Ice dams are normally brought about by large snowfall and poor air flow in the attic. This causes warmer regions in your attic then the snow commences to melt, even when the exterior temperature is properly underneath freezing. When the accrued snow on your roof begins melting it runs down your roof beneath the snow until finally it reaches a "colder" portion like the soffit's, valleys or in gutters then it starts to freeze yet again, this procedure of thawing and refreezing is what leads to an ice dam. My websites: (ice dam remover)