The potentially damaging effects of ice dams are all too evident when watching
the recent collapse of the roof of the Metrodome in Minneapolis.
“While the chance of your roof collapsing from an ice dam is very small, ice
dams still can cause damage,” says Carl Pedersen, North Dakota State University
Extension Service energy educator.
This is the time of year when ice dams will begin to develop on roofs and
potentially cause damage. Homeowners have a few steps they can take to prevent
“The key is to ensure your roof is constructed properly with sufficient attic
insulation and ventilation to prevent the formation of ice dams,” Pedersen says.
An ice dam forms when snow melts and runs downs the surface of the roof. As the
melted snow hits cooler parts of the roof near the eaves, it refreezes. This
process continues and eventually creates a dam of ice on the roof.
As more snow melts, the dam stops the water, which freezes, making the dam
bigger, or backs up the melt water, allowing it to leak under the shingles into
the attic spaces or eaves. This can lead to water stains in the ceiling,
structural damage and mold growth inside the home.
Ice dams are clearly visible once they form, but to find out what causes them, a
homeowner needs to look inside the attic.
Heat from inside the attic is the major cause of snowmelt on the roof forming
ice dams. The greater the amount of heat in an attic, the greater the potential
for snowmelt and ice dams.
The attic is warmed with heat leaking from a home’s living space.
Anyplace where plumbing, heating or electrical components protrude into the
attic and the openings are not sealed properly can allow heat leaks to occur.
Recessed or “can” lights and attic access doors or ladders can be other areas
where heat leaks into the attic.
Even if all the leaks into an attic from inside the home are sealed, heat from
the home can be lost to the attic if the attic does not have proper insulation.
“The ability of insulation to stop heat loss depends on the type and thickness,
but attics in northern climates need roughly 18 inches of insulation to be
properly insulated,” Pedersen says.
Another cause of heat loss is improper ventilation of the attic space. Keeping
all the heat out of the attic space is impossible, so allowing that heat to
leave the attic through vents is important.
Depending on the construction of the home, this can be done through soffit
vents, vents on the gable ends of the home or a ridge vent. Make sure the
attic’s insulation does not block the air flow from the soffits or eaves. Use
baffles to create a channel to hold insulation back from the soffit vents to
allow air flow.
Removing snow from the lower portion of the roof so melting snow can run off is
another way to prevent ice dams from forming.
“However, removing snow from the roof can be dangerous, so avoid getting on the
roof by using a roof rake,” Pedersen advises. “You also need to take care to
avoid overhead power lines.”
For more information about this or other energy issues, contact Pedersen at
(701) 231-5833 or firstname.lastname@example.org, or visit NDSU’s energy website at