Nebraska professor growing grasslands atop city buildings

Professor Richard Sutton surveys 6,000 sq. ft. of native grasses planted on top of the Larson Building in downtown Lincoln. (Photo by Ryan Robertson, NET News)
Richard Sutton designed the green roof atop the Larson Building with the rest of the roof's features in mind. He says his landscape architecture background is useful in cases like this, when the green roof will be enjoyed by the building's residents. (Photo by Ryan Robertson, NET News)
Richard Sutton developed a special mixture to plant the grass in. He calls it the "media," and it's made up of sand, expanded shale and compost. It's lighter than soil and retains more moisture. (Photo by Ryan Robertson, NET News)
Sandhills Publishing constructed the building housing their data center with the goal of it being LEED Gold Certified from the start. (Photo by Ryan Robertson, NET News)
This is one of three green roofs Sandhills Publishing implemented in their building's design. Richard Sutton uses this 450 sq. ft. area to help teach his students. (Photo by Ryan Robertson, NET News)
This type of green roof is known as "intensive" because it incorporates larger plants into the design. "Extensive" roofs typically only use simple vegetation like grass or sedums. (Photo by Ryan Robertson, NET News)
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August 22, 2013 - 6:30am

As more companies feel consumer pressure to be environmentally friendly, often times the price of going green can be too costly. One Nebraska professor, however, hopes to improve on an old idea by helping companies build for a greener future.

Looking out from atop the Larson Building in downtown Lincoln, the city skyline seems fairly vast, and full of concrete. There are plenty of hard-surfaced rooftops. Some black. Some white. Some have cars parked on top.

Photo by Ryan Robertson, NET News

Sutton planted a wide variety of native grasses on this green roof. He planted the seeds here two years ago in a specially formulated mixture which he calls the "medium". It's lighter than soil and more absorbant than standard soil, which helps slow runoff and allows the plants to absorb the moisture.

Image Courtesy of Green Roofs for Healthy Cities

This image shows the different layers required to install green roofs. Extensive green roofs are typically simpler, and more light weight. Sedums, drought resistant and hardy succulent, are the most common type of vegetation used. Intensive green roofs are more like a conventional garden or park with almost no limit on the type of available plants.

But the roof of the Larson building stands out like an island oasis in a concrete sea, as 6,000 square feet of prairie grass flourishes high above the city streets.

“I’ve got side-oats gramma, buffalo grass, blue gramma, hairy gramma, sand drop seed, little blue stem, and I’m starting to mix some forbs in as well,” Richard Sutton said, talking about all the different types of grass he planted on this roof two years ago.

Sutton is a professor at the University of Nebraska-Lincoln, where he teaches agronomy, horticulture, and landscape architecture.

For much of the year, his classroom is several stories off the ground, and his lessons focus on creating what are known as green roofs.

“It’s a nice blend of dealing with plants and also creating environments for people,” Sutton said.

Green roofs are defined as a “vegetative layer grown on a rooftop”. They can range from simple grasses to roof-top gardens. Some even have trees, much like the Hanging Gardens of ancient Babylon.

Regardless of size, they all have numerous benefits, like easing strain on a city’s storm drains during a heavy rain.

Photo by Ryan Robertson, NET News

The Lincoln skyline from atop the Larson Building. Professor Sutton estimates over 90 percent of the surfaces in downtown Lincoln contribute to excess runoff during rain storms because they are hard surfaces. Sutton says green roofs can slow that runoff, and cool the water. As he explains, when rain water hits a hard, heated surface it heats up as well. Heat in the water is a form of pollution and can harm the natural balance as the runoff makes its way to streams, rivers, or lakes.

“Think of [them] more as a sponge valve,” Sutton explained. “It rains, it soaks it up, gets on the leaves; but then when it reaches the point where we have more rain and it can’t absorb anymore, then you get it flowing through.”

If all the buildings in Lincoln had these “sponge valves,” Sutton said the city may never need to invest in storm drains ever again. However, he added it’s unlikely that will happen unless the city creates a storm-water utility.

