Ice Dam Cometh: How to Prevent Ice Dams on Your Home

By: Joe Truini

Ice on a home roof

If you’re fortunate enough to live in the Sunbelt or some other balmy region, chances are you’ve never heard of—or at least experienced—ice dams. I, on the other hand, live in New England, so every winter ice dams are as common—and as welcoming—as frostbite and sub-zero temperatures. That’s because ice dams can be destructive, problematic, and virtually impossible to remove once fully formed.

Ironically ice dams are often responsible for one of the most beautiful and iconoclastic of all winter images: glistening, crystal-clear icicles hanging from gutters and eaves. Heck, even I marvel at the delicate beauty of icicles, but only when they’re hanging off someone else’s house.

Here’s a brief explanation of how ice dams typically form: It all starts with a roof blanketed in snow. The snow layer that is sitting directly on the roof begins to melt, and water runs down the roof underneath the snow. When the water hits the overhanging eave of the house, it begins to freeze. Some water often drains into the gutter, where it freezes as well.

As the snow continues to melt and water freezes at the eave, ice eventually builds up along the roof forming a thick ridge or dam. Then, as water runs down the roof, it’s blocked by the ice dam, and forced up under the shingles. I know this seems to defy all laws of physics (and commonsense), but water will actually flow up the roof, working its way under the shingles. And that’s where the trouble really begins, since roofs are designed to shed water running down the shingles, not up.

Over time the water will work its way beneath the shingles and the underlayment, and into the seams between the plywood roof sheathing. From there, water drips directly into the attic, where it soaks through the insulation and ceiling, before dripping into the room below. If not detected immediately, the damage can be very difficult and expensive to repair, especially if it ends up ruining the floor, walls, or furnishings.

Now, the above explanation is a rather simplified version of how ice dams form, the science behind this phenomenon is much more complicated, but if you go back to the very beginning, you’ll find a clue to solving this problem. The entire process starts when snow sitting on the roof begins to melt. That’s key because ideally you want the interior attic temperature to be as close as possible to the outside air temperature. That’s why there’s only insulation on the attic floor, not between the roof rafters.

However, if the attic floor isn’t properly insulated or if heated air is leaking through the ceiling, via cracks, crevices, ductwork and light fixtures, then the attic will become warm. And it doesn’t take very much heat to raise the attic temperature enough to melt the snow on the roof. Since the overhanging eave extends past the house, it remains cold, which is why the water freezes when it hits the eave.

So, what can you do to prevent ice dams on your home? Try these ideas:

  1. Seal Air Leaks: Use caulk, insulation and weatherstripping to seal all upstairs ceilings to stop heat from flowing into the attic.
  2. Add Insulation: Measure the depth of the insulation on the attic floor, and add more, if necessary. Call the local building inspector or licensed contractor to find out how much insulation is required in your area.
  3. Attic Ventilation: Check to be sure that the attic ventilation system is operating properly. Most homes have soffit vents and ridge or gable-end vents, which allow air to flow into the attic along the eaves and out the attic at the ridgeline or gable walls. Be certain the attic-floor insulation isn’t blocking the soffit vents. And never staple plastic or anything else over attic vents. Remember, you want attic temperature to be as close as possible to the outside air temperature.

If your home already has ice dams, there’s not too much you can do about them. Avoid installing electric cables or any other device to melt the ice, as they won’t solve the problem. You can try using a snow rake to remove as much snow as possible from the roof. That’ll at least remove the source of water. Just be sure to work safely from the ground, since it’s never a good idea to climb onto a snow-covered roof.

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13 Comments on “Ice Dam Cometh: How to Prevent Ice Dams on Your Home”

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  • kathy morano Says:
    February 9th, 2015 at 10:06 am

    ice dam on roof at bottom of shingles about 4 inches thick and 4 inches wide.. I have removed the gutter and use roof rake to clean the roof off.. but I am still getting water into my bow window.. how can I get this ice off the roof to stop the leak without contacting professional contractor as we are living on social security and have limited income..is it safe to use ice melt ?? when the temp gets to be about 30 degrees that’s when the problems start.. PLEASE HELP.. thank you for your time



  • Ana Says:
    December 1st, 2014 at 6:12 pm

    Lee,
    what type of salt did you use to keep it from freezing? My neighbors have ice shows every winter, and most are elderly, although maybe insulation would help too.
    Thanks.



  • Ana Says:
    December 1st, 2014 at 6:08 pm

    Hi, Joe T.,
    Where online did you purchase the roof rake, and how long is the reach of the roof rake?
    Thanks.



  • Mary greenwood Says:
    November 30th, 2014 at 11:41 am

    We replaced our roof and added insulation in the attic but still get ice dams at the soffits.. There were’nt any baffles so we added some but that hasn’t helped. .I noticed that the lousier have been covered with siding is this the reason? We added a roof ridge when we replaced the roof. HELP!



