In order to maintain appropriate moisture and temperature levels in the top portion of your home, proper attic venting is required. Venting your attic can be accomplished either mechanically or non-mechanically. Powered attic vents require electrical power and will likely produce some noise. Non-mechanical attic venting can be just as effective if it is done right, that is, in accordance with the shape and proportion of your home.
There are a couple of rules to remember when venting your attic. First, both intake and exhaust vents are necessary for proper ventilation. Cool air must be allowed to flow into the attic while hot air flows out. Heat rises, so your attic's exhaust vents must be placed higher up in the space. Secondly, figure on installing 1 square foot of ventilation per 150 square feet of attic space, divided up between intake and exhaust vents.
Hard-wired attic vents
One option you may consider is hard-wired vents that are powered electrically. These vents may be intake or exhaust vents depending on the fan's placement. When in operation, the vent either draws air in or blows it out.
Hard-wired vents are commonly installed in the gables of a house, but some domed or box roof vents are powered as well. They work well, in that, regardless of the weather, air will be moved through your attic. They can be controlled from a switch or by a thermostat/humidistat, and on the downside, they require wiring and they could be found to be a bit noisy.
There is, however a type of vent that is mechanically activated with the wind. The turbine vent is designed to be located towards the ridge of the roof to extract the air and it works best on windy days since it does require wind to work.
More common than mechanized vents are vents that work without the aid of a motor. There are numerous types of non-mechanical vents, including gable vents, ridge vents, soffit vents, and roof vents.
Gable vents, ridge vents, and high-positioned roof vents are used for exhaust purposes, while soffit vents and low-positioned roof vents work for intake. Both types are necessary for a properly vented attic, but not all roofs are able to take all types of vents.
Ridge vents run along the top edge or ridge of the roof where the faces meet. They typically run the entire length of the ridge in order to provide the most exhaust ventilation. Ridge vents make perhaps the best exhaust vent because no hot air can get trapped above them.
This type of vent works for exhaust, but because the gable is below the apex of the roof, pockets of hot air may avoid exhausting by rising above the vent. Gable vents are the type most likely to be motorized.
The soffit is also called the eave or the underside of the overhang. A continuous soffit vent installed along the underside of the overhang is the best means for intake ventilation, as cooler air continually moves into the attic through it.
Other roof vents
Dome or square-shaped roof vents are installed on the roof face itself. When higher up, they replace ridge or gable vents for exhaust. They are not commonly used for intake purposes.
Ridge, gable, soffit, and roof vents are the standard means of ventilating an attic space. Appropriate ventilation is necessary to keep temperature and humidity in the attic at reasonable levels. While powered vents are available and do the job, non-mechanical vents, when properly installed, are equally capable of ventilating an attic, and they neither require electricity nor possess a humming motor.