While dangling icicles and a snow-piled roof make for a cozy winter picture, ice dams can cause major damage to the home.
In this guide, we’ll cover everything homeowners need to know about ice dams, including:
What causes ice dams?
Ice dams are caused by inconsistent roof surface temperatures. When warm air from the attic rises and melts the snow on the roof, meltwater flows down to the eaves of the roof and refreezes. Shortly after the water freezes and turns to ice, meltwater from higher and warmer points on the roof quickly backs up behind the dam, preventing proper water drainage.
As described by the University of Minnesota, “Heat loss from a house, snow cover, and outside temperatures interact to form ice dams. For ice dams to form there must be snow on the roof. Higher portions of the roof's outside surface must be above 32 degrees F (freezing) while lower surfaces are below 32 degrees F. These are average temperatures over sustained periods of time. For a portion of the roof to be below freezing, outside temperatures must also be below freezing.”
Additionally, roofing materials with poor energy efficiency can create warm spots on the roof. For example, asphalt shingles absorb heat from the sun like a sponge, and in the summer they continue to radiate heat down into the home long after the sun sets. In winter, heat-absorbing asphalt shingles create warm spots on the roof.
Why are ice dams bad for the roof?
The pooled water trapped behind the ice dam can work its way into porous roofing materials like asphalt shingles, wood shake or clay tiles. When the water refreezes, it expands and puts substantial pressure on porous roofing materials, causing them to crack or split.
While ice dams can cause considerable damage to the roof itself, the pooled water can also penetrate the underlying roof deck resulting in secondary damage to walls, ceilings, insulation, siding and gutters.
For example, if water penetrates the attic, stains to exterior walls and damage to insulation ceiling finishes are major risks. This also makes for the perfect environment for mold and mildew to flourish.
How to Prevent Ice Dams
Since ice dams are caused by inconsistent roof surface temperatures, it’s critical to keep the temperature of the roof consistent from the highest ridge to the lowest eave.
A well-ventilated roof will draw the freezing outside air into the space beneath the roof and prevent the air in the attic from warming above the freezing point.
The issue with traditional roofing materials like asphalt shingles, wood shake, and clay tiles is that maintaining a consistent temperature is difficult because they lay flat and are installed directly on the roof deck. There is no space for air, insulation or anything else in between.
Since a well-ventilated roof requires airspace between the roof deck and the roof surface, look for a roofing material that can be installed in one of two ways:
- On battens.
- Directly to the roof deck and has built-in airspace of at least ¾”.
What you don’t want is a roofing material that is attached to the deck without any underlying airspace. Asphalt shingles, for example, are nailed directly to the roof deck and don’t provide any space for airflow.
Metal roofing, on the other hand, can be installed on either battens or direct-to-deck with the critical ¾” airspace required for proper ventilation.
The airspace makes your metal roof an excellent investment for increasing energy efficiency year round, since allowing heat to radiate up and away from the home in warm weather also reduces the cooling load of the home.
A metal roof is also non-porous, impervious to snow or water, and resistant to cracking, warping and buckling.
While the roofing material plays a major role in preventing ice dams, there are other steps homeowners can take to reduce the chances of ice dams forming, as recommended by the National Weather Service:
- Thoroughly clean all leaves, sticks, and storm debris from your home's gutters and downspouts. This permits melting roof snow to flow undeterred into gutters and through downspouts.
- Make every effort to keep the snow amount on your roof to a minimum. Long-handled devices called "roof rakes" let you stand on the ground and pull the snow off the roof. Keeping heavy snow loads off your roof reduces the chances of both ice dam formation and roof failure due to the snow weight.
- Throughout the winter season, keep gutters and downspouts clear of snow and icicles.
- Evaluate the insulation and ventilation in your attic. Most experts agree the R-value of attic insulation should be at least R-30 (R-38 is preferable in northern climates).
- Good continuous airflow from under the eaves or soffit area along the underside of the roof and out through the roof vents is essential. This is why metal roofing systems are one of the best solutions for dealing with ice dams. The ridge venting allows the attic air to stay cold enough to prevent or minimize the freeze/thaw cycle on the roof.
Prevent Ice Dams with DECRA Metal Roofing
Durable and long-lasting DECRA Metal Roofing products are engineered to withstand ice dams, snow, freezing temperatures, blizzards, hurricanes, tornados, hail and nearly anything Mother Nature has to offer.
See and feel the DECRA difference by ordering a complimentary sample today.