Green (or Vegetated) RoofsMenu:
The green roof of the 12-story Chicago City Hall building
Photo courtesy of Katrin Scholz-Barth (NREL PIX number 13397)
Green roofs are essentially a rooftop that is covered by a water-proofing layer, followed by a layer of soil and finally native plant(s), typically a variety of sedum. There are two types of green roofs, Intensive and Extensive.
Intensive green roofs are an older, traditional-style rooftop garden, with large trees and shrubs. They often are accessible to the public and can include garden paths, seating, and other features that make the roof more like a park. As suggested by the name, they are labor-intensive, requiring irrigation and continuous maintenance. Intensive roofs are multi-layer constructions, typically installed over concrete roof decks. They require substantial structural capacity: approximately 8 inches to 4 feet of soil depth, and support of roof weight loads from 80-150 pounds per square foot (University of Florida, IFAS Extension).
Extensive roofs, on the other hand, are not designed for public use but for environmental benefits. They help to mitigate the effects of storm water runoff by filtering, absorbing and/or detaining rainfall. Extensive green roofs can have a soil depth of approximately 1 to 7 inches and can carry weight loads of 15 pounds per square foot. They are constructed of a lightweight soil medium and are underlain by a drainage layer and a high quality impermeable membrane that protects the building structure. Extensive green roofs can be installed during the construction of a new building or retrofitted on existing roof decks. However, a structural engineer should always first inspect the structure to determine its weight load limitations. (University of Florida, IFAS Extension)
Green roof technology is somewhat new in the United States, but has been used for decades in other parts of the world. Germany has been developing the technology since the 1980ís and green roofs cover 150 million square feet in Europe (Environmental Design & Construction). Tokyo requires the use of green roofs on all new construction (Environmental Design & Construction). However, the use of the technology in the United States is drastically increasing everyday.
Green roofs are becoming one of the most effective green building measures as they do much more than mitigate the effects of urbanization on water resources. They also extend the life of the roof, keep the building cool in summer and warm in winter, provide wildlife habitat, reduce the urban heat island effect, provide a sound buffer, absorb carbon dioxide and create aesthetically pleasing green space amidst the surrounding concrete.
Michigan has seen quite an increase in the use of green roofs in new construction projects, as well as renovations. A few notable projects in the Grand Rapids area are as follows:
- Cathedral Square- 4,800 square foot LiveRoof green roof
- Grand Rapids Ballet- 7,220 sq ft LiveRoof system
- John Ball Zoo- 1,500 square foot LiveRoof green roof system
- MLK Jr. Leadership Academy- 1,302 square foot XeroFlor system
- Kent County ISD- 6,456 sq ft XeroFlor system
- Burton Middle School- 1,400 sq ft LiveRoof green roof system
- East Hills Center (of the Universe)- The Center has a 7,140 square foot American Wick Drain green roof system with 3 varieties of sedum.
- The Helmus building- 2,511 square foot Carlisle-Syntec system planted with sedum
- Wege Plaza (part of the City of East Grand Rapids Complex off Reeds Lake)- 8,256 square foot roof with 9 varieties of sedum. The roof was installed by Aeroroofing and Bakhuycen Landscaping to waterproof the building and the area contains terracotta paving tiles made from 12,000 recycled tires.
- Metro Health Hospital (Wyoming)- 48,500 square foot vegetated roof, designed by Bazzani Associates. The Hortech system (called "LiveRoof") was installed by Katerberg and VerHage.
- Rapid Central Station- The 15,600 square foot (sectioned) green roof system replaced a faulty system installed on the Rapid in 2004. Installed in June 2008, the tray/modular green roof system (LiveRoof) was manufactured by Hortech in Spring Lake, Michigan.
Here is a listing of green roofs in Michigan:
- Blue Cross Blue Shield (Detroit)- 52,300 square foot XeroFlor system
- Warren Fire Station (Warren)- 13,500 square foot XeroFlor system
- US Border Station (Sault Ste. Marie)- 20,000 square foot XeroFlor green roof
- Mallet Creek District Library (Ann Arbor)- 13,000 square foot Roofscapes system
- University of Michigan Kresge Library (Ann Arbor)- 12,439 sq ft XeroFlor System
- Bell's Brewery (Kalamazoo)- 12,000 square foot green roof
- LaSalle Bank (Troy)- 38,513 square foot system
- Cooley Law School (Auburn Hills)- 20,000 square foot LiveRoof System
- Haworth's Headquarters (Holland)- 45,000 square foot LiveRoof System
- Mallets Creek District Library (Ann Arbor)- a 13,000 square foot Roofscapes System
- Battlecreek Public Safety Building- a 12,000 square foot Xero Flor green roof system
- Lawrence Technological Institute(Southfield)- 13,000 square foot green roof designed by HarleyEllis
- Ford Motor Company (Dearborn)- A 454,000 square foot Xero Flor green roof system. The roof, recognized by the Guiness Book of World Records as the largest green roof in the world, features sedum that can absorb 4 million gallons of rainwater annually.
Check out the resources listed below for additional information on green roofs!
Emory Knoll Farms is a leading supplier of plants and plant expertise for extensive green roof systems. Their R&D pages offer access to University studies on green roof applications along with photo galleries from each project.
This site is a good source for information regarding cities and government entities that encourage sustainable building design & greenroof projects.
Green Roofs for Healthy Citiesí mission is to increase the awareness of the economic, social, and environmental benefits of green roof infrastructure across North America and to rapidly advance the development of the market for green roof products and services.
Check out their site to learn more about green roofs, conferences and training courses in the arena of green design!
This site offers a wide range of interesting and informative links pertaining to Chicago's green roofs. It includes a description of Chicago's Rooftop Garden, first planted in 2000 on top of the 11-story City Hall building. The web site gives a description of the construction, design, and maintenance of the garden, and also includes many fascinating pictures.
The Low Impact Development site provides visitors with lots of useful information on green roof technology, including an introduction, maintenance and cost information, benefits, pictures, and specifications.
The Michigan State University site provides a variety of resources related to green roofs, including a basic introduction, research, funding, publications, photographs, and much more.
This is a great site to learn the basics of green roofs or gather more detailed information on the technology. The Center's site lists benefits, provides information on recent research, news, publications, links, and brief case studies.
Funded by the Steelcase Foundation of Grand Rapids, Michigan
Header photo by Carol Y. Swinehart, courtesy of Michigan Sea Grant Extension
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