Ice Damming Prevention

From there the melted snow water works its way down to the roof eaves and roof valleys where the ice dams form.

Ice dams typically occur at roof eaves and roof valleys. With roof eaves snow melt higher up on the roof melts from the underside and drips down towards the roof edge (or eaves). As the melted snow water reaches the roof eaves it freezes. As this process continues it backs up under the shingles and finds a way into the attic. From there the water works its way onto attic insulation and drywall ceilings. The story is pretty much the same with roof valleys.

Summarized below are the two main steps to prevent ice damming.

Adequately and Properly Install Attic Insulation One of the key steps to preventing ice damming is to ensure the attic temperature is equal to the outside temperature at all times. Thus it is imperative to prevent warm moist air from the lower living areas of the home to permeate up into the attic. To do this you need to install the proper amount of attic insulation for your climate region. For example, in the New England area R-38 insulation should be used in attics.

Secondly, the insulation needs to be installed properly so that there are no gaps that could allow warm moist area from the below living areas to seep up into the attic.

Ensure Proper Attic Ventilation

The second major step to preventing ice damming is to ensure there is proper attic ventilation. Even with adequate and properly installed insulation there will be some minor moist warm air leakage into the attic. The trick is to remove that warm moist air from the attic as quickly as possible. To do this there needs to be adequate soffit and ridge vents/gable vents installed in the attic. The soffit vents help to enable cooler air to be drawn into the attic. The ridge vents, or gable vents, on the other hand allow warm moist air to rise up out of the attic.

By ensuring proper attic ventilation and air flow you can prevent warm moist air that seeps up from the below living areas to cause any damage during its short life in the attic. The typical rule of thumb is you should have 1 square foot of attic ventilation for every 300 square feet of ceiling area in the attic. Half of the ventilation should be for the soffits and the other half for the ridge vents / gable vents. Also, make sure that attic insulation is not blocking the soffit vents. By following these two steps you can prevent ice damming, or at least dramatically mitigate ice damming in your home. One final note. When you have your roof re-shingled always make sure there are two courses (approximately 6 feet) of Ice and Water shield installed at the roof eaves.

Similarly install Ice and Water Shield in the roof valleys. The Ice and Water shield should extend outwards from the roof valleys by about 18 inches.