The accumulation of ice at the eaves and valleys of roofs (ice damming) may prevent melted ice and snow from draining off the roof, and cause the water to back up under the roofing, and leak into the building interior. To prevent ice damming, the attic must be well ventilated. This will allow the roof to maintain a more uniform temperature by quickly removing any warm air that reaches the attic space. In addition, the ceiling must have an adequately sealed air and vapor barrier, and be well insulated to prevent excessive heat loss to the attic. Important techniques to employ include:
- Ensuring correct installation of insulation at eaves
- Ensuring adequate airflow through attic eaves.
- Ensuring adequate ceiling insulation to keep warm air from rising to attic and through roof.
- Carefully sealing all ceiling penetrations (light fixtures etc.); to keep warm, moist air out of the attic.