Attic ventilation for asphalt shingle roof assemblies
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: