Types of roof vents
There are different types of roof vents and different strategies for achieving effective roof ventilation. Here's a brief overview:
Installed along the roof peak, ridge vents are probably the most important vents in any passive (non-electric) roof ventilation system. Hot air that accumulates inside the attic rises by convection and escapes outside through ridge vents. Not always easy to see, the openings for a ridge vent are the continuous space on either side of the ridge cap.
On an asphalt shingle roof, ridge vents are usually covered by a layer of shingles. The warmest air in the attic rises naturally to the roof peak and escapes outside through the ridge vents.
Soffit vents run parallel to the eaves along the soffit. These vents work with ridge and gable vents to promote good roof ventilation. Soffit vents may run continuously under eaves. Rectangular or circular vents may be installed in soffits where a continuous strip-type vent was omitted.
Installed along the eaves of the roof, these vents are usually in the form of grilles that run the length of each soffit. By admitting outside air into the attic as warmer air leaves the attic through higher vents, soffit vents play a major role in effective roof ventilation.
Installed near the peak of a gable end, this screened vent can allow hot air to leave the attic or fresh air to enter, depending on prevailing breezes and temperature conditions.
If attic airflow is insufficient, your roofer may recommend a gable end vent such as the one shown.
POWERED ATTIC VENTILATORS (PAVS).
Sometimes referred to as attic fans, PAVs come in several forms. Some are designed to be mounted on the roof, while others mount in the attic floor or the gable end. All PAVs contain an electrically powered fan (usually controlled by a thermostat) that exhausts hot air from the attic on hot summer days.
A PAV should not be necessary if a roof has properly sized and installed ridge and soffit vents. While a PAV will definitely exhaust hot air from the attic during hot weather, it consumes electricity, and can actually suck cooled air from the living space through leaks in the attic floor. For this reason, many home energy experts recommend passive roof ventilation over active ventilation with a PAV.