“Which means you would be paying a fee based on the amount of hard surface you contribute—the more hard surface, the more the runoff—which means [you] have to pay more out of property taxes in bond issues and so forth to build bigger storm sewers,” Sutton said.

Aside from slowing runoff, green roofs aid in the fight against climate change as well, removing carbon dioxide and other pollutants which contribute to global warming. Also, through evaporation and a process called transpiration, where plants release moisture into the atmosphere, the air temperature around a green roof is cooler than a conventional roof.

These benefits help to counteract “heat islands”, which occur when a city’s asphalt and concrete absorb and radiate heat, making urban areas significantly hotter than rural areas.

While no one would confuse downtown Lincoln with downtown New York City, the effect can still be measured. However, Sutton pointed out the problem is much worse in New York, that’s why proponents are lobbying there for green roofs to a greater extent.

Photo by Ryan Robertson, NET News

Mike Peterson is the managing director at Sandhills Publishing in Lincoln. He says Sandhills' leadership approaches the environment like they approach the market, by assessing the needs and reacting. Sandhills has three green roofs on top of their data center building, which has been LEED Gold Certified by the U.S. Green Building Council.

Photo by Ryan Robertson, NET News

A rain water collector sits atop one of three green roofs at Sandhills Publishing's data center building. This roof sits over the data center's server room, and helps regulate the room's internal temperature. Peterson says while good for the environment, this green roof will also help lower the building's utility bill.

However, green roofs aren’t without their drawbacks. Even though they last three times longer than conventional roofs, they can be significantly more expensive to install. Anti-leak membranes, drainage systems and extra support for the added weight are just some of the factors which need to be accounted for in the total price. Insurance companies may also charge higher premiums for roof-top gardens.

“There’s substantial cost in putting up something like [green roofs], but there’s also long-term cost savings that you have with the building as far as energy and heating and cooling and things like that,” Mike Peterson said. He’s the managing director at Sandhills Publishing, an international trade-magazine publisher headquartered in Lincoln.

Peterson said his company feels a responsibility to the environment, and wanted their data center to be a LEED (Leadership in Energy & Environmental Design) Gold certified building.

To accomplish that goal, Sandhills installed three different green roofs on their data center building. One of those roofs is over the server room. The machines whir in unison, constantly crunching data for clients all over the globe.

As they go about their daily tasks, the servers generate heat. Peterson said delicate equipment like the servers need to be kept cool-- a constant and necessary cost of doing business for many companies.

Peterson said the cost of cooling the server room is less for Sandhills, though, because the green roof helps regulate the internal temperature of the room, much like the sod houses which dotted Nebraska’s countryside more than a century ago kept pioneers cool without the modern convenience of air-conditioning.

“This building allows us to respond to the environment and that responsibility we feel we have. It also allows us to respond to the community because we’ve been able to work with the University to have them take care of one of the green roofs and look at those native Nebraska grasses and how they grow,” Peterson said.

And it’s the use of native Nebraska grasses which Richard Sutton is banking on to help green roofs increase in popularity not just in Nebraska, but across the country.

Photos by Ryan Robertson, NET News

The native grasses planted on top of the Larson Building (pictured above) are out performing the sedums planted at the same time (pictured below). Sedum is a shallow root succulent which is drought resistant, and widely used in green roofs around the world.

In addition to the increased cost of installation, maintenance of green roofs can be costly and time consuming as well, because most use a plant known as sedum, which costs around $15 - $20 a square foot to install.

But Sutton said a green roof planted with Nebraska’s native prairie grasses, along with a specially formulated planting mixture, could bring that cost down to around $5 a square foot.

Native prairie grasses require very little maintenance, and only need to be watered once a week if there’s a drought.

Once the cost drops, Sutton thinks developers will be much more likely to install green roofs, and not just on commercial buildings. While his focus may be on urban areas at the moment, Sutton ultimately wants to make green roofs more affordable for residential homes as well. Like those sod houses on the prairie long ago, sometimes old ideas become new again.




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