Ice dams may form on your roof in the winter time and can be a major roofing problem. Melting snow, which is essentially water, cannot bypass the ridge of ice on your roof, so it backs up behind a dam of ice and can potentially leak into your attic. Moisture damage is expensive and hard to eradicate.
However, if you do have ice dams, they are not caused by a problem with your roof. Ice dams are caused by warm air circulating underneath the roof in your attic. So, the dams form due to poor weatherization. If you have ice dams, then contact an Energy Auditor for the best solution for your attic. A combination of insulation and airsealing can help prevent ice dams from forming.