Posted by: SherlockHomesSY | 14 Jan 2011

Common Complaints: Ice Dams

Ice Dam

(C) Tom Fieza, Mr. Fix-it


As I write this post, I’m in Evanston, WY on New Year’s Day.  The streets are covered with crunchy snow and huge icicles hang off the roof, over the eaves.  As I ponder, I wonder whether the icicles are there because it rained before it started snowing—or something worse, ICE DAMS!

What is an Ice Dam? Only those who live in places where it snows need to worry about ice dams.  They form on eaves, over exterior walls.  Warm air escaping into the attic through the ceiling thaws snow, which runs toward the gutter.  Then it freezes.  The process starts over, except this time the water encounters the ice so it backs up under the shingles.  Only now, water leaks into the soffit or on to the ceiling!

Damage. Below the ice dam, wood framing is rotting and insulation is soaked.  If you’re lucky, you’ll see water stains on the ceiling.  For some folks, it’s obvious—water is leaking into the house!  Mold is not far behind, if not there already.  It’s time to put catch pans under the leak and wait for warmer weather—unless you’re prepared to work in a cold attic or live with cold air in the house while fixing it.

Culprit Profile. Ice dams occur because the attic gets warm enough to melt snow.  How? One or more of the following four ways: insufficient insulation, air leaks, vents blowing into the attic, or inadequate ventilation.

To create ice dams, just add snow—particularly the kind that hangs around awhile.  Light snow adds an insulation blanket to the roof, about R-1 per inch.  The more snow, with any of these four issues, the warmer the attic gets.

Goal. The goal is to keep the attic temperature the same as it is outdoors.  The solutions are to add insulation, seal air leaks in the ceiling and any ductwork, vent bath area fans and rangehoods outdoors, or increase attic ventilation.

Temporary Relief. It’s not convenient, and perhaps not advisable, to fix the problem until spring.  After putting drip pans under the leaks in the attic, consider dealing with the snow on the roof.  Watch out for avalanches and falling icicles.  Also, don’t damage the roof. Did I mention not to get on the roof?

One way is to remove the snow from over the eave.  My friends in cold country recommend a snow roof rake.  Try your local building supply store?

Another way is to drain the ice dam by creating drain channels.  The suggestion is to put snow melt chemicals (not rock salt) in panty hose.  The sock is laid along the slope, just below the ice dam.  The water should drain.

Whatever you do, don’t use electric snow & ice melt cables.  Besides not being good to look at, they require more holes in the roof!.

Roof Damage. I got to see the results of ice damming first hand in Iowa last summer.  The asphalt shingles were a mess and roof deck was rotted through.  Roof repair is required.  Generally, an ice shield should be installed along the down-slope side of the roof—full length.  The roll is 39 or more inches wide—wide enough to more the cover the eave.  Ask a roofer!

Fixing Ice Dams. A weatherization contractor can air seal a ceiling and add insulation.  A roofer can add ventilation.  For roof pitches over 6/12, the building code formulas don’t work, so seek out the services of a roofing consultant.  Roofers know what to do when a vent needs to go through a roof, but an HVAC contractor or handyman may need to get it there.  Some home performance contractors can do the whole job—and test out afterward to ensure the house is still safe to live in after air and duct sealing.

If mold is a significant issue, a certified mold remediator can remove it.


Mr. Fix-It, Tom Feiza, has an owner’s manual for your house, How to Operate Your Home.  Chapter 30 of the 2nd Edition was a source for some of this article.

Our home performance website covers air sealing, duct sealing, insulation, and mechanical ventilation.  Future blog posts will cover attic ventilation.

In Conclusion

I’m looking forward to getting out of the frozen north after spending the holidays here.  The last article in the Common Complaints series is peeling paint.



  1. Electric heat trace cable, like those provided by Delta-Therm are the way to solve this issue. But let the experts (Systems Plus LLC) design the systems for your, to ensure that you have a proper design for your particular application.

    • Are they like to serve the average homeowner? All the pictures I saw on your site are for commercial buildings. My concern is that this solution is cost prohibitive by this company.

  2. It all depends on the cost, how often do you get ice dams…most often getting a roof rake will solve the problem. If you are going to buy a electric melters and other things they all cost a lot of money. I would suggest using a roof rake or calling a local ice dam company to remove them. They will be able to give you advise on if this is a one time fix or the proper solutions on getting it fixed long term with better insulation and other tips. Just my suggestions from Minneapolis Ice Dam Removal

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