Ice dams can form on pitched-roof overhangs in cold climates such as Minnesota. Heat loss through the roof and heat from the sun (even in freezing temperatures) can cause snow on a roof to melt. As water runs down the roof onto the overhang, it freezes and forms an ice dam just above the gutter. The ice dam traps water from melting snow and forces it back under the shingles and into the building’s interior.
Watch the edge of the roof overhang for evidence of ice dams and look at the eaves and soffit for evidence of deterioration and water damage. If the house has an attic, the underside of the roof deck at the exterior walls can be checked for signs of water intrusion. Ice dam removal is a pain, so try to prevent them from forming in the first place. The key to preventing ice dams is simply to keep your attic and roof cold. After a snowfall, a cold roof will have a thick blanket of snow. A warmer roof, however, will soon have clear spots where the snow has melted off, and may well have icicles hanging from the eaves.
To keep your roof cold, follow these steps:
Close up attic bypasses
The Minnesota Energy Code says "An attic bypass is any air passageway between a conditioned space and an unconditioned attic." Attic bypasses are the driving force behind ice dams, as well as frost, moisture, and mold in the attic. If you eliminate all attic bypasses, you'll probably eliminate all of these problems. That's why it's so important to address attic bypasses before doing anything else.
Sealing attic bypasses will also help to reduce energy bills and help with the comfort of your home. In reality, the biggest source of heat loss is through the attic, and the best return on investment is usually accomplished through air sealing and re-insulating the attic.
Measure your attic insulation level
Many home attics in Minnesota have some insulation; most can benefit by adding more attic insulation. Increasing attic insulation to an R-60 can provide a good barrier to heat loss (the code minimum for new buildings is R49). To determine the present R-value of your attic, have an energy assessment.
You can also measure the height of the insulation and multiply times the R-value per inch of the material that is in place (2.5 to 4.0 per inch, on average). Roughly 12 to 20 inches (depending on the material used) will provide an R-50 rating. Although it generally won’t hurt to add more, the return on the investment decreases as the R-value increases above R-50.
Add roof and soffit vents
Roof vents allow airflow through your attic or roof space, helping balance temperatures and preventing moisture build-up. In the hot summer months, they enable hot air to escape, reducing the strain on your air conditioning system, while in the colder months, they prevent ice dams and mitigate the risk of mold and mildew growth. This ventilation process ultimately protects your roof and your home’s interior.