Publications by New England Metal Roof

How to Prevent Ice Dams on your Roof

Are you feeling the cold from the so-called polar vertex, yet? Well, it seems like everybody in the US is feeling the cold, with many places experiencing heavy snow fall and residents battling the unsightly ice dams forming on the roofs of their homes. :(

By virtue of being involved with metal roofing and roofs in general, I am often asked for advice on “how to stop ice dams from forming on the roof?”. So, rather than answering individual questions, I decided to write this guide for homeowners who are looking for simple ways to prevent ice dams in the first place.

roof-ice-dams

What is an Ice Dam?

Before we begin, let’s define an ice dam, and examine how it can form on the roof. An ice dam, is literally a wall of ice that forms on the outside edges / eaves of a sloped roof, and in the gutter. The wall of ice prevents the melted water (the warm air rises up in the attic and melts the snow), to properly run down and drain off your roof. The wall of ice causes melted water off your roof, to rise up underneath the shingles and leak inside your home causing massive damage to your home’s ceilings, dry-walls and insulation. The water damage caused by ice dam leaks can also cause mold growth and rotting of the wood structures affected by the water leaks.

What causes Ice Dams?

What causes ice dams on my roof, and how does an ice dam form? The mechanism of an ice dam formation is best explained by poor insulation, and ventilation of the building’s attic. When the attic is poorly insulated, the warm air from inside the building escapes through the attic and rises up to the peak of the roof, where it warms up the roofing surface, which melts the snow seating on the roof. The snow begins to melt and melted water runs down the roof slope, underneath the blanket of snow. When it reaches the eave of the roof, it begins to refreeze again forming a wall of ice, which turns into an ice dam.

As you can see in the picture above, the upper portion of the roof is exposed as the snow has melted, and water ran down, and turned into an ice dam, that looks rather extreme! The reason, for the exposed roof shingle, is that warm air that was rising up in the attic, reached the highest point in the attic where it transferred the warmth to asphalt shingle, which in turn has caused the snow to melt on top of the roof. When the melted water reached the edge of the roof, which was not as warm as the top, the water refroze forming icicles and ice dams on the edge of the roof. As you can see, the mechanism of ice dam formation is not external, but rather internal, and has to do with inadequate insulation and ventilation of your attic space.

Steps to Stop Ice Dams:

Clearly an adequate insulation is the key in preventing ice dams from forming in the first place. As long as, we can find a way to keep the warm air inside the house, and stop it from leaking into the attic, we can stop the ice dams from happening. Thus, we have to find a way to properly and fully insulate our attic.

Attic Insulation

For most roofs located in areas with snowfall a minimum of R – 49 insulation value will be required. If your home is 30 years or older, than chances are that it is not properly insulated, and you will improve the energy efficiency and functioning of your home by upgrading your insulation to R – 49 value. So if you have an older home, you will first want to find out how much insulation you already have. An easy way to measure your attic floor insulation is by measuring its thickness, which you can measure with a simple ruler, and then multiply the thickness in inches by 3.14. This will give you the approximate R-value. Thus, if you have six inches of Fiberglass blanket insulation, you will get; 6 x 3.14 = 18.84. which means that you need to get an additional 10 inches of attic floor insulation for your home to meet the Department of Energy Requirements.

Refer to to Energy Star’s recommended levels of insulation table to determine the proper R – value for your geographic zone.

A word of caution:

If your home has become a victim of an ice dam formation, and you consider adding additional insulation to your attic, stop right here, and first check for any major air leaks and drafts in your attic, ceilings and in between the walls before you add any more insulation. Properly sealing the leaks in your attic, will play a major role in helping you prevent the ice dams. Take time to identify and locate air leaks in your attic and seal them with caulk, spray foam, or weather stripping. This will make your attic more energy efficient. You should not add any more attic insulation until you have completed this step first.

You can bring up your home’s insulation to sufficient level, once you have taken the necessary measures to check for loose air leaks into your attic, and properly eliminated them.

When buying insulation materials, be sure to choose energy star rated products, which by the way, qualify for energy efficient improvements, and can earn you governmental tax credits in 2009-2010. Also, consider insulating walls, and windows in your home, which will further increase energy efficiency of your home. Doing so, will make your home cooler in the summer, warmer in the winter, as well as help you prevent the ice dams built up.

