What causes Ice Dams?
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.
Warm air in the attic causes the underside of the snow to melt, which then runs down to the edge of the roof towards the gutters where the temperature is colder and refreezes to form an ice dam. Once an ice dam has formed, the melting snow will continue to enlarge the ice dam, backing up under the roofing and taking water with it. That water will find somewhere to go and the result is often interior water leaks - ruining insulation, drywall, ceilings, and damaging gutters.
Not every snowstorm will cause ice dams. Ideally once the snow starts melting from interior heat the exterior air will be warm enough that the melting snow will simply run down the gutters, as water should, instead of refreezing. In dryer climates, the snow might evaporate. Unfortunately snowstorms are not always ideal.
Attic air sealing, proper insulation and ventilation can prevent ice dams
Attic access door or hatch may not be properly sealed and insulated.
Air leaks around cabling, electrical wiring, light fixtures also need to be sealed.
Recessed lights can generate a great deal of heat in the attic. Old styles cannot be insulated due to fire hazards. They should be replaced with approved fixtures and insulated.
Heating ducts should be sealed and insulated not only to keep the attic cool, but to prevent heat loss from living spaces.
Vent pipes from a heating source need to be up to code in order to insulate and seal around them. Warm attics, heat loss, air quality, and fire hazards all come into play with improper vent pipes.
Proper attic ventilation prevents heat build up and moisture from collecting.
Preventing ice dams not only saves your roof and gutter system, it improves the air quality and health of your home. Water damage is costly due to repairs, but it is also costly due to health problems. Mold and mildew are often the aftermath of ice dams and water damage and sometimes goes undetected which can trigger asthma and other health problems.