What grows on your roof?

The installation of green roof systems on top of buildings in urban areas has the potential to provide solutions to some of today's pressing issues, including rainwater runoff and local food production.

Appropriate technology students Hannah Wallach, Gina Butler, Sophie Dupont and Drew Leon are researching green roof systems and the best plants, soil and conditions that can be used for them. Their project is part of an independent study class in Appalachian State University's Department of Technology.

"Undergraduate research allows us to hone in on what we like and what we want to learn more about," said Wallach,a senior from Banner Elk. "I get to apply the knowledge I've learned in my lower level classes in a more creative and independent setting."

"With this research, we actually get to work with a green roof system," said Butler, a junior from Boiling Springs. "We get blurbs in class about them, but here we get to learn how to lay them out."

Two types of growth methods

The team is researching methods for growing both ornamental and edible plants on a green roof system. They are using intensive and extensive growth methods. Intensive growth means that the soil is deeper or the plants involved need more maintenance. Plants used in intensive systems include edibles, such as spinach, mint and basil. Extensive growth means the soil is relatively shallow. This is the growth medium generally used for ornamental plants including yellow moss, angelina and limelight.

Part of the team's research involves the application of biochar to the system's soil. Biochar is similar to charcoal but is used as a way to capture carbon rather than as a fuel. The team is looking at whether biochar helps maintain water and nutrient retention in the soil to help the plants to grow.

"This has given me the opportunity to learn and experiment with two subjects—biochar and green roofs—that are new and emerging industry technologies, and both provide great promise for the future," said Leon, a senior from Greensboro.

The team is also trying to determine the best growth medium for green roof systems that have the lightest weight. In order to install a green roof system, the roof of the building must have an existing load capacity that can carry the weight of the system, as well as rainwater the soil catches.

"Green roof systems can be expensive to install," said Dupont, a senior from Charlottesville, Va. "They can easily be integrated into new construction because there tends to be more money available for new projects than for retrofitting a building for a green roof system."

Educating the public

While researching the best growth methods, the team is also looking for ways to educate the public about the benefits of green roof systems.

"Green roof systems are not only aesthetic," said Butler. "They can be used to bring back native plants to urban areas, which will also increase the biodiversity of those areas. Green roofs bring people back to nature, as well, and can make them feel better. The systems also can provide plant nurseries as well as a place to produce food."

"There is a lot of potential to grow food on a green roof," said Dupont. "There are not a lot of areas to produce food in cities and green roofs would be a great place to do so. It could provide a solution to the food crisis some areas are starting to experience."

Wallach said the team hopes to encourage people in the local area to build their own green roof systems, if they feel they can do it. "There are places where the public can find local materials to build a system and if they have construction experience or friends that do, it's not impossible for them to do it," she said.