roof surface remains below freezing and cannot melt the snow on the roof. 

This logic may seem contrary to what's good for a home, but a warm roof is worse since it can lead to ice dams. Look at roof venting systems as a way to keep your roof cool in winter.

  • Soffit and ridge vent system: This system creates a continuous airflow from the soffit (underneath the roof eaves) to the roof's peak and requires insulation baffles installed at the lower side of the roof, above the exterior walls. Baffles hold back insulation 1 to 2 inches, allowing air to flow past the insulation. This works with a ridge vent, allowing air to flow through the baffles with a path to outdoor air. Avoid using thick insulation that blocks airflow.
  • Soffit or gable vents with conventional roof venting: Use soffit or gable vents for intake air and several conventional roof vents for exhaust air. Ventilation systems should provide 1 square foot of net free ventilation per 150 square feet of attic floor space. Net free ventilation is the total area of openings in a vent minus all screening or other obstructions. 

Preventing Ice Dams by Insulating

Leaves on a roof
R Sherwood Veith/Getty Images

Another method to prevent heat from rising to the roof deck is to insulate the ceiling in living spaces below the attic or against the inside surface of the roof. If you have an open attic, this means insulating the attic's floor. If you have a finished second story with a finished ceiling directly against the roof, insulate the rafter spaces (and use ventilation baffles).

Sealing air channels from the living space below the attic is as important as the insulation. Seal gaps around plumbing pipes and chimneys since they can be a significant source of heat flow into the attic from the spaces below.

A comprehensive insulation plan prevents ice dams and reduces energy costs. However, insulation alone is rarely enough to prevent all ice dams; combine it with improved ventilation.

Preventing Ice Dams by Eliminating Attic Heat Sources

You may also have heat sources in your attic that you're unaware of. Older recessed lights (can lights) may extend up into the floor of the attic and can radiate heat into the attic—enough to heat the air above the freezing point (especially if ventilation is poor). Replace old fixtures with fully insulated modern recessed lights to reduce heat radiating into your attic.

Other possible heat sources include uninsulated HVAC ductwork, vents from clothes dryers, and improperly vented bathroom or kitchen exhaust fans. These heat sources should be wrapped in fiberglass insulation to reduce heat transfer into the attic space.

Preventing Ice Dams With Electric Heat Cable

If the first methods aren't practical and you have an ice dam problem, install an electric heat cable along the edge of the roofline and gutters. Heat cable may appear unattractive on a roof but prevents ice dams when appropriately installed. 

When looped in a zig-zag pattern along the roof's edge, the heating cable prevents melting water from cooling enough to freeze when it reaches the eaves. Instead of freezing, the meltwater flows to the ground.

Warning

Beware when using heat cables since water mixed with electricity has its risks. Closely follow the manufacturer's directions. Check and maintain the heating cable regularly to ensure that it remains safe. 

How to Get Rid of Ice Dams Fast

Steam ice dam removal
Absolutely Clean Window Washing

Preventive efforts are best conducted during the spring, summer, or fall, but several options exist for mitigating them during the cold months.

  • Keep gutters clean. Remove fall leaves and clean out gutters before the snow comes. Also, check downspouts are not clogged and are functioning correctly.
  • Use a roof rake after heavy snowfalls: Use a long-handled roof rake and apply light pressure to prevent shingle damage. Remove the snow from at least the lower 4 feet of the roof edge. A roof rake is the only safe way to remove snow from a roof. Never get onto a roof to remove snow in the winter.
  • Use calcium chloride or an ice-melt product: Apply calcium chloride or a similar ice-melt product to melt the ice.
  • Chip off the ice: Instead of climbing onto the roof, use an extension ladder at the eaves level to chisel away some of the ice by hand. It is not necessary to remove the entire ice dam but to open up a channel for meltwater to flow off the roof. This method may require a lot of repetition since it will likely refreeze and dam up again.
  • Hire a professional: Since most roofers halt their regular roofing work in winter, consider hiring a roofing service to remove an ice dam problem. These insured professionals have special equipment to make fast work of ice dam removal.

Tip

Never hire a contractor who offers to remove your ice dam with a high-pressure power washer with a steam box. This method will likely damage shingles. 

FAQ
  • Does homeowner's insurance cover roof damage from ice dams?

    Many insurance companies will pay for some or all of the damage caused by ice dams. However, you must read the fine print of your policy to determine if ice dam damage is covered, what is included in the coverage, and if there are any exclusions.

  • What is the most likely cause of ice damming on a roof?

    Ice dams are most commonly caused by heavy snow buildup that melts during the day and refreezes when temperatures drop overnight.

  • Should you remove ice dams from the roof?

    Remove ice dams when possible to prevent damage to your roof and home structure. Put preventive measures in place so they don't become a problem.