Roofing fundamentals
Ice Dams in Colorado, and How to Prevent Them
Ice dams form when warm attic air melts snow on the upper roof, the meltwater refreezes at the cold eave, and a dam of ice backs up the water under the shingles. The fix is rarely more roof. It is almost always insulation, ventilation, and ice and water shield at the eaves.
Three things that actually prevent ice dams
Adequate attic insulation (R-49 plus on the Front Range), balanced soffit-to-ridge ventilation, and ice and water shield extending two feet inside the heated wall line per modern code. Many Colorado jurisdictions also require ice and water shield in valleys, around penetrations, and 36 inches up on roofs at 8 in 12 or steeper.
Why heat cables are not the answer
Heat cables manage symptoms; they do not solve the underlying insulation and ventilation issue. A full system runs $3,500 to $6,000 and adds operating cost. Spending the same money on attic air-sealing, insulation top-up, and ventilation correction during a re-roof is almost always the better investment.