Ice Dam Video
What has happened is this. If you look under the roof ice dam, you will see the soffit and the exterior of the house. Well, guess what's happening? Right behind the ice dam where you can see the shingles. There is enough heat that can pass through the insulation and radiates to the underside of the roof deck. This heat melts the snow pack.
As soon as the melted snow flows down the roof and touches the ice-cold gutter, it starts to freeze instantly. As this process continues, the ice damming gets thicker and thicker.
On another area of the roof, there are no ice dams. So why is there no ice here? What is different? This roof is over the garage and there is no heat in the garage. Thus, no heat comes up and heats the underside of the roof. Melting the snow pack and causing it to freeze when it hits the cold edge of the roof.
If you want to prevent ice dams, there are a couple of choices. First thing is to get the snow off the roof. Don't beat the roof chopping ice, remove the snow pack with a snow rake.
Another one of the ice dam solutions is putting a radiant barrier on top of the insulation, making sure it doesn't touch the insulation. This barrier would run up the underside of the roof leaving an air gap of about 1-1/2 inches on top of the radiant barrier. This barrier would cause all that escaping heat to be deflected back down into the house.
If you want to stop the ice dam leaks, you will need to put an ice and water shield on the roof. (Click here to watch my Ice and Water Shield video.) This ice dam membrane will prevent the water backing up behind the ice dam from getting into the house as the water gets under the shingles. In heavy snow areas, like New England, the ice and water shield needs to extend up the roof about six feet. Better yet, apply it to the entire roof. This ice dam membrane can only be put on when you are re-roofing or building a new home.