What causes ice dams?
Ice dams form when melted snow refreezes at roof edges. Three things are required for an ice dam to form: snow, heat to melt the snow, and cold to refreeze the melted snow. The heat from inside the home rises through the ceilings and into the attic. If the attic is sufficiently ventilated, heat is dispersed, leaving the attic area and roof deck as cold as the outside air. Without sufficient attic ventilation, however, heat collects under the roof deck and melts the snow on the roof. Melted snow rolls down the roof slope to the eave and refreezes before dripping off the roof. As this process continues, the layer of ice at the eave gets thicker; eventually causing a "dam" that traps the melted snow behind it and creates a pool of water.
Ice dams can cause different types of damage. If the water from the melted snow continues to flow, the water pools and eventually backs up onto the roof surface. The pool of water can creep under the shingles and into the home causing interior water damage to walls, ceilings, insulation, and other areas. Sometimes the ice dam can cause damage to the roof covering, as well. The water can also continue to re-freeze causing a large amount of ice to build up in the gutters. This build-up can cause a weight problem, collapsing the gutters from the ice build-up.
What to do if you have an ice dam
Large icicles extending from eaves and gutters are often signs of an ice dam. Water coming in through ceilings or windows is another sign. If you have these conditions or to prevent these conditions, you should remove snow from at least the first three feet of the roof with a "roof rake". Roof rakes are available at most hardware stores. Never walk on a snow-covered roof. Make sure you work from a ladder. Never put rock salt or sodium chloride on the roof or the shingles will be damaged. Potassium chloride or calcium chloride can be used safely to melt ice. Removing an ice dam can be quite dangerous. Consider contacting a professional to remove snow and ice from your roof.
Long-term prevention of ice dams
Ice dams can be prevented by controlling the heat loss from the home. Proper ventilation and insulation of the attic are the best ways to prevent ice dams. Keep the attic well ventilated. The colder the attic, the less melting and refreezing on the roof. Keep the attic floor well insulated to minimize the amount of heat rising through the attic from within the house.
Unfortunately, ice dams may be unavoidable if your home has recessed lighting near the roof. Heat generated from these lights melts snow, which then contributes to ice dam buildup. The only sure way to avoid this problem is to eliminate recessed light fixtures near the roof.
Icicles forming on the edge of the roof are a sign of a ventilation problem. If you re-roof your house, installing a water-repellent membrane under the roof covering is an extra precaution you can take to prevent roof leaks caused by ice dams. Talk to your local building official about minimum code requirements for ice dam protection and consult a qualified roofing or insulation specialist for recommendations tailored to your situation.
While it's extremely rare that an ice dam will damage the roof itself, we do see claims for sagging or collapsed ice-filled gutters, water damaged ceilings, peeling paint, damaged plaster, and wet insulation. As with all water claims, it's very important to dry the affected areas as soon as possible to avoid water-related complications.
On a typical Home and Highway® policy, damage to the structure is covered unless specifically excluded or limited in the policy. There's no exclusion that applies to damage caused as the result of an ice dam, so the costs associated with remediating the interior water and repairing the damage would be covered.
Personal property is covered only against the specified perils in the policy. Damage caused as the result of ice dams is not one of the specified perils, so damage to personal property is not covered unless specific coverage is added to the policy. Be sure to talk to your independent insurance agent about the coverage on your homeowner’s policy.