Ice Dams - A winter headache you can avoid!
Ice dams are most common in cold climates. They occur when heavy snow buildup melts during the day and then refreezes when temperatures drop overnight. After several days of melting-freezing cycles, it is common for the melted water and ice to work up under the shingles until water enters the attic and eventually does damage to the ceilings, walls, and contents. The graphic below shows an ice dam on a roof. In cases where the ice dam goes unnoticed for an extended period of time, it can do significant damage to the building and its contents.
There is no way to guarantee an ice dam will not damage your home, but you can take the following steps to cut the chances of an ice dam forming in the first place:
Thoroughly clean all leaves, sticks and other debris from your home's gutters and down spouts. This allows melting roof snow to flow into gutters and through down spouts.
Make every effort to keep snow on your roof to a minimum. Long-handled devices on the market called "roof rakes" let you stand on the ground and pull the snow off the roof. Keeping heavy snow loads off of your roof reduces the chances for both ice dam formation and roof failure due to the weight.
All winter long, keep gutters and down spouts clear of snow and icicles.
Evaluate the insulation and ventilation in your attic. Consult the Building Code for minimum R values (R value is a numerical indicator of insulation effectiveness , the higher the number the more insulating value) for your location. Good airflow from under the eaves or soffit area along the underside of the roof and out through the roof vents is essential. The insulation prevents heat loss from the interior of the home. The venting allows the attic air to stay cold enough to prevent or minimize the freeze/thaw cycle on the roof. Consult a reputable roofing and/or insulation contractor about these improvements.
If replacing your roof, make sure that ice and water shield is used along the edges and at least 48 inches up from the edge of the roof. Code minimum is 24 inches, but the extra width is nominal in cost for the protection it provides.