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…
Best Answer
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.