How to Prevent Ice Dams on Your Roof

Ice dams are not a roof problem; they are a heat-loss problem. When warm air escapes from your living space into the attic, it warms the underside of the roof deck, melting the snow sitting on top. As that meltwater runs down toward the cold eaves, it refreezes, forming a jagged wall of ice that eventually forces water backward under your shingles and into your walls. Stopping them requires a disciplined approach to building science: keep the heat inside the house and keep the roof deck as cold as the outside air. Done well, this process eliminates the temperature differential that causes melting, keeping your roofline clear and your interior walls dry throughout the winter.

1. Stop the Heat Escape. Identify air leaks where wires, plumbing pipes, or chimneys penetrate the attic floor. Seal these gaps using high-temperature spray foam or fire-rated caulk to stop warm, moist air from escaping your home.
2. Measure Your Thermal Gap. Measure the depth of your attic insulation. If you can see the ceiling joists, you are severely under-insulated and need to add more to reach a consistent R-value of at least R-49.
3. Open the Airflow Path. Install plastic soffit baffles between the rafters at the eaves. These channels ensure that the attic ventilation path remains open even after you add additional insulation.
4. Build Your Thermal Barrier. Blow in cellulose or roll out batts to cover the attic floor, ensuring an even layer across the entire surface. Pay extra attention to the areas above the exterior walls, where the roof meets the ceiling.
5. Confirm the Vent Path. Go outside and check that your soffit vents are not covered by paint or debris. Proper airflow is necessary to carry away any small amounts of heat that do reach the attic.
6. Complete the Ventilation Circuit. If your attic has poor circulation, install a ridge vent at the peak of the roof to allow the heat trapped at the highest point of the attic to escape naturally.