Ask Todd Miller *Metal Roofing Expert

Snow, Ice Dams, and Metal Roofing

February 3, 2011 | Filed under: Misc

I was looking recently at my website statistics and one thing popped up clearly – folks are really searching for information on roof ice dams and also metal roofing as a possible solution to ice damming. This has been a tough winter with snow and ice in areas of the country that do not normally get snow and ice. This poses a unique problem because, while there are ways to help make a home be resistant to ice damming, if you do not normally get much ice and snow, you don’t build your home to handle it well. Of course, oftentimes weather patterns repeat themselves for a few years so the folks getting ice and snow this year can quite possibly expect it in future years as well.
So, let’s take a look at ice damming on roofs …

There are two primary reasons why ice damming occurs on roofs. They are as follows:

1)Heat from inside the house escapes into the attic and then reaches the roof, causing “hot spots” that melt the snow. This melted snow then runs down the roof until it hits cold areas of the roof at the eave overhangs where it re-freezes. This leads to a gradual build-up of ice on the bottom edges of the roof. This situation is most prevalent when outside temperatures stay cold and there is no sun to cause melting over the entire roof rather than just the aforementioned “hot spots”. This phenomenon, of course, describes winter in many areas.

2)Converging snowloads on the roof, often at valleys in the roof, cause “packing” where the snow cannot slide off the roof. Eventually as this snow packs tighter and tighter, ice is formed.

When analyzing a problem, I always like to first look at what can be done to permanently fix the situation rather than just try to relieve the symptoms. So, in the two above scenarios, what is a permanent fix? Read on!

1)Eliminating “hot spots” on a roof which lead to ice dams is best done by increasing insulation on the attic floor and also increasing ventilation in the attic. Insulation helps hold heat inside the home where you want it. Ventilation helps keep the attic as cold as possible. To avoid ice dams, ideally, you’d like your attic to be the same temperature as outside. The key to ventilation is having good intake vents and also good exhaust vents. Intake and exhaust vents need to be well balanced in terms of the air that can flow through them. They also should be positioned in a way which continually “bathes” the entire underside of the roof deck with fresh cold air from outside, eliminating “hot spots”.

The issue with all of this is that some homes really are not constructed well for ventilation. That is when building a roof over the existing roof, creating a new vented chamber, can be very wise. This is also called a “cold roof”. It is not a cheap or easy fix but it is a very good, permanent fix. A product like Green American Home’s ThermaDeck can help make this method be even more effective by combining ventilation with insulation and reflectivity.

A true bonus of increasing home insulation and ventilation is that these things also help reduce air conditioning loads in the summer. So, particularly for homeowners in temperate climates, these solutions to ice dams can help reduce summer energy costs as well.

2)If ice dams are being caused by roof geometry (“shape” or “footprint”) and the resulting converging snow masses, it is difficult to arrive at a permanent fix shy of major changes to the home’s design. In this case, adding things like snowguards on the roof, uphill a bit from the trouble areas, can help hold snow and prevent it from sliding so quickly. If you can hold the snowload until it melts naturally, then you can avoid the converging snowloads and the resulting ice dams.

The next question then becomes, what if these permanent fixes cannot be made or, in the case of roof shape, do not have adequate effect? In that case, there are systems which can be added to your roof that will help in melting unavoidable ice dams. Some of these systems lay on top of the roof, such as “heat tape” and are easily added to any existing roof. Other systems become more permanent and integral to the structure and actually are placed under the roof system or under the roof deck in the areas where ice dams occur, heating the roof surface and preventing the ice creation and accumulation.

The next question that folks ask a lot of times is whether metal roofing avoids ice dams. Companies like Classic Metal Roofing Systems and Kassel & Irons produce attractive residential metal roofing systems and sometimes make the claim that their systems can help minimize ice dams. The fact is, metal roofing can help but it is by no means a cure-all for ice dams.

Metal roofs tend to shed snow more quickly than most other roofing materials. This is because they have a fairly smooth top surface and also because, when the sun does appear on winter days, heat from the sun passes through the snowload, hits the metal, and is reflected back outside. It then starts to melt the bottom of the snow on the roof over the entire roof not just over the heated areas. Once that snow melts a bit, it gets slippery and tends to slide off the roof, much like snow off of the hood of your car once the engine warms up.

However, metal roofing does not necessarily help prevent ice dams from converging snow and, if the sun doesn’t come out, snow can hang around on metal roofing for a long time just as it does on other roofing materials. So, that brings us back to not wanting to ignore the possibility of permanent solutions to ice damming even on homes where metal roofing is being installed. One benefit of metal roofing, if ice dams do occur, is that typically due to the interlocking nature of the panels, the strength of the metal, and the underlayments used beneath the metal panels, there is less chance of the melted snow and ice working their way into the homes, its walls, or its overhangs, than there can be with other roofing materials. So, even though ice dams may occur, they will be less damaging.

