Do Roof Ventilators Work?

Functionality

• Experts agree that roof ventilators do, in fact, work. That does not mean that every roof ventilation system will work well for your attic. How well your roof ventilation functions depends on the type of system you use and the manner in which it is installed.

Net-Free Vent Area

• If you want your roof ventilation to function well, pay attention to the size of your vents. You need 1 square foot of net-free vent area for every 300 square feet of attic floor. Net-free vent area is a measurement of the amount of open space in your vent -- that is to say, the area of your vent that is not blocked by baffles. Half of this is for the intake vents, half for the exhaust vents. For example, if you have a 900 square foot attic, you need a net-free vent area of 3 square feet. The exhaust and intake vents should each have 1.5 square feet of net-free vent area.

Placement

• For your roof ventilation to work, place the exhaust vents along the ridge of your roof and the intake vents along the eaves. If you just place multiple vents along the ridge, air will just be cycled between the vents, leaving the air in the rest of the attic unmoved. A similar problem can occur with placing multiple vents along the slope of the roof.

Types

• There are a number of types of roof vent. Static pot vents simply provide an opening for the air to flow through. Continuous ridge vents are similar to static pot vents, but they have openings all along the ridge of the roof. Fan vents use an electric fan to keep the air moving. Some of these use solar power to run the fans. Turbine vents use natural wind to suck air up from the attic without electricity. Soffits are intake vents, designed to be placed along the eaves of your house.

Pros and Cons

• Static pot vents work, but they may not work very fast. Continuous ridge vents do not work well without soffits. Fan vents work well but consume electricity. Solar fan vents do not work at night. Turbine vents work day or night and consume no power. When the wind blows, it pushes on the propeller blades, causing them to rotate. This draws up air from the attic below. A turbine ventilator that is 1 foot across can exhaust approximately 350 cubic feet of air from your attic every minute with just a 5 mile per hour breeze. This will empty even a 15,000 square foot attic in under an hour.