Ice Dams can be a fact of life, or are they?
With the return of winter,
As the ice keeps building in height, water accumulates behind the dam above the heated attic space. When the dam water is high enough, the water level rises and works it way under the shingles to find an entry way under the shingles, barrier, and sheathing then into your home.
Generally speaking, if an attic space is unconditioned, has no purposely manufactured heat, it should be as relative in temperature and humidity as the outdoors. The likelihood of icicles and ice damming would be greatly diminished.
Need help defining your attic venting?
Read this Handyman article. http://www.familyhandyman.com/roof/prevent-ice-dams/view-all