A properly ventilated attic increases comfort and saves energy costs all year long. During the summer, excess heat builds up in the attic during the day and results in higher energy costs for cooling. During the winter, moisture produced within the home may move into the attic if ceiling vapor barriers are not installed properly. The moisture will condense and cause insulation and construction materials to deteriorate.
Attic ventilation can be accomplished by gravity ventilators, wind assisted ventilators or power ventilator. Regardless of the method used, the purpose is to provide uniform ventilation of the attic for proper temperature and moisture control.
In cold climates like Minnesota, the primary purpose of attic or roof ventilation is to maintain a cold roof temperature to control ice dams created by melting snow, and to vent moisture that moves from conditioned space to the attic. Melted snow, in this case, is caused by heat loss. The heat loss is typically a combination of air leakage and conductive losses. The air leakage is due to infiltration from the conditioned space and from leaky supply duct work and from penetrations of the ceiling lid. The conductive losses are usually from supply duct work and equipment located in attic spaces above ceiling insulation. Conductive losses also occur directly through insulation, or where insulation is missing or thin.
The following diagram illustrates how the flow of air happens in your attic.
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