JUSTIN COOK The Roanoke Times

Virginia Tech senior Kevin Harris (left) hands fellow senior Jen Bowry a sedum to be planted on Seitz Hall as part of the green roof project. Green roofs are popular in other countries, especially Germany, but are just catching on in the United States.

BLACKSBURG -- Virginia Tech senior Stephanie Worthington doesn't have to look any further than her hometown of Arlington to see the effects of urban sprawl.

The term "heat island" -- used to describe the phenomenon of large stretches of pavement and buildings trapping heat -- seems like it was invented to describe the Washington, D.C., area in the summer.

Her interest in "green roofs," an innovation to combat that problem, landed her on the roof of Seitz Hall on Thursday morning, passing small water-efficient plants called sedums to fellow classmates so they could vegetate a 250-square-foot area.

"We're taking down forests so we have to kind of pseudo put them back somewhere," the urban forestry major said. "And this is a start."

Worthington was one of 20 Tech students and four students and two faculty from Nova Scotia Agricultural College to participate in a weeklong practicum taught by Tech horticulture professor Greg Welbaum. Classes and field trips to understand the design and benefits of green roofs culminated in the construction of one on Thursday.

Green roofs are popular in other countries, especially Germany, but are just catching on in the United States. They're becoming popular in Chicago and D.C., Welbaum said.

In addition to mitigating the heat island effect, studies have shown green roofs can increase building efficiency, filter rainwater and extend the life of the roof. They also provide another area for plants to grow and absorb carbon dioxide, a greenhouse gas that causes global warming.

But they're not cheap. The roofs cost $15 to $20 per square foot to install. So Welbaum had to be creative with the project.

Riverbend Nursery in Riner donated the plants. Membrane to plant the sedums was provided from surplus from the university's only other green roof, the new life sciences building. John Beegle of Beegle Landscaping and Lawn Care in Floyd oversaw the construction.

Constructing a green roof isn't as simple as throwing some soil and plants on top of a building, Beegle said. Shade can be an issue, as can the weight created by the plants. Several layers of materials, used to absorb and release the right amount of water and drain it off the side of the roof, are needed. Beegle described the drainage board as something resembling an egg crate with cups to hold only the water the plants need.

The plants themselves need to be hearty and able to go long stretches without rain. Upkeep includes watering the plants if they go for more than a month without rain and weeding the area, Welbaum said. Tech's horticulture club has volunteered to help with that work.

This is the fourth year the horticulture department has offered a one-week practicum before the start of classes. It's part of a $250,000 grant involving the U.S. and Canadian departments of education to encourage exchange student opportunities among North American countries. Nova Scotia Agricultural College has sent six students to Tech in the past four years to study for a full semester.

There was a connection between Tech and Nova Scotia Agricultural College before the project. Jerzy Nowak, the head of Tech's new Center for Peace Studies and Violence Prevention, was head of the horticulture department at the Canadian school before coming to Tech. Nowak met his wife, Jocelyne Couture-Nowak, while at the school. She was killed in the April 16, 2007, campus shootings.

Norman Goodyear, a professor at Nova Scotia Agricultural College, said it's great to have a relationship with Tech and get down to Blacksburg, the home of his former department head.

"That international exposure for students, whether it be here in Blacksburg or Mexico, is really critical," he said. "Not only for students, for faculty, too."