The issue of attic ventilation and the amount of ventilation necessary is controversial. Based on research conducted to date, the strongest case for ventilating asphalt shingle roof assemblies with outside air exists for residences located in cold climates and where snow accumulations persist on roofs for extended periods of time. Under those sets of conditions, ventilation has been shown to be a valuable strategy for removing excess moisture from attics, thus preventing condensation that can damage roof sheathing and preventing ice dam formation.
It has also been shown ventilation with outside air reduces average attic air temperatures in summer. Research has not verified a significant effect of attic ventilation on the average roof surface temperature. In fact, research results indicate ventilation has less effect on average roof surface temperature than the facing direction of a roof surface or roofing material color.
Some sources available to homeowners suggest attic ventilation is necessary with asphalt shingle roof systems. Asphalt shingle manufacturers’ warranties, for example, may make coverage conditional on meeting their minimum ventilation requirements. Homeowners should consult manufacturers for specific ventilation requirements when selecting an asphalt shingle product.
Ventilation of attic spaces can be accommodated by using one of two methods:
Further discussion about asphalt shingle roof assembly ventilation is organized around the following topics: