The roof ventilation rage over the past 15 years has been continuous ridge and soffit ventilation. These systems are nearly invisible and they create a system through which air enters your attic space and then gently floats through the attic space. No matter what the time of year, the air exits the attic space through small gaps at the peak of the roof. These gaps are covered with any number of different products that allow air to pass, but prohibit rain, snow and insects from entering your attic area. You can't see these vents as they are almost always covered by the roofing shingles at the peak.

The mechanics of the air movement are quite simple. During warm weather, the air inside your attic heats up. Since warm air rises, it tends to float out of the high ventilation spaces. This convection movement naturally draws in cooler outside air to replace the air that just exited.

Wind that blows across the roof anytime of year also acts to vacuum air from the attic space. The wind blowing across a roof can create a partial vacuum on the leeward side of a roof. When the wind blows and at the right angle a significant amount of air can be pulled through the attic space.

But in my opinion, there is a better ventilation method that pulls vast quantities of air from an attic space no matter which direction the air blows. I am speaking of traditional wind turbine vents. Some people call these whirlybird vents. They are round metal vents that have fins in them and stick up from the roof surface perhaps 18 - 20 inches. The fins are located in a dome-shaped housing that spins each time the wind blows across it. The faster the wind speed, the faster the turbine rotates.

Turbine vents have been used for many years in both residential, commercial, agricultural and industrial buildings. The vents are very affordable, easy to install, and they pump vast amounts of air from attic spaces.

A small 12 inch diameter turbine vent with a constant wind speed of 5 miles per hour (mph) can remove 347 cubic feet of air per minute (cfm) from the attic space. A single 14 inch diameter turbine vent that is subjected to 15 mph winds can expel up to 1,342 cfm of air! If the winds are still, the vents still allow air to drift up and out of the attic space, although not nearly as much.

Those amounts of air might not mean much to you at first blush. But consider a moderately sized home whose attic space is 36 feet deep, 50 feet long and 10 feet high at the peak. This attic space contains 18,000 cubic feet of air. The single 12 inch diameter turbine vent could provide a complete change of air in the attic space every 52 minutes if the outside breeze was just 5 mph. The 14 inch diameter unit could provide a complete air change in the attic every 14 minutes at 15 mph. Imagine what happens if you install two or three of these simplistic turbine vents on the back side of your roof out of view?

Many people look at the vents and think they will leak during a rainstorm. The wind that almost always accompanies a rain shower or storm actually causes the turbine to spin and blow rain drops away from the vent. The same is true for snow.

The roofer your builder hires can install a turbine vent in less than 15 minutes. The average cost of a high quality turbine vent is just $50. The best ones provide years of maintenance-free service since they have permanently sealed ball bearings.

If you want the strongest turbine vent, be sure to buy one that has external braces. These are simple metal braces that extend out beyond the spinning turbine. These visible braces do a fantastic job of stabilizing the turbine when the winds are really blowing.