Article #127 - Best Practice for Attic Ventilation

Most building codes require roof vents to expel moisture that could cause insulation or other building materials to deteriorate during winter. In summer, ventilation may reduce roof temperatures, thus lengthening the roof life.

Attic eaves.

However, researchers are investigating whether attic ventilation is beneficial for all climates. For years, researchers have believed the cooling benefits of ventilating a well-insulated attic are negligible. Some experts also question whether ventilation effectively removes moisture. Until the research results are available and accepted, builders should follow local code requirements, which usually dictate attic ventilation.

A combination of continuous ridge vent along the peak of the roof and continuous soffit vents at the eaves provides the most effective ventilation. A rule of thumb is to use 1 sq. ft. of net vent opening for every 150 sq. ft. of insulated ceiling or 1:300 if the insulation has a vapor barrier. Vent area should be divided equally between the ridge and soffits.

Cap vents and gable vents can supplement a roof design that has insufficient ridge vent area. Turbine vents can also be used, although they require annual maintenance. Electrically powered roof ventilators are not recommended because they consume more energy than they save. Powered vents can also remove conditioned air from a home through ceiling leaks and bypasses, pull pollutants from the crawlspace into a home, and cause exhaust gases from fireplaces and combustion appliances to enter a home.

This article is an exerpt from the DOE Technology Fact Sheet on Ceilings and Attics: Install Insulation and Provide Ventilation.