What Are Ice Dams?
Ice dams are formed when heat from the inside of a home escapes into the attic and warms the roof decking during the winter. This heat, combined with heat from the sun, can melt snow on the roof. Melting snow on the upper roof and in the valleys then runs down toward the eaves as water. When it reaches the cold eaves and gutters it refreezes. The continual thaw and re-freeze process creates ice dams. The result is water backing up under the roof shingles or behind fascia boards where it can soak through the roof decking or wall sheathing, causing damage to attics, ceilings and walls.
Ice Dam Defense Background
There are three ways to defend against the damage ice dams cause: insulation, ventilation and water-proofing shingle underlayment. All three work together. Insulation keeps heat from escaping a home’s living space into the attic. Ventilation removes the heat and helps keep the roof deck evenly cool to help prevent snow from melting on the roof. Finally, waterproofing shingle underlayment, such as CertainTeed’s WinterGuard,™ is laid across the roof before roof shingles are applied.
Ventilation Component Details:
It is important to have proper ventilation in the attic so any heat lost from the interior of the home is drawn up and out of the attic. Adequate attic ventilation will help the roof deck stay cool. Another benefit of having an attic ventilated is that it allows for moisture that rises into the attic from things such as bathing, cooking and the laundry to escape. Unchecked moisture can promote mold, mildew, and wood rot.
Waterproofing Underlay Details
It is extremely important that waterproofing shingle underlay be installed before roof shingles are applied in the areas listed below. As mentioned earlier, it is completely resistant to water and, as such, is a critical last line of defense against leaks, preventing backed up water from getting into a home wherever it is applied.
Recommended areas that waterproofing underlay be applied:
- Under metal flashing and counter flashing at roof penetrations, sidewalls, etc.
- In areas where roof pitches change, in valleys and around chimneys.
- Along the eaves and at short cornice projections.