The most obvious reason for attic ventilation is to lower attic space temperature during the warmer months. Attic temperatures can exceed 160°F during hot summer days. Proper attic ventilation can reduce those temperatures by 50°F.  No matter how much insulation is in the attic, heat can still transfer into adjacent living spaces. In fact, extra insulation can actually add to temperature increases because heat is trapped in the insulation. Proper ventilation evacuates this excess heat build-up. As the heat is exhausted the work of the air conditioning system is reduced thereby saving energy and extending the life of the air conditioning system.

Attic ventilation is required in cold environments-it evacuates the warm moist air that heat sources produce. Hot moist air lingering in the attic spaces can condense on the underside of the roof sheathing and rot it out and also causes mold to develop on the interior walls. Cold air in the attic space will not affect the temperature in the adjacent living spaces if properly insulated.

Good ventilation helps prevent ice dams, which begin to form when warm air in the attic melts the snow from beneath and creates runoff that refreezes on the colder eaves.

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