Roof Vent Aims To Prevent Wind Damage

As legislators debate the merit of adding wind-damage protection to the National Flood Insurance Program, new technologies are emerging to help make buildings in coastal areas safer from wind damage.

Hurricanes often lift roofs off buildings and expose them to damaging conditions, even after the worst of the wind has passed. Hurricane Andrew resulted in $26 billion worth of damage, and insurers are anxious to find means to mitigate similar losses in the future.

Virginia Tech University faculty members from the architecture and engineering departments as well as a graduate student teamed with a local roofer to devise an inexpensive vent—the V2T—that can reduce roof uplift on buildings during high winds, and even a hurricane. With the vent, low-sloped roof buildings around Wytheville, Va., where Virginia Tech alumnus Chuck Johnson and his brother, Pat Johnson, operate a roofing business, have sprouted the foot-high plastic structures that look vaguely like alien technology—a flying saucer connected by three narrow columns to a dome.

“Now, so many fasteners are required that roofing is expensive and the integrity of the deck is compromised,” Johnson says. But the V2T system could revolutionize the way roofing is done, Johnson says. “We are using physics instead of mechanical fasteners or adhesives. The harder the wind blows, the better it works.”

The physics involved is the Venturi effect, which posits that wind forced through an opening speeds up, such as through mountain passes and between city buildings. The V2T splits the airflow, speeding up the wind that is forced through the vent (between the upper saucer and the lower dome), which drops the pressure and creates a vacuum. The saucer has a hole on the bottom and the columns are tubes from the saucer to the dome and the underside of the roof membrane. The wind pressure draws the air out of the saucer and from under the membrane, pulling the membrane down tight against the substrate.

“The pressure being created under the membrane is lower than the uplifting pressure of the wind over the roof,” says Jim Jones, associate professor of architecture at Virginia Tech. “The result is a low-pressure condition that prevents the uplift and detachment of the roof membrane.”

Source: Virginia Tech University