When I returned from a midwinter vacation, I walked up to the front of the house and noticed the mother of all ice dams on the roof. A spot that has few problems some winters now sported an impressive hunk of ice and a set of thick icicles, some hanging nearly to the ground.

Something indoors had to have changed during my absence to cause it.

I dropped the luggage at the door, kicked off the snowy boots and proceeded to the second floor. I went immediately to the place in the house near the ice dam and looked for a cause. Then I saw the culprit -- the attic door was slightly ajar.

That was all that was needed to allow warm indoor air to flow into the attic space. The warm air melted the snow high on the roof, the snow melt ran down and then froze again on the cold edge of the roof. In just a week, there was a gigantic ice dam.

I closed the access door and secured it. But that's like the proverbial "locking the barn door after the horses are out." The ice dam has to go, because behind it is snow melt waiting to leak into the house.

Lots of folks have their cherished remedies: ice pick, deicer in hosiery, blow dryer. But this dam needs professional help. I'll call in the roof steamers to safely and quickly melt it away, releasing any water while saving the shingles from harm. It means I'll be spending hundreds of dollars in ice removal instead of thousands of dollars in roof and interior repairs.

Many roofing contractors do ice-dam removal. You can check yellow-page directories or online for "snow and ice removal," "roofing contractors" or "ice removal." Or just call a roofer with whom you have experience.

Be sure to ask:

• How they remove the ice dam; steam is the preferred method.

• If they're insured and how much experience they have.

• If they offer a guarantee.

• How much they estimate it will cost.

In most cases, contractors will need a place to plug in their equipment. They might ask that the homeowner be home while they do the work.

Ice removers are busy now. You likely will have to leave a message for service.

Costs vary. It's always a good idea to call a few and compare prices and services. As an example, Roof-to-Deck (651-699-3504) uses steam to remove ice and snow from roofs and charges $220 an hour with a minimum of two hours.

Remember, you can prevent ice dams by keeping warm air from escaping from your indoor spaces into attic spaces. For information, go to www.extension.umn.edu. Search for "ice dams."

Send your 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.