Ice dams in Merrimack form when warm air from the living space heats the roof deck above the freezing point, melting snow that then refreezes at the cold eave overhang. The pooling water backs up under shingles and causes interior leaks. Master Roofers addresses ice dams at the root cause: improving attic insulation and ventilation to keep the deck cold uniformly. We also install extended ice-and-water shield membrane at eave edges as a secondary defense.