Q In the past, we've had occasional problems with ice dams and leakage. Do we have to worry this year? If so, what do we do about it?
A Yes, conditions are good for making ice dams, and its partner in crime, attic frost. Combine a load of snow on the roof with a good cold snap and homes can develop either, or both. The results can be stained, bulging walls and ceilings, even water leaking into the house.
Ice dams reveal themselves with long icicles hanging from the roof, or a ridge of ice lurking under the snow at the roof's edge.
Attic frost, on the other hand, often goes unseen until the cold snap is over and the weather moderates. Then the leaking and staining commence. Sometimes water will even drip from ceiling light fixtures.
Ice dams and attic frost have the same root cause: air seeping from the living space into attic spaces.
With ice dams, the warm, moist air from the living space is enough to cause the snow on the roof to melt, running down the roof only to refreeze at the edge, creating a dam. Subsequent melting causes water to back up behind the dam and under shingles, leaking into your house.
Many homes have a strip of rubberlike membrane under the shingles along the roof's edge to prevent ice dam leakage. But if ice dams get large enough, water will breach these protections and leak into the house.
All it takes for attic frost to occur is a good dose of frigid weather. Attic rafters and roof underlayment can get so cold that any warm air from the living space that gets into the attic will condense, freeze and create an accumulation of frost. When weather moderates, the ice and frost thaw and the resulting moisture drips down through insulation and into the house. (Roof vents are supposed to remove this air to prevent frost and dams, but often fail to do that.)
