Gravity vents are often called globe vents or barn vents. They are a sturdy multi-use cap designed for flat or sloped roofs and have a metal band to prevent crosswinds and rain. All gravity vents have a built in screen for bugs and are available in small 4 inch sizes up to 48 inch (4 foot round connections) for industrial barn or warehouse venting. 

• Commercial Roof Gravity Ventilator Video