Attic Ventilation

Once your attic is properly sealed and insulated, it is time to examine attic ventilation. Ideally, you will have sufficient soffit vents, which will allow for air circulation aimed to remove warm air from the attic and bring the cold air from outside. Remember, as long as we can keep our attics, cool, we can prevent warm air from rising up and warming up asphalt shingle, which melts the ice and causes water to run down the slope underneath the snow pack. A home energy contractor can advise on appropriateness of your attic ventilation and recommend adding additional ventilation measures to your home.

Can a Metal Roof Help Prevent Ice Dams?

As one of the best methods to deal with ice dams problem here in the snow country is to use standing seam metal roofs. This will be especially useful if other methods cannot be used for various reasons or are ineffective. Standing seam roof will let the snow simply slide off the roof, and ice dams won’t be able to form. Even if ice dams do form, for example if there is a snow retention system in place, the single-piece standing seam panels will not be vulnerable to any water back-ups as it is the case with asphalt shingles.

Check out how a standing seam metal roof is installed:

Please share your successful attempts in preventing ice dams, and feel free to ask any questions you may have!

14 thoughts on “How to Prevent Ice Dams on your Roof

  1. Greg

    Excellent article, as was the one that lead me here that I found on blogspot.

    I have a metal roof, the most complicated portion of which comes together directly above our main entrence way.

    Basically, the house consists of two triangles — ^ — that intersect each other perpendicularly, one slightly taller than the other.

    Where the two triangles intersect in the front of the house, there is a lower, flatter, porch roof that overhangs our front entrance.

    Most of the roof sheds snow beautifully, but the flatter porch roof — which is over an open-air porch — does not. Making matters worse, snow and water pour from both pitched roofs onto the porch roof, particularly over the entry way, and huge, dangerous ice and snow dams build up.

    Any suggestions on how to deal with this problem?

  2. Roofing Wiz

    Hi Greg,

    Thank you for your feedback.

    I have seen similar architectural design flaw in Swimming pool building of Brown University, All the snow would slide down the middle from both sides, and eventually it caused a huge dent and a leak in the middle of this very expensive and custom designed metal roofing system. So you are not alone.

    Now one of the things you could do, is have snow guards installed on the sides of the metal roof, where the snow slides down the middle of the roof. By doing that you could slow down some of the snow from coming down. Another solution is to pay a roofing company to clean the snow of the flat roof every time it snows. It is expensive and may be your last resort. Now, the question I am asking myself is why does the snow that falls on the middle portion melts underneath the snow pack, which causes your ice dams. Are there some warm air leaks on the sides of the roof that is in direct contact with the fallen snow? Perhaps, finding the sources where warm air escapes in the attic, or through the walls and warms up the snow, and insulating those places so the warm air cannot affect the snow that gets piled up on the flat portion can be a long term fix. That, and the snow-guards on the side to slow down the onset of snow tumbling down can reduce the impact of the snow that melts on that flat roof. If you send me some pictures I might be able to provide more info to help you resolve this problem. Also, I would recommend checking your attic for proper insulation, because it may be that the melted water is coming down from the metal roof and when it reaches the flat portion, it refreezes and forms an ice dam. So if you can insulate and ventilate your attic space, then you might be able to completely solve your problem. Hope this helps and Good Luck,

    Alex

  3. Curran

    Hi,

    Funny you should mention the pool roof at Brown (my alma mater). :)

    We have less of an ice dam problem and more of a melting asphalt shingles problem… but I believe it is the same problem (incorrect insulation/ventilation). Our home faces south and has a gambrel roof with an attic crawl space between the dormer windows. Fiberglass insulation was installed under the roof decking. The second summer after we moved in, the shingles started softening and tearing themselves off the steep part of the roof. So we removed the insulation (insulated the floor and walls of the crawl space instead), but it still gets roasty toasty in there. We would like to ventilate that space with soffits + vents into the proper attic (over the bedrooms) but have been stymied by a 1×6 or 2×6 that runs the entire length of the house, at the angle where the two roofs meet. Because it is the front of the house, I’d rather not install mushroom vents.

    Is this the kind of modification that would require removing the roof decking to fix? I hate drilling blind. We are going to have to replace the roof anyway as the shingles are quite literally fried.

