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It is our first winter in a new-to-us house, that has a pretty flat roof (3/12-to-4/12 pitch), and a ridge vent along the entire top of the roof. We just had the snowiest December on record (Minnesota), which put a good 36" of snow on the roof, burying the ridge vent. I have been up on the roof, and have cleared most of the snow, but we have a good 4' ice-dam that has bridged to/filled the gutters (and is a good 4" over the top of the gutters currently). My primary concern, is that water seems to be getting behind the facia, into the eaves, then coming out on the outside of the house, and running down the exterior siding where it freezes. So far there is no apparent water damage inside, but I want to get this cleared up ASAP before it gets into the house.

My questions are-

1) What is the best way to get rid of the ice dam (the entire edge of the roof, on both sides of the house, 55' on each side, has an ice dam going 4-6' up the roof)? I have thrown a bunch of potassium chloride up on the roof, but it didn't seem to do too much. I'll try the nylon tube mentioned in the answer here, but how should I orient it to get the most ice off the roof?

2) How do I prevent this in the future? I have a roof rake, and can rake the first 6-8' of the roof, but does that do any good if the ridge vent is blocked? It sounds like the heat tape doesn't work all that well. Thoughts?

Edit- Well, the nylon stockings with potassium chloride have been on the roof for 8 hours now, and they have yet to melt anything... hummm...

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While we're at it: in snowy country, build a steeper roof. Also, insulate your ceiling well, so the snow won't melt-and-freeze to make the ice dam. Or make a living roof, nearly flat, very strong, keep the snow as insulation. –  Jay Bazuzi Dec 27 '10 at 19:56
    
Thus why every other house in this state has a steep roof ;). Unfortunately, my house was built a decade before I was born, and thus I had no say in the roof pitch. :D –  MarkD Dec 28 '10 at 3:02
    
Have faith mark, I have used the pantie hose technique dozens of times and it never failed yet. If it is not working fast, I have to assume the ambient temp is very cold right now. Chlorides work best in temps above 20 degrees. It should kick in as soon as it gets some sun on it. You can also make a starter valley with a hatchet or hammer claw,(be careful not to damage shingles) then lay some chloride directly on the ice, then lay your sock full of chloride on that. Kind of like jump starting the process. –  shirlock homes Dec 28 '10 at 9:49
    
should have mentioned, you can also pour some warm water on your socks to help get some of the chloride flowing and in contact with the ice. –  shirlock homes Dec 28 '10 at 12:57
    
Thanks for restoring my faith, and those tips. You're right, it is quite cold (9 deg outside right now). Luckily, the weather people are saying we're going to have a heat wave over the next 3 days, with temps soaring into the mid-30s. Hopefully I can take advantage of the high temps to fix this ice dam, and use the tips in your great answer below to minimize this in the future. –  MarkD Dec 28 '10 at 15:00

3 Answers 3

up vote 9 down vote accepted

Ok gentilmen , lets talk ice dams. First and foremost, what causes an ice dam to form anyway. Heat trapped in an attic, either from heat loss from the house or sun beating on the roof, cannot escape quickly and melts snow on the roof. This water drains to the bottom of the roof where it runs across a cold edge and freezes. The overhang of your roof (soffit area) is typically not over a heated area and tends to be very cold, much colder that the rest of the roof. Even with a well insulated ceiling and good ventilation ice dams will form if conditions are right. This is where the old saying,"an ounce of prevention is worth a pound of cure" rings true. Any time you have a heavy snow load on your roof followed by some moderate temps or sunny days, some natural melting is going to occur, especially if the ridge vents are buried in snow. Sun hitting the gable ends will heat up the attic a bit too. Many times the ice dam starts in the gutters then bridges over to the roof edge and starts it's way up. Once it starts, there is now way to stop it unless the source of water building it is taken away. The only way to deprive the ice dam of more water is to REMOVE THE SNOW FROM THE ROOF AND MAKE AN EXIT FOR ANY REMAINING WATER TO DRAIN. This is why it is so important to use a roof rake soon after a snowfall to remove several feet of snow from the edge of the roof. With the snow removed, you can see if a dam is starting and can address it quickly while it is small and easy to treat. Other things to consider may include, if you live in an area where your ridge vent commonly is covered in snow, add a gable end vent on both sides of the house and be sure the soffit vents are equipped with "proper vent panels" inside and that they are not blocked by insulation. Always use a minimum of 6 feet of Grace ice and water shield, or if you want a good insurance policy against leaks, cover the entire roof with Grace before shingling. This may cost a bit more up front, but pays for itself in the long run. Maximize your attic insulation. Take a good look at your gutters and consider lowering them if they are too close to the drip edge where ice dams begin. There is no one thing that will prevent ice dams, but if you look at all the preventions at your disposal, dealing with them will be a lot easier. Sorry for preaching guys, but I give this same speel to many customers every year when water is leaking in their homes and they are shelling out big bucks for repairs. Two years ago here in Maine, the huge snowfalls and subsiquint ice dam problems prompted homeowners insurance companies to send out letters telling policy holders that they would not cover a second loss if these precautions were not met.

