What is an ice dam? Ice dams are caused by heat rising from the interior of a building, warming a snow covered roof's surface enough to melt the layer of snow nearest the warm roof. The melted snow flows down the roof slope toward the gutters at the edge of the roof. At the edge of the roof, where there is no heat from the building, the water chills and freezes. The gutters and downspouts clog with ice and an "ice dam" forms at the edge of the roof in the gutters.
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 water will find its way into the building, causing interior water damage to walls and ceilings. 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.
Ice dams indicate heat loss. An ice dam can indicate that too much heat is escaping through your roof. Ice dams form when a too-warm roof surface causes snow to melt as it falls on the roof, even when the surrounding air temperature is below freezing. Since the source of this heat comes from inside the house, the eaves of the roof are invariably colder, since they don't have a warm room underneath.
Once an ice dam forms, the potential damage can be serious. Take these steps now to avoid trouble later:
- 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.
This two-step approach decreases the likelihood that ice dams will form or, at least, reduces their size.
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.
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.