September 1, 2008
Part 3: The Engineering
Weighing the needs of the Academy against the building’s dramatic expression—seven rolling, seismically secured hills—required the work of 320 engineers.
Sitting in a darkened conference room at Arup’s San Francisco office on Market Street, Peter Lassetter flips through a book of early engineering sketches for the California Academy of Sciences. Lassetter, a principal at the firm and the project director for engineering services of the building, pauses on a drawing from 2001, when the design was still very much in flux. Across the rough sketch is written an annotation in clear printed letters: “Crazy! Don’t do it!” That engineer’s plea may well have been heeded—Lassetter couldn’t quite make out from the drawing what was being warned against—but Arup certainly toyed with its share of crazy ideas while working on the Academy, which demanded a team of 320 people (drawn from its London, San Francisco, Sydney, and Hong Kong offices, among others) and included the structural, mechanical, and facade engineering; sustainability consulting; and lighting design. Many of those ideas, in fact, ended up forming the sustainable backbone of the Academy, the features that transformed it from a very green museum into a living, breathing one.
The breath of the museum is both literal and metaphorical: its lungs can be found in the contoured two-and-a-half-acre green roof (the Academy calls it a “living roof”) that is not only the building’s signature gesture, but also the key to its energy-efficient design. The two largest hills rise 27 feet above the roof line as they follow the outlines of the spherical planetarium and artificial rain forest below; the other five slopes weren’t designed with a programmatic purpose in mind. (According to the museum’s press department, they are meant to evoke San Francisco’s quasi-mythical seven hills. As an alternate explanation, Lassetter deadpans, “There’s no truth to the fact that Renzo’s from Italy and there are seven hills in Rome.”)
But Alistair Guthrie, a director of Arup and a mechanical engineer, devised a way to use the hilly topography to turn the roof into what Jean Rogers, a sustainability consultant at Arup, calls an “organ regulating the building’s metabolic processes.” A gap of four feet was left between the tops of the two spheres and the roof, creating what’s known as a stack effect: the narrowing space acts as a chimney, rapidly drawing out warm air through a series of skylights. At the same time, cool air enters the space through ground-level vents and doors, and a westerly breeze across the roof sucks more heat out. Computer-controlled actuators operate banks of 4,000 windows, opening and closing them as needed throughout the day. “As the building breathes, they will move,” Lassetter says.
The scheme ideally suits San Francisco, where high summer temperatures average in the 60s. Even with a glass facade, about 40 percent of the Academy is naturally ventilated, and 90 percent of regularly occupied spaces have daylight. “Museums are very, very highly conditioned spaces, both because of the loads of visitors, and also because of the collections that they’re trying to protect,” Rogers says. “So this idea of having a mixed mode of ventilation—collections that are protected but public spaces that are naturally ventilated and open and breathing, and in existence with the outside environment—it’s very, very unusual. Renzo was probably still thinking of it as a glass box with a green roof.”
The grand idea for the museum might have been settled on, but engineering a wildly rolling roof that could support 1.7 million plants in a half foot of water-saturated soil—and be porous enough to allow for light and air to pass through—was a long and difficult process. Just determining the number, size, and placement of the skylights above the rain-forest and coral-reef exhibitions took months of computer modeling. “People wanted to maximize the number of louvers in the sides of the skylights, but then there were structural engineers that didn’t want those big holes in the roof diaphragm,” Lassetter says. “And these spaces are all naturally ventilated, so we didn’t want lots of glass letting the sunlight in and, therefore, the solar gain upsetting it.”
One of the main challenges throughout the project was balancing green architecture with the needs of a research institution and museum whose collection of 20 million specimens demands strict regulation. Sometimes those goals were complementary. If you compare a glass of water from one of its fish tanks with a sample from a conventional aquarium, you’ll find a lot more stuff floating in the Academy’s. That’s because most aquariums want their tanks to be perfectly clear under the bright lights trained on them. For the Academy, Arup designed the lights to be more diffuse and farther away, allowing for much higher particle content in the water. “That saves a lot of energy on recirculating water because it doesn’t have to be kept gin clear,” Rogers says. “And it’s so much healthier for the fish—that’s what it’s all about.”
But elsewhere the profusion of artificial environments required elements—banks of metal-halide lamps cooking the coral reef, for example—that in a green building are like Texas oilmen crashing a Sierra Club meeting. Which is why it’s all the more impressive that the Academy stands to achieve a LEED Platinum rating. There is a litany of reasons why. All of the structural steel used in the museum is recycled; parts of the old building became a freeway in the East Bay. Sand excavated during construction restored nearby dunes. Fourteen miles of polyethylene piping run under the floors, giving the museum another means to regulate its environment and reducing energy use by as much as ten percent; a perimeter canopy of photovoltaic cells (which Piano actually wanted to be green in hue before Arup convinced him that a drabber color would be more efficient) provides at least five percent of the building’s power. And, while the natural ventilation in the exhibit hall makes it comfortable, Arup didn’t try to micromanage the temperature, relying on a bit of pop psychology to overcome modest fluctuations. “Because it’s such a transparent building, you’re always aware of what it’s like outside,” Lassetter says. “So people are actually a lot more forgiving—if it’s cold and nasty outside, they keep their pullover on, and they do it automatically. They can actually tolerate colder and warmer temperatures if they have that connection to the outdoors.”
Even the structural engineering reflected Arup’s holistic approach. Since earthquakes represent an existential threat to the institution—it has been effectively destroyed by them twice, first in 1906 and again in 1989—great care was taken to protect against the nearby San Andreas Fault. (One of the highlights of the old Academy was an earthquake-simulation exhibit, a raised platform that mimicked the queasy rolling of a major temblor, accompanied by scripted video of flimsy homes collapsing and a cook dropping a huge pot of boiling water. Sadly, it won’t reappear in the new building.) The four corner concrete structures—African Hall, two office-and-research buildings, and a pavilion holding the restaurant and gift shop—are independent buildings with shear walls that, in a big earthquake, will rock back and forth as much as three-quarters of an inch in their foundations.
The way the engineers kept the whole thing safely in one piece was by binding the four buildings with the roof. Each one acts as a sort of table leg to which the roof attaches as a tabletop. “It’s a great way of dissipating seismic forces, because to pick an entire building up takes a lot of energy,” Lassetter says. “If you hold it down rigidly, you’re using brute force to resist the earthquake.” There’s a neat resonance here with Arup’s sustainability work on the Academy: instead of letting the buildings succeed or fail on their own, the engineers hung them all together.
Making a building come alive is a tricky thing, especially in one with so many (actual) balls in the air. There is the danger of stitching together too many gadgets without giving enough thought to the whole. The roof somehow synthesizes the building’s green attributes almost effortlessly. “It could have ended up being a real Frankenstein,” Rogers says, “trying to do energy production and daylighting and natural ventilation and a green roof all in one—but when you’re up there, you’re like, It’s the way it should be. It just fits with the Academy’s program and the park, and yet if you had to sit down and design something that did all those things, it could be awful.”
Green Architecture’s Grand Experiment
