February 8, 2010 | Filed under: Ice Dams and Metal Roofing, Roofing Help Podcasts
Folks who live in northern climates that are prone to snow and ice know that one of the things that they hate seeing happen on the roof is what we call ice damming. Ice damming can be very dangerous it can lead to leave to leaks, It can lead to roof damages. So how do you make sure that you’re going to avoid it?
What are Ice Dams?
Ice damming actually occurs because heat from inside your home migrates up into the attic. Once that heat migrates into the attic if it’s not vented out properly, it creates hot spots on the roof. So that means that your shingles, or metal roof, or whatever covering is on your roof gets hot in certain areas. When it gets hot, it’s going to cause the snow load on your roof to melt. When that snow load starts to melt it causes water to start flowing down your roof. Now think about this… that water flows down your roof until it hits the bottom of roof (which is not over the living space…that is actually over the overhang on your roof) and that’s where it starts to ice. Once it starts to ice on the overhangs of your roof, it just starts to build up and you can actually build up ice several inches or even a foot or more thick on the overhangs of a house. As that happens that water just starts to back uphill, and it can’t escape the roof anymore. It runs into this ice dam, starts to backup, and that’s where it gets underneath shingles, gets in your house, and causes problems.
How Do I Avoid Ice Damming
So, what’s the best way to avoid ice damming? Keep your attic cold. The best way to do that is through ventilation. If you got proper ventilation (meaning you’ve got air coming in at the bottom of roof) and then flowing properly through the Attic to exhaust out of the top then you’re going to keep your attic cold… you will not have those hot spots develop on the roof, and as a result you will not have ice damming. Don’t care what type of roof you have installed on your house whether its conventional shingles, whether it’s metal, whether it’s wood shake, ice damming can be very damaging and dangerous and you don’t want it to happen.
So, good ventilation is the number one key to avoiding ice dams on your roof.
Todd Miller has spent his entire career in the metal building products manufacturing industry. He is president of Isaiah Industries, an organization recognized as one of the world’s leading metal roofing manufacturers. Todd is currently Vice President of the MRA (Metal Roofing Association) and a Past Chair of MCA (Metal Construction Association). Through his website, he strives to raise the bar on standards and practices to provide property owners with the best possible products for successful roofing projects.
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To prevent ice damming, as a home inspector, my advice to my clients takes a different perspective than yours. My primary objective is to first keep heat out of the attic. Most of the
heat entering the attic in the winter is from air infiltration from the house through gaps between the ceiling and the attic. Plumbing and electrical chases, drilled holes, gaps around chimneys, and plain old gaps and spaces all add to heat exiting the house, from where you want to retain the heat, to leaking into the attic where you don’t want the heat. Attic ventilation has some importance, but that is treating the symptom and not the cause. Plus attic ventilation increases the draw of the heated air into the attic, further increasing ones heating bills. Sealing the basement also goes a long way towards preventing convective air loops drawing heat from the heated area into the attic.
Also important is to make sure that all fans that vent into the attic terminate completely outside the attic, not into the attic nor vent only closely to roof vent.
Next is the mechanical system. A furnace in the attic is asking for problem and is inappropriate design for a home in a cold climate. If there is duct work in the attic, it is crucial that it be properly sealed BEFORE insulating the duct work. That means using a mastic at EVERY joint, or proper metalized duct tape. Typical duct tape is not appropriate to use on ducts, especially not in an attic, where the summer temps up there are too high for the standard duct tape to last. Having proper attic venting, with at least half the vents in the bottom edge of the roof is the icing on the cake.
Hope this is helpful
RJ Frank Home Inspections/A Buyer’s Ally
Ann Arbor, Michigan 48103
Thanks, Mr. Frank. Great input. I do agree with everything you’re saying. I was not aware that most heat transfer into the attic was from gaps and cracks … that is very interesting. Certainly your ideas are all great places to start! Thanks!