  • Lee Nuzzo Says:
    November 29th, 2014 at 9:17 am

    I have used a snow rake the past 10 winters with great success, but prior to using the snow rake I have had ice dams . The ice dam caused water to leak into my kitchen windows and wall. I cut the legs off of pantyhose and filled the legs with granular salt, tied off the open ends of the leg section and left a 10′ long rope handle. I toss the filled leg a few feet above the edge of the roof. Then I pull the rope handle to position the filled leg perpendicular to gutter to melt a narrow trough for the water to travel off the roof. I also placed a small salt filled leg section on the gutter right above the downspout connection. Thought this worked in an emergency to avoid major damage to the wall and windows. Never miss the show, great content.

    Lee Nuzzo Crown Point, In


  • Official Comment:


    Joe T. Says:
    February 14th, 2013 at 12:51 pm

    Hi Tim, I am not familiar with insulation costs in Ohio, but it’s typically cheaper to buy fiberglass batts and lay them down yourself, as opposed to renting a blower and buying blow-in insulation. Of course, as you mentioned, it is much more work to cut and lay down each individual batt than to simply blow in the insulation. Regardless of which type of insulation you install, be sure you don’t block the air flow from the soffit vents, assuming you have soffit vents. It’s important to allow fresh air to enter the attic at the eaves and exhaust out the ridge vent or gable end vents. Sorry I couldn’t be of more help. Good luck.—Joe T.


  • Official Comment:


    Joe T. Says:
    February 14th, 2013 at 12:45 pm

    Hi Patricia, I feel your pain. I live in Connecticut and we’ve gotten a ton of snow this winter–with more to come, I’m sure. Glad you liked the article on ice dams. Increasing attic ventilation is key, but it’s also helpful to remove snow from the edges of the roof with a roof rake. I bought a roof rake online that has an extra-long handle, which allows me to pull off the snow while standing safely on the ground. Good luck, Patricia and hang in there, spring is coming!–Joe T.



  • Tim Helsel Says:
    February 12th, 2013 at 8:08 am

    Hi, can you tell me the better choice for insulation in the attic?
    My brother is pushing me towards blown in, where we buy the packages and get the blower from the home store. Sounds easy, less stress on us to crawl around placing rolls or batts in the attic.

    I think we lay down our exacts with rolls or batts, meaning I buy R30, lay it down and there we go,

    I can not tell price-wise which is saving me money. My sq ft is 910 I need covered, any help is very much appreciated

    thanks, tim helsel in Ohio



  • Patricia Kelly Says:
    February 11th, 2013 at 10:16 pm

    We have just survived the Great Blizzard of 2013 here in R.I. and today it is raining! Thank you for your great article on ice dams & how to prevent,plus your information on insulating the attic. Plan on being very busy; can’t wait for spring.


  • Official Comment:


    Joe T. Says:
    January 3rd, 2013 at 2:22 pm

    Hey Tim, Glad you like the website and found the information on ice dams useful. Hope all is well in Grove City. As you mentioned, the lack of attic insulation is likely the main cause of your ice dams. And when you do add insulation, be sure you don’t place it in too close to the eave. You must leave space for outside air to flow through the soffit vents, up between the rafters, and out the ridge or gable-end vents. Maintaining an efficient attic-vent system is the best way to combat ice dams. Thanks for writing and good luck!–Joe T.



  • Tim Helsel Says:
    December 31st, 2012 at 5:51 pm

    Thanks for providing great information for us home owners. We just moved into a 40 year old home with lots of leaks. I noticed today the ice dam on and around the gutters. I know we lack enough insulation. I have watched the other videos on how to instull and how much. I think I am not ready to tackle this job. Appreciate the easy and simple use of this website too. blessings from Grove City Ohio


  • Official Comment:


    joe t. Says:
    January 23rd, 2012 at 9:45 pm

    Dear Gloria, I’m sorry to hear about your roof leak. Flat roofs are notorious for leaking, which is why you see very few of them. The first suggestion is to please keep your husband off the roof. That’s no place to be, especially when it’s wet and/or covered with snow and ice. It’s hard to give specific advice without seeing your roof, but I suspect it doesn’t leak during a rain storm because the rain runs off. But snow and ice sits up there and melts slowly, where it gets a chance to seep through seams and joints between the copper roof panels. The problem isn’t with the roof itself, but the way it was installed. Any roof system will leak if improperly installed or damaged. Your only option is to call a professional roofing contractor and have them inspect the roof for punctures or ill-fitting joints. The contractor should also closely inspect flashing or vent pipes, if there are any. Another common place for leaks is where one roof meets another roof or the side wall of the house. Sorry I can’t be more specific, but an experienced contractor will certainly be able to locate and fix the leak. Thanks for writing and good luck.–Joe T.



  • Gloria Says:
    January 23rd, 2012 at 2:33 pm

    We have a flat roof only over my office in our home.We had a leak so we had a copper roof put on they said it will never leak,guess what it does and the roofing compancy will not do anything about it. It only leaks when it snows or when ice melts then it come from the celing and drips into my office.It’s a ice dam. We have know attic its just a flat roof.My husband has gone out on the roof and shovel the ice off he can’t keep doing this he is 71 years old.
    What can we do next if anything?
    We do not get your show. so can you email me and tell us what to do if anything.
    Thanks


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