The physics of ice dams: Why roof heat is the culprit#
When warm indoor air leaks into an unsealed attic, it warms the upper roof deck above 0°C (32°F). Snow melts, runs down to the cold eave overhang, and freezes into a solid ice dam. Trapped water then backs up under shingles.
Three-step ice dam remediation strategy#
- 1. Air sealing ceiling bypasses: Seal pot lights, plumbing stacks, attic hatches, and chimney chases with expanding foam.
- 2. Proper rafter ventilation baffles: Install continuous plastic baffles at eaves to prevent insulation from blocking soffit airflow.
- 3. R-50 to R-60 insulation: Blow in 16–18 inches of cellulose or fiberglass insulation to maintain a cold roof deck.