Ice dams can be caused by poor ventilation or attic design. Proper ventilation comes from both the air intake and exhaust working together. The roof vents allow air to escape the attic. However, to make this happen, fresh air must be permitted to enter from the area below the soffit. Airflow can be restricted if the soffits become blocked completely or partially. Ice damming happens when the snow melts from a roof during sub-zero temperatures.