In cold regions, icicles and ice dams may develop on roofs that slope to cold eaves. Ventilating the space below the snow-covered roof with outdoor aur to create a "cold" ventilated roof is often an effective way to avoid such problems. Several buildings in northern New York were instrumented to determine how the attic temperature influenced icing. We observed that problematic icings developed very slowly, if at all, when the outside temperature was above 22F. Such icings can be avoided by sizing natural, and if necessary, mechanical attic ventilation systems to maintain an attic temperature of 30F when the outside temperature is 22F.