Ice Dam Prevention Guide

Insulation, Ventilation & Ice & Water Shield

Ice dams form when warm attic air melts roof snow at the ridge and the meltwater refreezes at the cold eave. The fix is a three-part system: adequate attic insulation (R-49 to R-60 in cold zones) to keep heat out of the attic, balanced ridge-and-soffit ventilation (1:300 NFA ratio) to keep the deck cold, and ice & water shield extending 24 inches past the interior wall line at every eave. This guide explains each layer and links to the matching calculators.