Inexpensive roof vent could prevent wind damage

Hurricanes often lift the roofs off buildings and expose them to damaging conditions, even after the worst of the wind has passed. Now, a roofer, Virginia Tech architecture and engineering faculty members and a graduate student have devised an inexpensive vent that can reduce roof uplift on buildings during high winds.

Low-sloped roof buildings around Wytheville, Va., where Virginia Tech alumnus Chuck Johnson and his brother, Pat Johnson, operate a roofing business, have sprouted foot-high plastic structures that look vaguely like alien technology — a flying saucer connected by three narrow columns to a dome. Chuck Johnson, the pitchman, has persuaded a travel company, a government complex and a Nestle’s distribution center to use the Venturi Vent Technology (V2T).

Hurricane Andrew in 1992 changed the roofing industry, Johnson said. “Now, so many fasteners are required that roofing is very expensive and the integrity of the deck is compromised.” But V2T could revolutionize roofing, Johnson said. “We are using physics instead of mechanical fasteners or adhesives. The harder the wind blows, the better it works.”

The physics is the Venturi effect: Wind forced through an opening speeds up. Covered porches create a breeze. Winds blow harder through mountain passes and between city buildings. Moving cars split the air, so when a driver cracks the window to get rid of cigarette smoke, the lower pressure outside sucks the smoke out.

Sitting in their kitchen six years ago, the Johnson brothers asked, “What if we could split the wind blowing over a roof and create a vacuum to suck the roof down instead of up?”

The result was V2T. 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 pressure being created under the membrane is lower than the uplifting pressure of the wind over the roof. The result is a low pressure condition that prevents the uplift and detachment of the roof membrane,” said Jim Jones, associate professor of architecture at Virginia Tech.

The Johnsons took their idea to Virginia’s Center for Innovative Technology (CIT), which referred them to Jones. “Their concept was a tube shaped vent that would rotate to catch the wind,” Jones said.

With funding from the CIT and the Johnsons’ company, Acrylife, the team tested several prototypes. These tests demonstrated the ability of the vent to generate low pressure that could be used to counter the uplifting forces from high winds.

Topics Tech Virginia