Ballasted roofing systems are roofs in which a membrane is laid on the roof deck and held in place by the weight of concrete pavers or natural stones, such as river stones. While ballasted roofing systems don't meet current Energy Star guidelines for cool roofing options, they do meet the "cool roof" standard for Chicago, which has been one of the earliest adopters of rooftop gardens and other green roofing technologies.
In a ballasted roofing system, the same stones that hold the roof membrane in place also provide an insulating barrier against solar heat, much like an adobe building in the desert or an old stone farmhouse that stays cool inside thanks to its thick stone walls. Ballasted roofing systems are relatively inexpensive, and ballasted areas may be combined with rooftop gardens to reduce the overall cost per square foot of a landscaped roof [source: Hoff].
- Abernathy, Dick. "Evaporative Roof Cooling: A Simple Solution to Cut Cooling Costs." Proceedings of the Second Symposium on Improving Building Systems in Hot and Humid Climates, College Station, TX. September 24-26, 1985. (February 3, 2011)http://repository.tamu.edu/bitstream/handle/1969.1/6787/ESL-HH-85-09-14.pdf?sequence=3
- Heat Island Group. "High Temperatures." April 27, 2000. (February 1, 2011)http://eetd.lbl.gov/HeatIsland/HighTemps/
- Hoff, Jim. "Is Ballast Green?" Professional Roofing Magazine. October 2008. (February 4, 2011)http://www.professionalroofing.net/article.aspx?id=1368
- Levinson, Ronnen. Lawrence Berkeley National Laboratory. "Cool Roof Q&A." July 29, 2009. (January 30, 2011)http://www1.eere.energy.gov/femp/pdfs/coolroof_qa.pdf
- U.S. Department of Energy. "Energy 101: Cool Roofs" (Video). (February 2, 2011)http://www1.eere.energy.gov/multimedia/video_cool_roofs.html
- U.S. Department of Energy. "Guidelines for Selecting Green Roofs." July 2010. (January 26, 2011)http://www1.eere.energy.gov/femp/pdfs/coolroofguide.pdf
- U.S. Environmental Protection Agency. "Green Roofs." February 23, 2010. (January 28, 2011)http://www.epa.gov/heatisland/mitigation/greenroofs.htm
- U.S. Environmental Protection Agency. "Reducing Heat Islands: Compendium of Strategies - Cool Roofs." 2007. (February 1, 2011).http://www.epa.gov/heatisland/resources/pdf/CoolRoofsCompendium.pdf
- U.S. Environmental Protection Agency. "Reducing Heat Islands: Compendium of Strategies - Green Roofs." 2007. (February 1, 2011). http://www.epa.gov/heatisland/resources/pdf/GreenRoofsCompendium.pdf
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