Ice damming occurs when rooftop snow melts and then re-freezes near the eaves, creating an obstruction to proper water shedding. Melt water then begins to pool and can seep underneath the shingles causing massive water damage.

The solution to this problem is two-fold:

1. Prevent radiant heat loss from conditioned spaces to attic
2. Keep the attic cool by providing adequate ventilation

The best way to ensure your attic stays cool (and also good for your energy bill) is to prevent radiant heat loss to your attic by providing adequate thermal insulation, whether it be blown-in loose fill, fiberglass bat or spray-foam.

The effectiveness of thermal insulation is measured by its total R-value. All insulation has printed on its package its R-value for a particular installed thickness. In Wisconsin, my state, it is recommended to have an R-value of at least R-49 and as high as R-60.

There are, of course, other causes of heat escaping into the attic, and one of those is hot air (convection heat loss). This occurs when there is an inadequate vapor barrier between the attic and the conditioned space below. Fiberglass bat and blown-in insulation do little to prevent this type of heat loss. It's difficult to install a vapor barrier in an existing structure because it is typically installed between the studs/joists and the drywall. However, an effective vapor barrier can be achieved by applying a layer of closed cell spray-foam insulation between the joists. You can then apply blown-in or fiberglass bats. If using bats, you should apply them in layers in a criss-cross pattern.

Hot air can also be introduced into the attic from other sources, such as leaking or disconnected ventilation and/or heating ducts.

Your final defense in keeping our attic cold is to make sure you have proper ventilation. Because hot air rises, it is necessary to create a chimney effect in your attic by providing adequate ventilation at the eaves and the ridge.

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More aggressive air movement can be achieved by using powered attic vents in addition to your eaves and ridge vents.

If for any reason you are unable to prevent ice damming by applying these remedies, there is one other defense against ice damming that is really only a bandaid and does nothing to fix the underlying problem, and that is installing heating cables near the eaves of your roof. But these heating cables waste energy (in addition to the energy you're already losing to your attic) and should only be used as a last resort to protect your home from ruin.

Ice damming is one of the leading causes of water damage insurance claims, and you can avoid this catastrophe by checking your attic today.

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