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Daniel Minkoff of The Minkoff Group was so convinced that his new 70,000-square-foot downtown Mountain View office building at 899 West Evelyn Avenue needed a green roof that he returned to the city in 2011 to adjust his 2009 entitlements. After speaking to prospective tenants in downtown Palo Alto and Mountain View, he found that “they wanted to stay in Caltrain-served downtowns, but they needed an outdoor amenity space.” The 13,000-square-foot rooftop garden includes two 15-foot mature trees, a bocce court, lawn, deck and trellis. The additional weight required some special steel support in the building. “You can take your lunch and a laptop up to the roof deck, and it is another place to work while still being able to walk to Caltrain to get home at the end of the day,” he said.
Nuance Communications Inc. agreed in April 2012 to lease the building for 12 years, paying net effective rents of $5.20 a square foot, according to Cassidy Turley Commercial Real Estate Services. Nibbi Bros. was the general contractor.
The city of San Francisco is stepping up its look at using roof vegetation to better manage storm water. Dense urban areas are full of impervious surfaces so there often are “no other opportunities for dealing with storm water rather than on the roof,” said Mark Palmer, senior green-building coordinator for the Department of the Environment.
In 2010, the city put in a 10,000-square-foot green roof on an eight-story city-owned office building at One South Van Ness Ave. The roof has sharply reduced the amount of runoff sent into the city’s sewer system. Sensors and emitters placed in the soil measure dryness and trigger watering during the dry months. Rainwater from an upper roof is collected and stored in a 6,500-gallon cistern on the living roof. The stored water has supplied 40 percent to 50 percent of the irrigation water used annually, Palmer estimated. The roof, which is accessible by a freight elevator to maintenance and operations staff, has attracted hawks, owls, dragonflies, ladybugs and grasshoppers.
First Community Housing, a San Jose nonprofit that develops affordable housing, has committed to green roofs. Two of its 18 buildings have living roofs and another will have one when construction is complete in November. So will three of the four new buildings it plans to build after that.
At downtown San Jose’s Casa Feliz, a LEED Gold building with 60 apartments, five green roofs manage storm water onsite rather than dumping large amounts of runoff into city sewers. The roofs retain 90 percent of rainwater, while the remaining 10 percent drains into a bio-swale, a vegetated soil area in the backyard that filters the water before releasing it into sewers through mid-sized pipes. The green system cost $320,000 to build—less than the $350,000 it would have cost to build a larger piping system to carry a much greater amount of water two blocks directly to the city’s sewers. “I’d rather put the money into our own building than storm piping in the street,” said Jeff Oberdorfer, First Community executive director.
At its 100-unit Fourth Street Apartments, also in San Jose, there is a 50,000-square-foot green roof that captures most storm water. Excess water goes into a concrete basin with sediment filters that treat the water before it is sent to the sewer system. “This is basically for low-impact development to maintain the water onsite. Many cities have low-impact development guidelines. You’re going to be required as a developer to do this sooner or later,” said Oberdorfer.
Photography by Laura Kudritzki