Roof killers—icicles and ice damming


I touched on insulation and air-sealing in a few recent posts. And as happens in the winter, we’ve noticed a big increase in the last few weeks on people asking about icicles and ice damming. It’s probably time for a quick refresh and retread of an earlier post.

What is Ice Damming?
Big icicles and ice dams are typically caused by poor or missing insulation and air leakage from your house into your attic.  In the winter, this warms the roof and causes the snow to melt. The melting snow then moves down the roof slope until it reaches the cold overhang, where it refreezes.

The process forms icicles and can actually create a dam that eventually forces the water to back up under the shingles and sometimes into the ceiling or wall inside the home. In addition to roof and water damage, ice dams can cause structural decay and mold and mildew to form in attics and on wall surfaces. 

Big icicles are a good sign of too much heat loss through your attic.

Big icicles themselves, like those shown here, are obvious signs that you’re at risk.

But snow melt patterns can also indicate a problem of too much heat loss. In this photo below, you can see snow melting off the roof at different rates, driven by heat loss from the house. 

roof snow melt patterns

Uneven snow melt also is a sign that something is awry

And in the townhouse complex below you can see the building that GreenHomes treated with even snow still on the roof—a sign the building isn’t losing energy rapidly. Conversely, you see the untreated building with the snow melted–a sign that it’s losing a lot of energy. No big icicles this time—but had it been a bit colder, the melting snow would have refrozen at the eaves and created big problems.
treated townhouse retains heat
The townhome treated by GreenHomes loses heat more slowly through the attic and thus snow melts slowly and doesn’t accumulate as ice out at the eaves.


a leaky and poorly insulation town home attic melts snow quicly

This town home has not been treated and the wasted heat melts snow quickly. In the right temperatures, the melted snow would refreeze and create ice problems--bad news. And in any event, this folks in this building are spending a lot more on energy than they should.

The Fix
Fortunately, you can dramatically reduce damage from ice damming by sealing the holes connecting your heated living space and the attic, as well as properly insulating your attic. There are different techniques to stop air leaking through recessed lights, leaky heating ducts, attic access doors, and plumbing and electrical penetrations. Sealing these leaks keeps warm air in your house were it belongs. Together, with adequate levels of insulation, this greatly reduces the chance of ice damming and large icicles.  You do NOT just want to add more insulation before sealing the air leaks—this can actually create additional problems that can also damage your roof. 

It’s important to not that you can’t eliminate icicles completely.  Small icicles are normal.  And some roof architecture–especially big valleys draining to a small corner–are especially challenging.  But if you have long icicles or thick heavy ice you should act quickly to prevent damage.  (And this means preventing the ice from forming in the first place, not risk life, limb, and your roof trying to chip off ice that’s there.)
 Do it right.  Find the important leakage points and seal them up.  Then add a lot of insulation.  And afterwards, as with any time you change the way your house works, have your combustion appliances tested to make sure they’re operating safely and efficiently.

An added benefit to this, of course, is you’ll save energy, save money, and be more comfortable in your home, too!

Save the ice for your holiday cocktails!

[Update, see more roof melt and icicle photos.]


P.S.  The added insulation can qualify for the $1,500 federal credit.  Save money while you save you roof!

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18 Responses to “Roof killers—icicles and ice damming”

  1. Air leakage–even the small cracks add up « GreenHomes America Says:

    […] the small cracks add up By greenhomesamerica We continue to get a lot of inquiries about ice dams–especially now that snow has started hitting our Northeast […]

  2. hurricane heroes Says:

    there are many solutions to avoid this things. it is much better to contact a reputable roofing contractors. also make sure your home has a home warranty. so that damage repair maybe covered by the warranty.

    • greenhomesamerica Says:

      It’s important to remember, ice dams and icicles are the symptom of the problem–too much heat loss. Roofing alone won’t fix the problem, and addressing outside ice doesn’t mitigate condensation and even ice formation INSIDE the attic. While you may need new roofing, you want to first address underlying problems–poor air-sealing and poor insulation–before throwing money into a new roof. We run into too many instances where people replace roofs hoping to correct the problem only to have the roofs failing after a few years. Warranties and insurance only get you so far–and rising premiums or cancelled policies aren’t fun either.


