Ice Dams Do's and Don'ts
Self-sticking rubberized sheets can go under roof shingles wherever water could pond against an ice dam: above the eaves, around chimneys, in valleys, around skylights, and around vent stacks. If water leaks through the roof covering, the waterproof underlayment provides a second line of defense.
Sheet-metal ice belts can help, if a shiny 2-ft-wide metal strip along the edge of the roof is acceptable. Ice or snow belts are used for some patch-and-fix jobs on existing houses. The flashing, installed at the eaves, imitates metal roofing by shedding snow and ice before it causes a problem. It works-sometimes. The problem with ice belts is that a secondary ice dam often develops on the roof just above the top edge of the metal strip.
Placing electric heat tape in a zigzag arrangement on the shingles above the edge of the roof is a poor solution. I have never seen electrically heated cable actually fix an ice dam problem. The considerable amount of electricity it takes to prevent ice formation is expensive, and the heating must be done in anticipation of ice dam conditions, not afterwards. Over time, heat tape embrittles shingles, creating a fire risk. It's expensive to install, too, and water can leak through the cable fasteners. Often the cables create ice dams just above them. Don't waste time or money on this retrofit.The worst of all solutions is shoveling snow and chipping ice from the edge of a roof. People attack mounds of snow and roof ice with hammers, shovels, ice picks, homemade snow rakes, crowbars, and chain saws! The theory is obvious. No snow or ice, no leaking water. Unfortunately, this method threatens life, limb, and roof.