When planners seek assurance of a venue's sustainability, they most often look to reduce the amount of paper and to make donations. However, they may not make it to the roof, where innovative technologies—or just plain sod—are changing the ways buildings are heated, lit, and cooled.
"Typically, a green roof has a waterproof membrane, a drainage layer, a filter fabric, growing media, and plants," explained David Sailor, Ph.D., Portland State University, and principal investigator for A Green Roof Energy Calculator. "The growing media is usually composed of a lightweight aggregate, sand, and a small amount of organic matter." Sailor, along with Graig Spolek, Ph.D., Portland State University; Brad Bass, Ph.D., University of Toronto; Steven Peck, Green Roofs for Healthy Cities; Oregon Best Signature Research Center; and Environment Canada, was recently awarded a research grant by the U.S. Green Building Council (USGBC) to create an easy-to-use design tool that will assess the building energy use implications of green roof design decisions. "Green roofs typically cost significantly more than conventional roofs," said Sailor, "but evidence suggests that their extended lifespan compensates. Further, green roofs can save electricity for cooling in summer and heating in winter. They also have many other benefits, such as aesthetic appeal, biodiversity, carbon sequestration, urban heat island reduction, and storm-water runoff reduction."
According to the Greenroofs Projects Database, there are 732 green roof projects under way globally, comprising almost 17 million sf of area. Hospitality projects include the Vancouver Convention Centre expansion, the Hilton Baltimore Convention Center, Chicago's McCormick Place, Dubai's Burj Al Arab Hotel Helipad, Kauai's Princeville Hotel, the Four Seasons Boston, the Crowne Plaza Northstar in Minneapolis, and the Futures Inn Hotel and Conference Centre in Guelph, ON.
Unlike solar-panel-equipped roofs, where energy is stored in batteries, the energy benefits of green roofs are harder to gauge. "Green roof cost is proportional to surface area," said Sailor. "Green roof benefits generally also scale with surface area. There may, however, be issues related to economies of scale for purchasing and installing (as with most other products). Also, for taller buildings, the added cost of moving materials vertically up multiple stories may be a consideration." A sample output from the Green Roof Energy Calculator has charted a temperature comparison between a conventional roof and a sedum green roof, with the result that the latter is several degrees cooler in summer.
But climate control is not the only impact green roofs have on their occupants. The McCormick Place West Rooftop Garden—where 40,000 plants have greened approximately 15 percent of McCormick's 1 million sf of rooftop—is an ideal spot for special events, according to Metropolitan Pier and Exposition Authority spokesman Scott Winterroth. "This attractive building amenity offers spectacular views of the city and can accommodate up to 800 people for receptions and 300 for a sit-down event," he said.
At several properties in the green-conscious Fairmont Hotels chain, chefs are raising edibles. The oldest of these projects began in 1998 at the Fairmont Royal York in Toronto, said spokeswoman Sabrina Bozek. Rosemary, lavender, lemon thyme, parsley, and basil are just a few of the herbs growing in the 17 four-poster beds and 23 planter pots on the Royal York rooftop, which is also a place for chef-hosted culinary explorations for meeting groups.
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