  3. Snow in Northeast creates conditions for roof icicles and ice damming—signs of wasted energy « GreenHomes America Says:

    […] snow much of the last ten days and more on the way. Snow on rooftops often leads to problems with icicles and ice damming, as we’ve discussed here before, but primarily for homes with air leakage into the attic and […]

  4. Icicles Follow-up « GreenHomes America Says:

    […] you can’t effectively eliminate heat loss or icicle formation.  But with proper  insulation and air-sealing you can greatly reduce the problem, save a lot of […]

  5. DC and the Mid-Atlantic Snow Leads to Roof Ice Problems « GreenHomes America Says:

    […] seaboard are covered in a blanket of snow.   Snow on rooftops often leads to problems with icicles and ice damming, as we’ve discussed here before, but primarily for homes with air leakage into the attic and poor […]

  6. m.Austin Says:

    Once the icicles have formed on your house should you try to knock them down for leave them alone. we have many and they are very large ,we’re not sure what way to go. Thank you

    • greenhomesamerica Says:

      Knocking them down can be very dangerous–they can wiegh hundreds of pounds. And you can rip off gutters and fascia and damage you roof trying to remove them. If they are in a location where there won’t hurt anything when they fall, I would leave them. And don’t allow children or pets in the area. Can’t really give specific advice without seeing the particular home and situation.

      Another issue you might have is water building up behind the ice. See the post at for some suggestions.

      And take this as a wake up call–there are preventive measures that you can take to prevent this is the future and save money when you stop wasting energy through the attic.

  7. DIY—Do it yourself attic insulation and air-sealing « GreenHomes America Says:

    […] With winter still hammering parts of the country, the mid-Atlantic states being plagued by ice dams, and people being interested in good home economics in today’s tough national economy, a lot […]

  8. Ron Says:

    After 20 years of living in a home with minimal 6 ” attic insulation and one attic vent- we blew in cellulose insulation on top of the reg. insulation to create approximately 24 inches of insulation. We also got a new roof (includes 6 feet of ice guard) and ridge vent. Now…for the first time in 20 years, we have major icicles all along our roof line. The roofers also installed gutter helmet guards from HomeDepot. Obviously, we did something wrong.
    But what?

    • greenhomesamerica Says:

      It’s hard to diagnose a house from a distance, especially with a short paragraph description. You mention adding insulation and roof ventilation. But no mention of air-sealing. Did this happen before adding insulation. Search on “air-sealing” here and you’ll learn more about the importance of this. We have seen cases where adding roof ventilation without air-sealing the attic plane actually lead to more heat loss into the attic, and a warmer attic than prior to the roof ventilation. Why? It’s possible that the roof ventilation exacerbation the leakage and heat loss into the attic. If air-sealing wasn’t a part of your insulation package, it’s not too late. (Although it will now be more difficult and expensive as the deeper insulation must be moved around.) Note, some weather conditions and architectectural details will lead to icicles in even a well-sealed and insulated home. However, that doesn’t sound like it’s the case here.

      As an aside, I’m not familiar with the particular “gutter helmet guards”, but I’m generally not a fan of these types of products. I prefer up-sizing to commercial gutters and downspouts in most residential applications.

  9. home sweet home Says:

    Thanks for share dude.

    can you show me where I can buy high quality roof for my home? may be you know the roffing online store. thanks before

  10. Vent those bath fans to the outside–NOT into the attic « GreenHomes America Says:

    […] your bath fan into the attic—with all that warm air—is a recipe for ice dams (and more on ice dams).  Don’t do it! Please don't exhaust your bathroom fans into the […]

  11. Syracuse pounded by snow–and roof ice problems follow « GreenHomes America Says:

    […] discussed earlier about how poor air-sealing and insulation can lead to ice problems.  And we’ll renew that conversation.  Bottom line:   While nothing can totally prevent […]

  12. Catherine Says:

    I am wondering how to prevent ice damming and icicles when you have a finished living space in the attic. What is the proper way of keeping the roof cold when the attic is used as a living space and is open to the rest of the house. I haven’t been able to find much information on this topic.

  13. Jason Todd Says:

    Hi Catherine, Making sure that your roof, as well as your home, are properly insulated and air sealed is the ticket. There is information on our website, and also at This quote comes from the Home Performance with Energy Star website: “Hire a contractor who is an energy specialist or specializes in air sealing to do an in-home evaluation. A good specialist will use diagnostic equipment to evaluate the performance of your home and generate a customized list of improvements.” Unfortunately, there may not be a do-it-yourself solution, but a good Home Performance contractor can certianly help!

  14. roof renevation Says:

    If you are actually in Roofing you recognize that there’s a lots of recourses which might be complete nonsense, luckily your website is not one of these sites, i like your content a lot, keep up the good work

  15. Marla Says:

    Good web site you have here.. It’s difficult to find high quality writing like yours nowadays.

    I seriously appreciate people like you! Take care!!

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