The most common justification given for venting attics is to prevent ice formation during the winter. A research review by Anton Ten Wolde and William Rose concluded that while ventilation plays some role in keeping attics dry controlling indoor humidity is much more important. Another justification for attic ventilation is to keep attics cool and prevent ice dams. It appears that ventilation makes little difference in ice dams formation unless large amounts of heat are escaping into the attic from below.
Good insulation is much more effective in keeping the attic cool.
The third reason for ventilation is to extend shingle life by keeping roofs cool during warm weather. In reality the temperature of the sheathing directly beneath the shingles was only 10 degrees Fahrenheit lower for insulated attics than it was for the sheathing above unventilated attics. Sunlight and wind were the primary predictors of shingle temperature. You are the 3645th access to this page.