If you have a particularly stubborn ice dam situation, feel free to email me at todd@asktoddmiller.com. Send me pictures or roof diagrams if you can including details on your home’s construction and ventilation, and I will do my best to offer solid solutions.

20 Responses to “Snow, Ice Dams, and Metal Roofing”

  1. [...] Asktoddmiller.com has recently published a great article on Snow, Ice Dams, and Metal Roofing. [...]

  2. Philbrick says:

    Thank you for identifying the existence of the “ThermaDeci” product in the mix.

  3. Angela Rice says:

    I have the classic metal roof and love it, however in the back corner (no sun) there is quite a large ice dam. And being Feb. in Maine I have 6 more weeks of cold. I don’t want to damage the roof but how do I get the ice off?

  4. Les Deal says:

    You mention the ease of installing heat tapes. How do you easily install heat tapes on an Oxford aluminum roof? I have a situation where I need to come up with a way to secure the tape without putting holes in the roof. I also want to prevent the tape from being ripped off when the snow slides off. Maybe I have to resolve to using snow stops to stop the snow from sliding.

  5. Denise says:

    Hi Todd, I wanted to ask a question about flat rubber roofing. We recently 10-7-2010 had a new rubber roof put on ( by a guy named Todd Miller, no you tho). Last week, We had a huge leak in the back room, creation a hole about 6 inches wide also leaking down the walls. I called our guy to come out ASAP to fix it. He said this was normal and patched it up with muck and said he would return in a few days to fix the hole. We havent heard from him since. I cannot believe a new roof would leak this bad. Was his repair enough? Is he responsible to fix the hole? I think this guy is a big con man and we got ripped off. BIG TIME. Thanks Todd.

  6. toddmiller says:

    Thanks Denise,

    It’s really hard to say. It is not unusual to have a callback on a rubber roof. It sounds like perhaps a seam or a seal around a protrusion opened up.

    I would certainly keep a close eye on things and if you continue to have concerns, consider consulting with the manufacturer of the roof or having another quality contractor come do an inspection and opinion.

    Good luck.

    Todd

  7. toddmiller says:

    Thanks Angela. Good to hear from you. It has been a miserable winter for ice damming. And certainly lack of sun can be a factor. You may want to consider seeing if there is anything that can be done from a ventilation standpoint next summer. One thing to keep in mind is that sometimes with a metal roof, ice dams will just eventually melt / evaporate and no damage is done. You can use limited salt if you must … just do not do it on a regular basis and rince the roof as soon as practical afterward. If you wish, send me a picture of the ice dam todd@asktoddmiller.com and I will see if I have any other ideas. All Best.

  8. toddmiller says:

    Thanks Les. Well, you got me. :-) haha Heat tapes are easier to install on some products that others. I guess about the only choice is rivets or sheet metal screws and then seal over them well with quality sealant or the little covers that I think the heat tape manufacturers sometimes provide. Have you tried anything else? And if the roof is real large or steep, it may take snowguards uphill of the heat tape as well. Wow. Have I helped at all? Thanks again!

  9. Ry Hoopes says:

    Todd have you ever used SnoShield snowguards? http://www.roofthings.com/category/2/snow-guards.aspx

    I’m looking at getting some and want your opinion.

  10. toddmiller says:

    Ry,

    I have had no personal experience with them. However, provided they are sized to fit over your panel ribs, they should do well (assuming you’re looking at the ones that fit over the ribs).

  11. RICK COOL says:

    HI TODD WE SPOKE ON THE PHONE A COUPLE WEEKS AGO I HAVE THE RED RUSTIC ROOF THE ONE LEAKING ON MY BACK WALL DONT KNOW IF INTRGRITY EVER SENT THE PICS BUT IT STILL LEAKS
    I BOUGHT HEAT TAPE BY FROST KING AND THERE IS NO GOOD WAY TO HOOK THEM ON FROST KING DOSNT RECOMMEND THEM FOR METAL ROOFS I HAVE EVEN TRIED PUTTING ROCK SALT IN THE GUTTERS
    THE FUNNY THING IS IT DIDNT LEAK ON THE WALL WHEN I HAD A SHINGLED ROOF ITS A VERY PRETTY ROOF BUT IT NOT DOING WHAT THE AD SAYS DRILLING HOLES DOSNT SEEM LIKE A GOOD IDEA SOONER OR LATER IT WILL LEAK CLASSIC MUST HAVE SOME KIND OF CLIP OR SHOULD MAKE ONE IM NOT SURE WHAT TO DO WOULD ENJOY A CALL THANKS R COOL

  12. toddmiller says:

