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.)

The solution is the same for both problems: Stop the air movement. Seal the living space from the attic spaces so no (or very minimal) air moves between them. Then, if necessary, consider adding more attic insulation or ventilation.

You can do the job yourself, but consider hiring a contractor, specifically a weatherproofing or insulation contractor. Not every contractor knows the latest techniques for preventing ice dams and attic frost. Be sure the insulation contractor will seal the leaks before adding insulation or any necessary ventilation. Just adding insulation or ventilation is not the answer; the air leaks must be closed.

Try to get a contractor who uses infrared or a blower door to first show where the leaks are, and then that they've been sealed. To find contractors, check yellow-page directories under "Insulation contractors" or contact the Minnesota Building Performance Association (www.mbpa.us).

Minnesota offers free information to help you seal these leaks yourself or to help you make sure you get your money's worth from any contractor you hire. Go to www.energy.mn.gov and type "attic bypasses" and "ice dams" into the search box. For written copies, call 651-296-5175 or toll-free at 1-800-657-3710.

For an existing ice dam

• Gently remove some snow above the dam with a roof rake. But do not clean down to the shingles. Be aware that roof raking often damages the roof, shortening shingle life. A rake on wheels or a similar device is best. (Check hardware or home improvement stores.) Do not go onto the roof and shovel or hire anybody to do that.

• If you do hire help, contact a roofing contractor, preferably one who uses steam. It's fast and safer for roofs. If methods other than steam are used, get a written guarantee that they won't damage your shingles or roof. Get several bids and check references.

• Some people use sidewalk deicer to melt a drainage channel in the ice. Be careful to use deicer formulas that won't damage gutters and downspouts or plants near your house's foundation.

Send questions to Fixit in care of the Star Tribune, 425 Portland Av. S., Minneapolis, MN 55488, or call 612-673-7032, or e-mail fixit@startribune.com. Past columns are available at www.startribune.com/fixit. Sorry, Fixit cannot supply individual replies. Fixit appears every day except Friday.