Roof vents
Air intake and exhaust vents are used in ventilating steep-slope roof assemblies
to provide a means of allowing outside air to enter and exit attics and ventilation
spaces.
Intake Vents: Air intake vents are used to allow outside air to enter into attics
and ventilation spaces. Intake vents should be located along a roof assembly's lowest
eave at or near soffits or eaves.
Intake vents are best used with exhaust vents that are located at or near a roof
assembly's peak. This configuration of ventilation air intake along low points and
exhaust at high points takes advantage of natural convection.
Some of the more commonly used products are:
- Continuous soffit vents
- Individual soffit vents
- Drip edge or eave vents
A variety of pre-manufactured products are available for use as eave and soffit
vents. Some examples are shown here.
Figure: Examples of intake vents
Intake vents always should be installed to allow free movement of air into the ventilation
space and should not be blocked on the interior side by insulation or other material.
Baffles placed between rafters keep insulation from blocking air intake. Intake
vents must also be designed and installed to prevent precipitation, animals and
insects from entering the ventilation space. Drip edge vents should not be used
with gutters.
NRCA does not recommend the use of drip edge vents as intake vents in northern climates
where there is a likelihood of ice damming.
Exhaust Vents: Air exhaust vents are used to allow air in attics and ventilation
spaces to exit to the exterior. Exhaust vents should be placed at or near a roof
assembly's ridge or high point.
Exhaust vents are best used with intake vents that are located along a roof assembly's
lowest eave, at or near soffits or eaves. This configuration of balancing air intake
along low points and air exhaust at high points takes advantage of natural convection.
Some common types of exhaust vents are:
- Ridge Vents: Ridge vents are installed along the length of a ridge. Ridge vents
are either shingle-over or nonshingle-over types.
Figure: Example of shingle-over ridge vent
Figure: Example of nonshingle-over ridge vent
Shingle-over ridge vents are covered with shingles to prevent precipitation from
entering a building. Because the shingles used over the vent match those used on
the roof, shingle-over ridge vents are typically less noticeable than other types
of exhaust vents.
Because the exposed exterior material of nonshingle-over ridge vents is different
from the adjacent roof covering material, nonshingle-over ridge vents may be more
noticeable.
- Static Vents: Static exhaust vents are individual vents that are installed near
the ridge of a roof.
Figure: Examples of individual static exhaust vents
- Gable-end Vents: Gable-end vents are installed in the walls of a building at the
gable end's peak.
Gable-end vents are best used with intake vents at soffits or eaves. This allows
for air intake at the soffits or eaves and air exhaust at the gable-end vents.
Figure: Attic ventilation configuration with gable-end vents and intake vents at
soffits or eaves
When gable-end vents are used without additional intake vents located at a roof
assembly's low points, gable-end vents function as intake and exhaust vents, depending
on the wind direction. Additionally, their effectiveness depends on wind speed and
direction; they are more effective when wind is of a sufficient speed and coming
from a direction perpendicular to the roof assembly's gable ends. Gable-end vents
are of limited effectiveness when winds are light and/or coming from a direction
parallel to the roof assembly's gable ends.
- Turbine Vents: Turbine vents rely on wind to rotate the vent's turbine fan blades,
which draw air from the ventilated space. This vent design draws air from the ventilated
space at a greater rate than a static vent when wind is present. The amount of air
movement developed is a function of wind speed, as well as turbine size and efficiency.
Figure: Example of a turbine vent
- Powered Vents: Powered vents are essentially roof-mounted exhaust fans that are
used to exhaust air from a ventilated space. Powered vents can improve air movement
and should be mounted near the ridge. Powered vents are best used with intake vents
located at eaves or soffits
Powered vents may be controlled by thermostat and/or humidistat switches that cause
the vents to run only above a predetermined temperature or relative humidity. Powered
vents also should have a manual override.
Powered ventilation should not be used in combination with ridge vents or static
vents placed near a roof's ridge. In many instances, the air volume being exhausted
by the powered ventilation will result in air intake and, therefore, possible moisture
infiltration through ridge vents or static vents.