Winter conditions bring a different type of problem. During the cold months of the year, the air inside the home is warmer and carries more water vapor than the colder, dryer air in the attic. Cooking, laundry, showers, humidifiers and other activities using water contribute to this condition. There is a strong natural force, termed “vapor pressure”, that causes water vapor to migrate from high-humidity air or materials to low-humidity air. This migration of water vapor passes through ceilings, insulation and wood and even successfully circumvents a vapor barrier. It moves into the attic space where it can readily condense into liquid water on the cooler structural members-rafters, trusses, and especially the cold roof sheathing. Condensation moisture within an attic or ceiling space can dampen and compress insulation. Even small amounts of condensation can have a substantial effect in reducing the “R” value of the insulation, thus creating faster heat loss into the attic space. This will eventually lead to mold, mildew, rot, ice damming, etc…