Heat cables help, but they don't fix the root cause. They melt channels along the eave so water can drain instead of pooling behind an ice ridge — useful, but they don't stop the heat loss that creates the dam in the first place.
Where heat cables earn their keep is on the spots insulation alone can't solve: valleys, roof-to-wall transitions, and around dormers. We usually recommend them as one part of a fix — heat cables on the problem areas, plus attic insulation to R-49 and balanced ventilation to keep the rest of the roof deck cold. Cables alone on an under-insulated roof just run up your electric bill.
A quick primer on how they work. Heat cables — also called heat tape — run in a zigzag along the eave and down through the gutters and downspouts, warming just enough to hold a drain path open so meltwater can escape. Self-regulating cables are worth the extra cost over cheap constant-wattage ones: they dial their output up and down with the temperature, so they use less power and last longer. Most draw roughly 5 to 8 watts per foot, which adds a modest but real amount to your winter electric bill.
Cables are a targeted tool, not a whole-roof cure. They usually last around 5 to 10 years, they only protect the exact path they cover, and on an under-insulated roof they just melt one channel while the rest of the dam keeps building. The setup that works is cables on the trouble spots — valleys, dormers, and roof-to-wall joints — backed by attic insulation to R-49 and balanced ventilation that keeps the rest of the deck cold. That combination is what actually stops the dam.