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The problem I had with raking the roof, was the ice dams reformed but now they were further up the roof where I couldn't reach them. For my house, since I can't clear the entire roof, I'm better off trying to deal with ice dams at the drip edge where I can reach them and where my ice/water shield is providing protection. –  ChrisP Dec 28 '10 at 12:40

It seems there are many downplaying the positive impact heat tape has to prevent ice dams especially in the shaded valleys. We are in the Rocky Mountains in Colorado at 7K' and average 250" of snowfall/year. Several years ago, we had a valley with 10' of snow and an ice dam at the bottom that did the classic melt and leaked above the ceiling and then into the home. I tried ice melt type solutions, but this didn't work especially when we weren't home. We had heat tape professionally installed and never looked back. It doesn't completely remove the ice and snow unless we would have installed an exce$$ive amount. However, the classic ice dam is gone and the snow has never been over 1' even with last year's record snowfall. We do have the tape running along gutters and in the downspout. It works, it is easy, and 500' only increased our electric bill by $100-$150/mo from Dec-March. I only turned off the areas that had major sun exposure and were dry at times. Otherwise, we left it on 24x7. The cost was minimal compared to the potential home damage. After 3 years of success, I thought that I would share that if done properly, then professionally installed heat tape works and gives you peace of mind.

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I had bad ice dams after last years blizzard in DC. My roofer told me to just break up the dams taking care not to damage the underlying asphalt shingles. I ended up using a large rubber mallet. It probably wasn't the best approach but I figured the cost of repairing some shingles would be better than repairing any water damage inside the ceiling/walls of my house due to the ice dams.

I also temporarily changed the insulation in my attic to allow some warm air into the areas that were freezing. Since heat rises, the peak of a roof can be expected to be warmer than the lower part. So I figured it would help to make sure the lower part was getting enough warm air, even it that meant some loss of energy. Again the trade off being what is cheaper, losing some heat to thaw the ice dam or dealing with the resulting water damage in the house?

My house was due for new shingles so I had the roofers apply several feet (don't remember the exact amount) of an ice and water shield - basically a rubber sheet that sticks right to the lumber under the shingles. So any water that gets under the shingles will hit this rubber sheet and flow under the shingles to the drip edge without leaking into the house.

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I don't live in Minnesota, but I would bet an ice/water shield is required by code up there. If I had an old roof I would probably try breaking up the ice by hand, but if I had a new on I don't think I would want to risk damaging the shingles. –  auujay Dec 27 '10 at 22:56
    
That is the thing... we have a new roof, and ice/water shield going back a good 4' from the edge of the roof. My bigger concern is that I have frozen water on the siding of the house.. so somehow the water is creeping under the eaves, and down the siding... and it appears that the water is coming from behind the fascia on the eaves. –  MarkD Dec 28 '10 at 3:00
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Chris, hope I don't offend you, but removing insulation to warm the peak of the roof is exactly the wrong thing to do. The melted snow from the top will get caught behind the ice dam on the bottom edge and cause more problems. If you don't remove the dam, any melt is gonna back up under your shingles. Also, standard practice now is to install a minimum of 6 feet of ice and water shield. –  shirlock homes Dec 28 '10 at 9:39
    
@Shirlock - No offense, I probably wasn't clear enough. I removed insulation from the bottom, not the peak. As I stated, warm air rises and thaws from the top first, so I had to get warm air to the bottom so the thawed water wouldn't refreeze. –  ChrisP Dec 28 '10 at 12:28
    
I should add that my roof line ends just a few inches past the wall. I don't have an overhang like you find in most home construction. –  ChrisP Dec 28 '10 at 12:36

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