According to Owens Corning, sloped roof systems are installed with ventilation to “address excess heat and moisture that can otherwise wreak havoc on your home.” Improper ventilation systems can also affect the roof covering itself, typically asphalt composition shingles. Various factors should be considered in the selection of ventilation systems including attic size/shape, roof type, roof dimensions including ridge lengths, roof pitch, and intake options. Potential harmful effects on the roof shingles include blisters, premature granule loss, thermal cracking/crazing, and curling.
Building codes such as the International Building Code (IBC) and International Residential Code (IRC) require minimum ventilation requirements based on square footage of the ventilated areas. In the IBC, Section 12.2.1 states, “The net free ventilating area shall be not less than 1/150 of the area of the space ventilated.” Reduction in the requirements can be reduced if ventilators, such as power vent fans, are located in the upper portion of the attic or rafter space. The IBC states, “Upper ventilators shall be located not more than 3 feet below the ridge or highest point of the space, measured vertically, with the balance of the ventilation provided by eave or cornice vents.”
