This article is from American Reliable/GLOBAL Insurance Companies:
An ice dam is when ice builds up on the edge of a sloped roof and keeps melted snow (water) from being able to drain off of the roof. The water that gets trapped behind the dam can leak into the building, causing damage. The primary cause of ice dams is a difference in temperature along various parts of the roof.
These are basic tactics that can be used to prevent ice dams:
• Decrease heat transfer from the interior by insulating hatches leading to attics, insulating ductwork, and sealing areas around chimneys and flues.
• Block moisture accumulation from the exterior – make sure your roof covering and soffit areas are in good working order and are not damaged.
• Keep your roof gutters and downspouts clear of all debris. This will help to prevent accumulation of melting snow and ice.
• Trim back all trees with branches that overhang the roof. Snow from these branches could fall on your roof, increasing the potential for ice dams.
The preceding document is provided as an example for informational purposes. We (GLOBAL) make no charge of being experts in any field other than insurance. These documents are provided for informational purposes and we advise that you check with local, state, or federal authorities regarding codes or ordinances in your area.