    Curran

  4. Roofing Wizard Post author

    Hello Curran,

    If you simply want to ventilate the space so the shingles do not melt, you would have to install a water-tight horizontal exhaust vent along the entire length of the house. This vent would have to be installed just under the pitch change line, so the water would not get in.

    This should improve ventilation, but may not be sufficient to have shingles last as long as they are supposed to – they will still fry, but not as rapidly.

    Additional drawback of this method is that the cold air in the winter will enter your home … or vise-versa, warm air will escape. But the effect will be the same – you will spend more on heating as there will be cold air inside your walls.

    Best thing in my mind is to install a metal roof which would reflect most of solar heat anyway, and you won’t have to ventilate this space, so heat loss will be minimal. The GAF DeckArmor underlayment will help the wooden deck breath, without much air circulation.

    Since you will be replacing the roof anyway, the costs will be not too far off if you go with a cool metal roof instead of shingles with exhaust vent.

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  7. Bill Bradley

    Hi, I am a retired builder from Northern Australia and we use metal roofing a lot. The ice dam is not a thing that we have to consider as I live in the tropics, but it is always great to hear see how the rest of the world does things. Good informative article Greg.

    For anyone considering metal roofing, bear in mind that the new methods of fixing steel roofing make it the most cost effective HIGH WIND resistant roofing material available today. If you just happen to live in a hurricane area, well have a look at this page if you are interested.
    builderbill-diy-help.com/roof-sheeting.html

    Cheers
    Bill

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  9. greg

    Hi, my north facing roof is susceptible to ice dams due to its low pitch (3 in). I have added insulation to the attic space. I have vinyl siding and a soffet and ridge vent ventilation. I made sure when the siding was installed that I had maximum air intake at the soffets by removing all the plywood on the underside of the over hang.

    I read about ventilation, but doesn’t it make sense that when enough snow falls on the roof and the ridge vent is covered, ventilation goes to zero. Even with the best insulated attic there will be heat loss and possibly radiant heating due to the sun (on my south facing roof) that will heat the attic area enough to melt the snow on the roof. So ice dams will occur unless you remove the snow covering the ridge vent. I just have never read anything mentioned about making sure it is clear, which requires getting up on the roof to do so.

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  11. Roofing Wizard Post author

    Hello Greg,

    Yes, having a low slope roof can be a great challenge, I personally believe that one should never install roofing shingles on any roof that has a pitch of less than 4 to 12. I think you will benefit by reading an ice dam prevention guide for lower slopped roofs.

    Alex

  12. Russ Eaton

    Hello,
    I had a standing seam metal roof installed in 2001, It has always had ice backup’s along the eve’s. Witch in turn has lead to leaks , The company that installed the new metal roofing has been back two times. The roof still leaks, The thing is this there is not much of a ice dam due to most of it has slid down the roof only to stop before it fall’s normally hanging out from roof two feet or so. Now this leak begins at the ice build up on the main roof and leaks down into the kitchen. I feel some how it is running behind my aluminum siding and trim ? I can locate it in the kitchen , and to me my eves seem to be frozen , I can see water dripping from them when thawing from behind the aluminum trim.
    Help please
    Russ

  13. Russ Eaton

    Hello,

    Today the installer shows up to take a look, Little did i know the original owner had sold out. The guy that purchased this roofing business, Said he would have to wait until spring to fix the problem witch I totally understand. His solution to the problem is to unlock each panel and apply sealer to the seams ? I expected to be asked about my attic insulation and ventilation, But was not . Should the house and the eves have been flashed ? I have seen this on different installation procedures. Now I have no way to improve my attic insulation / ventilation so that is not a option. Also this roof being 12 years old when it was new the snow did slide off it ……. What does it need a wax job :) But for real is unlocking the seams a good idea ?

  14. dan garnic

    g just bought 4 pitch asphalt shingle roof home, 9 years old and roof replaced 3 years ago. cathedral ceilings no attic and no crawl space. plenty of ventilation i think, lot of soffett holes and peak vent. insulation about 5 inches of fiberglass. so lot of heat penetration. leaks from ice dams continue. choices? pull off all the roof and spray foam, then reroof, with a cold roof 8 inches high. or put 2 inch foam panels between 2×4 on top of the current roof, add r10 then roof on top? will a metal roof alone resolve? metal on top of 1×3 will add some ventilation under the metal, but will it buckle? so many ideas, but what is the solution? thx d

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