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.

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 tot he 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.

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.

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 properly