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Research / Discovery

Green roofs offer beauty, challenges in arid climates

August 4, 2010

Imagine a future where a natural, lush "living roof" is a standard feature on all new construction. In an effort to advance the possibility, scientists from the Department of Horticulture and Landscape Architecture, have been working to identify the best-suited plants and the bona fide environmental benefits to placing plants on top of conventional roofs.

Plant species performance, green roof benefits

Downtown Denver project

(6 images)

Edges of the Green Grid modular system on the EPA Region 8 roof in downtown Denver.

Weather station components are part of the EPA building rooftop design.

A view of some of the Sedum species on the roof.

A variety of plant species were tested.

Research plots were mixed in with the existing green roof.

Researchers from CSU's Department of Horticulture and Landscape Architecture have recently completed a green roof study, exploring the biological performance of plant species and growing soils and mixes in Colorado's arid climate.

Using the green roof atop Denver's Environmental Protection Agency Region 8 headquarters, researchers explored the effects of green roofs on:

  • stormwater quality
  • runoff quantity
  • mitigation of the urban heat-island effect (an effect in which metropolitan areas are significantly warmer than the surrounding rural areas)

Which plant species are best?

The EPA building, located in downtown Denver at 16th and Wynkoop, includes a three-terraced, 20,00-square-foot green roof. The "extensive" garden roof is a shallow, 4-inches deep. Plants chosen for the garden are hardy, low-maintenance species, designed to create a self-sustaining plant community.

A conventional rock ballast roof across the street on the Alliance for Sustainable Colorado building served as a control roof. Monitoring equipment for stormwater and weather stations are located at both the EPA building and the Alliance building to compare the differences between greened and conventional roofs.

Jennifer Bousselot, a Ph.D. student, along with Principal Investigator Professor James Klett and Research Associate Ronda Koski, received an Environmental Protection Agency Regional Applied Research Effort, or RARE, grant for the project. Results of the CSU research will be published in the near future and made available to the public through the EPA.

Benefits of green roofs

Green roofs can:

  • provide insulation and therefore reduce a building's heating and cooling demands
  • capture and potentially clean stormwater
  • create wildlife habitat
  • add natural, "living roof" beauty to cityscapes

By helping to mitigate environmental extremes common on conventional roofs (e.g., temperatures can reach upwards of 150 degrees on asphalt rooftops in the summer), green roofs help to lower urban air temperatures, mitigating the heat island effect.

"There needs to be more exploration on the value of green roofs in arid climates," Koski says. "Colorado and other arid climates have unique conditions that include the need to irrigate green rooftops."

Green roof on campus

The Fort Collins main university campus currently has a small, 400 square foot, green roof on the Microbiology building. Managed by Facilities, the area adjacent to the Microbiology Study Lounge includes various plants to:

  • reduce the heating and cooling loads on the study lounge
  • reduce stormwater runoff
  • filter pollutants out of the air

Future projects

If new funding sources can be found -- and ideally a successful multidiscipline collaboration formed -- additional green roof projects on campus may allow additional research while adding natural beauty and more "green" to Colorado State rooftops.

Interested in exploring the possibility of additional campus green roof projects? Contact Jim Klett at or (970) 491-7179.