Ventilation in an attic occurs because of wind or temperature differences. If you only have vents on top of your roof, when they are covered up by snow, ventilation can't occur. With soffit/eave and gable-end vents, some ventilation may occur, but because of the low moisture-holding capacity of cold air, the ability of the inlet air to remove moisture that enters the attic from the living space will be limited. The formation of icicles at the edge of your roof is more related to warm indoor air and heat escaping to the attic than with lack of attic ventilation. More insulation in the ceiling, combined with an effective air barrier, reduces the chance of icicles and moisture problems in the attic. An air barrier minimizes moisture movement into the attic space, and insulation further reduces heat loss into the attic.

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