Types of Ventilation

Your existing attic ventilation may not be adequate. Problems common in improperly ventilated attics are mold, excessive heat, and ice dams. The correct ventilation types are an important part of a successful solution. They move air through the attic, creating good ventilation and proper air flow.

Roof Louvers

Roof louvers are installed as close to the roof ridge as possible to release of moisture and overheated air. Because they’re installed near the ridge, they provide a continuous airflow along most of the underside of the roof sheathing. The airflow pattern isn’t uniform, however, so for maximum effectiveness, vents should be spaced equally along the roof.

Roof Louver ventRoof Louvre 2
A roof louver is an exhaust vent located near the ridge.Fifteen roof louvers are required to equal the exhaust venting of 42 linear feet of ridge vent.
Ridge Vent Attic Ventilation
This clearly demonstrates the performance and aesthetic advantages of ridge vents.

It’s important to emphasize that the advantages listed above apply only to ridge vents that use external baffle design. A series of independent tests has concluded that only an external baffle can direct the wind up and over the vent. That’s significant, because it’s that controlled flow of air that creates the area of low pressure that causes air to be pulled from the attic.

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Gable Vents

Gable louvers are typically installed in the gables. Two types are available, rectangular and triangular. In most installations, a unit is placed at each gable end.

Note: Sometimes louvers are installed in opposite gable ends, without intake venting in the mistaken assumption that a good “cross flow” of air can provide adequate ventilation. What typically happens, however, is illustrated below. If wind direction is perpendicular to the ridge, the louvers act as both intake and exhaust vents. If the wind direction is parallel to the ridge, a cross flow of air is established, although the flow tends to dip toward the attic floor, leaving the hottest air still at the underside of the roof sheathing.

Gable Vent Louvre
A gable louver, an exhaust vent, allows unwanted air to flow out of the attic. These are located at the ends of the attic.
Attic Ventilationgable vents parallel to the ridge vent
With wind blowing perpendicular to the ridge, the louvers act as both intake and exhaust vents.With wind blowing parallel to the ridge, airflow dips towards the attic floor, leaving the hottest air still on the underside of the roof sheathing.

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Wind Turbines

Technically, wind turbines aren’t a fixed ventilation system because they use a moving part to help exhaust air from an attic. That moving part consists of a series of specially shaped vanes that turns wind force into a rotary motion. The spinning vanes gain velocity that create an area of low pressure. That low pressure, in turn, pulls air from an attic.

Although not as effective as ridge vents, wind turbines provide a low-cost alternative in areas where consistent wind speeds of at least 5 mph are typical. Without that minimal wind speed, wind turbines act essentially as roof louvers. When the wind is blowing, however, wind turbines can be effective air movers.

To provide maximum ventilation benefits, wind turbines, like roof louvers, must be equally spaced along a roof. Otherwise, ventilation will be focused in the area surrounding the wind turbines, allowing hot spots to develop in other areas of the attic.

wind turbine
Wind turbines are located near the ridge and are used to exhaust air from the attic.

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Attic Fans

For the most part, a power fan is a motor-driven version of a wind turbine.

A power fan uses the rotary motion of blades to pull air into the attic through the intake vents at the soffit or near the roof’s edge and exhausts it out of the attic near the ridge. But instead of using wind power to drive the blades, power fans use electricity to drive high-efficiency motors or sunlight if that are solar powered.

Unlike a wind turbine, however, the effectiveness of a power fan isn’t dependant on wind force. Instead a power fan is turned on and off as needed, automatically, with thermostat and humidistat controls. (In some models, an integral humidistat control is standard; in most models, however, a humidistat is an add-on option).

Depending on the size of the motor and the efficiency\ of the blade design, power fans can move more than 1,500 cubic feet of air per minute (CFM). That high volume of air movement is critical. To ensure adequate ventilation, power fans must provide at least 10 changes
of attic air every hour.

Although a power fan can move a large volume of air, a single unit generally cannot “vacuum” all hot air from an attic. Usually, to provide uniform air movement along the underside of the roof sheathing, a series of power fans must be spaced equally along a roof.

When evaluating the feasibility of using power fans, it’s important to evaluate one factor which is considered to be a major disadvantage: namely, that power fans cannot vent away moisture during winter unless they are equipped with humidistat controls.

If this is a problem in your climate, it can be solved by using a power fan that has a humidistat control. When that’s done, power fans do offer key benefits. For one, they ensure a high volume of airflow; even on days when outside air is virtually still (a common occurrence in inland areas on hot summer days).In addition, power fans provide ventilation in some circumstances where fixed systems would prove inadequate. Most static exhaust fans in a hip roof application fail to meet ventilation code requirements for high (exhaust) vents, while power fans can provide the air needed to ventilate the attic properlyattic fanPower fans are used to move large volumes of air- a good option for hard-to-vent hip roofs that have limited horizontal ridge length available for ridge venting.

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Drip Edge Vents

Beware of drip edge style vents combined with gutters. In the winter, the gutter may fill with snow, completely blocking the vent and making the vent ineffective.Ventilation types - Drip Edge Vents

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Roll Style Ridge Vents

Ridge Vent-Roll Styleroll style ridge vent
A roll vent with an internal baffle or without any baffle at all, does not “pull” air from the attic.An externally baffled vent “pulls” air from the attic from both sides of the ridge vent.

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Improperly Vented Bath Fans

Bathroom fans are used to remove excess humidity from your home. Opening the window or leaving the door open will not work.

Well installed bathroom fans should:

  • Have timers so that they run for several minutes after the shower is shut off to remove excess moisture.
  • Vent through the roof or gable, not into the attic or the soffit.
  • Have the shortest possible ductwork to let the fan work at its best.

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Improperly Installed Ridge Vents

Ridge vents need to be installed properly to work. Some common installation mistakes are listed below:

  • The slot in the roof sheathing should be at least ¾” wide on each side of the ridge.
  • Felt paper and/or shingles should not block the vent.

The slot in the sheathing must be visible from the attic
– many times the vent is installed, but the slot is not cut
!

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Improperly Installed Soffit Vents

Soffit vents need to be installed properly to work. Some common installation mistakes are listed below:

  • Not enough soffit ventilation
  • Round button style vents rarely allow enough air to enter the attic
  • Vinyl soffits even when perforated may have a wood soffit underneath which will not allow any air into the attic
  • Insulation may be blocking the soffit vents from the attic.

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Improperly Vented Clothes Dryers

Dryer vents need to be vented to the exterior in the easiest way, otherwise the hot air may not exhaust to the exterior and may wind up in your house creating problems such as excess moisture, mold, etc.

Some common mistakes with dryer venting are:

  • Long duct runs with many elbows and turns
  • Vents exhausting into attics or out roofs.

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Wet Basements

Water, humidity, and moisture from a wet basement can easily migrate to your attic and cause problems such as mold, rot, etc.