    Thanks Rick. I am sorry about the ongoing problems. I suspected it was ice dam related when we talked but I wanted the photos to try to confirm that. We contacted the contractor right away and have been promised photos … but still no photos. Do you have any way to take pictures of the affected area from the outside — just from the ground — and email them to me at todd@asktoddmiller.com? As far as heat tape … there really is no way to do it other than use the clips that come with the tape … attach them with rivets or sheet metal screws and then seal over them real well with a quality sealant. Really, before we go that route though I’d like to know / see (hoping for the photos) whether there is a way to increase ventilation. This has been a horrible winter for ice damming. I have lived in the same house for 16 years — 14 with with metal roof — and you guessed it, for the first time ever we have had some ice dam issues this year, albeit in a crazy dead valley area of the roof with no ventilation.

  13. Brian says:

    Todd, I appreciate your assistance and efforts here, but I have to disagree on a couple of your points. “Heat from the sun passes through the snowload, hits the metal, and is reflected back outside.” ‘Heat’ passing through snow? There is lots of documentation that solar radiance melts the top surface of the snow which drains through the roof, but there is no heat traveling through snow and returning to the ‘outside’.

    Your reason #1 for ice dam formations is spot on, but #2, ice formations in valleys, I believe is caused by #1. If the simple convergence of ice and snow in a valley caused ice, ice would be as common above the plate line (over the interior) as it is over the exterior. Valleys are indeed a serious problem, but predominately because the overhang is longer along the valley line, and the valley is a cluster of flashings, membranes, and roofing. Unlike and ‘open field’ of roofing, valleys have many ways to fail. Do you have any authorities supporting these points? Maybe I know nothing. Thoughts? Thanks.

  14. toddmiller says:

    Thanks Brian, I really appreciate your comments and taking the time to read my post. You bring up some great points. It sure sound slike you have a lot more experience with this subject than I do and on points where I need to correct myself, I want to do that.

    I see that you’re form an area where you have a great deal of first-hand experience with snow and ice! It’s hard to argue with that.

    My observation has been that, when the sun comes out and there is a snowload on a metal roof, as long as the temperatures are not absolutely frigid and provided the sun stays out for a few hours, the snow will at least begin to slide off the roof and when it does this it can be observed to be very slippery on the bottom side of the snowload. This happens over the entire roof, not just the heated areas, causing me to believe it was due to reflected radiant heat from the sun. However, I bet you’re right. I suspect it is from the snow starting to melt from the topside. I never thought of it that way before but it makes sense.

    My observation of converging snow at valleys has also been anecdotal. I have seen it start to create ice as it does that in valleys but exactly why or how, I am not sure. My point was just that valleys can be a contributing factor. I maybe made too big of a deal about that in the article.

    I hope this helps to clarify some for our readers here. I did not mean to mislead and I really appreciate your information. Like I said, I am sure you know this subject far too well.

    Great to make your acquaintance. Thanks again and feel free to weigh in here anytime … in fact if you’d ever like to be a guest author on here, just send something my way and we will get it up for you!

    All Best!

  15. Clarence says:

    I live in Anchorage, Ak and get ice dams on the edge of my garage. It’s a safety hazard as well as damaging as it tears off my gutter. What product can I use to keep the ice from forming?

  16. toddmiller says:

    Clarence, as you probably know, ventilation is often a key to avoiding ice dams but there are always situations where even it is not enough. There are a variety of snow and ice melt products and systems available. The one we like best is Sol-Ice. http://www.sol-ice.com We actually distribute this product and, if you send us a sketch of your home and garage with dimensions and orientation, we will work with the folks at Sol-Ice to give you a proposal.

  17. Clarence, I am sure we can help you out with this problem. I am the CEO of Sol-Ice and as Todd Miller said we are working together to solve problems just like yours. If you have any Pictures of the problems you could send them to AskUs@sol-ice.com. We also have a form you can fill out that will give us most of the information we need to get you pointed in the right direction this shortened URL should get you there. http://ow.ly/eJ68u

    Thanks Todd for the mention!

  18. Fred says:

    Todd

    I recently had a steel roof installed over my deck. The deck has a shallow pitch. While we seldom have heavy snows I was wondering if installing a heat tape/wire under the metal panels would melt any snow build up?

  19. toddmiller says:

    Thanks for visiting my site, and for your question.

    If you can raise the temperature of the steel to over freezing, yes, it will help avoid snow build up. And, yes, you can do that heating from the bottom side.

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About Todd

Todd's expertise comes from his years of experience in metal roofing manufacturing. As president of Classic Products, Inc. based in Piqua Ohio, Todd runs two of the world's leading manufacturers of residential metal roofing. His personal goal is to educate homeowners of the long-life benefits of metal roofing.

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