It has colonies of African penguins and Philippine coral, a four-story tropical rainforest and a digital planetarium with live feeds from NASA, but one revelation at the new California Academy of Sciences (CAS) museum in San Francisco is overshadowing all of those: the building.
Developed at a cost of almost $500 million and crowned with a "living" roof that itself functions as a chief exhibit, the 400,000-square-foot structure was designed to LEED Platinum specifications and is already being called the most environmentally advanced museum ever constructed.
Its grand opening on Sept. 27 took on the air of a Hollywood premier, drawing tens of thousands of people, including San Francisco Mayor Gavin Newsom and famed architect Renzo Piano, the Pritzker laureate who designed the museum. It filled to capacity in less than two hours.
Many of the structure’s most eco-friendly features won’t be recognized -- or possibly seen at all -- by the public. For instance, more than 30,000 tons of sand displaced during the site excavation was reused in dune restoration projects in San Francisco, and almost three-fourths of the building’s insulation is from recycled blue jeans, which is more effective at holding heat and reducing sound than conventional insulation.
But the building’s most obvious green feature was on full display. That would be its roof: a two-and-a-half-acre tundra that is an extraordinary scientific and engineering feat even by the standards of CAS, one of the nation’s esteemed scientific institutions.
Architecturally, every part of the roof plays some role in helping the building to function. Seven inches of soil and a field of native plants blanket the top of the building, lowering heating and cooling bills by providing natural insulation and reducing rainwater runoff by several million gallons each year. Sixty-thousand photovoltaic cells frame the outside edge of the roof, providing up to 10 percent of the building’s annual electricity needs.
Three large swells situated triangularly near the center of the roof act as domed ceilings for several exhibits inside, and are pocked with skylights that can open like valves to let warm air inside the building escape.
Encircled by the swells is an enormous window overlooking the museum’s piazza that opens at night to let cooler air in: another way the building is able to ventilate naturally.
One of the chief obstacles to the mounds, which rise at steep 55 degree inclines, was figuring out how to plant them. "The main challenge in putting this living roof together was finding a way to make sure that the soil on these slopes would not slough off," Frank Almeda, a CAS senior botanist, explains in a video posted on the organization’s Web site.
To do this, CAS installed a wire grid on the mounds that holds a network of square, tile-like "BioTrays" designed by Rana Creek Living Architecture, an environmental restoration consultancy based in California.
Made of tree sap and corn husks, the trays prevent soil erosion but allow plant roots and water to pass through. Eventually, Almeda says, the roots growing out of one tray will interlock with those growing from neighboring trays to bind all 50,000 squares together.
To make sure the roof endears itself to the surrounding Golden Gate Park, scientists spent two years testing 30 native plant species to determine which ones would thrive in local conditions, which include high winds and salt spray from the ocean. Nine species were selected, and almost 2 million of those plants now cover the roof.
But it’s more than just a garden. The roof’s surface temperature is 40 degrees cooler than normal roofs, helping to keep the building temperature about 10 degrees cooler than in other buildings. Overall, the museum is consuming 30 percent less energy than is called for under federal codes.
"The Academy of Sciences leadership was truly visionary in making this building a bold statement of its mission to explore, explain and protect the natural world," said John Loomis, a principal of SWA Group, one of the architecture firms that designed the living roof.