Ice dams occur when snow is present on the roof and the outside temperature is below freezing. Homes with poor insulation allow heat to escape from the living quarters into the attic. If the roof system is not properly ventilated, the heat will build up in the attic and warm the roof deck, melting the snow above. When the melted snow reaches cooler roof areas, usually the gutters or areas near the overhang (eaves) it will refreeze. This freeze-thaw process can damage shingled roofs since the ice can travel “upslope” and get underneath the shingles.
Prevention and Protection
Installing new shingles will not prevent ice dams. Prevention only occurs when the entire roofing system is addressed, including attic insulation and roof ventilation. Ideally, the temperature in the attic space should be close to the same temperature as the outside air.
- Attic Insulation – adding insulation to your attic will minimize the heat that escapes from the living space into the attic. Additionally, electric outlets, plumbing vents, furnace stacks, and bathroom vents can allow heat to escape into the attic.
- Roof Ventilation – inevitably, heat will get into your attic during winter months. Proper roof ventilation allows that heat to escape and prevents your roof deck from warming. The freeze-thaw process that results in ice damming is unlikely to occur on a roof that is properly ventilated.
- Underlayments protect the roof deck from ice dams by creating a water-tight barrier between the shingles and the roof deck, but do not prevent ice damming from occurring.