Photo © Bruce Damonte
Public Utilities Commission
Reframing Sustainability: An unusual seismic system ties together an office building’s green strategies.
By Joann Gonchar, AIA
Part of the north face of 525 Golden Gate Avenue is a kinetic canvas. Its surface, a permanent installation by environmental artist Ned Kahn, is made up of thousands of hinged polycarbonate panels that ripple in the wind. And at night, the wind gusts trigger the flickering of tiny LEDs embedded in its fish-scale-like tiles. Kahn’s undulating veil makes the power of natural phenomena legible in a way that is similar to the four vertical-axis wind turbines stacked behind it. Although the turbines are expected to generate only 4.9 kilowatts, or about 1 percent of the 277,500-square-foot building’s power demand, their spinning serves an important purpose. It announces the green goals of the LEED Platinum–aspiring project, which is the new, $146.5 million headquarters of the San Francisco Public Utilities Commission (PUC). The agency provides wastewater treatment to the city, potable water to much of the Bay Area, and hydroelectric power to municipal facilities.
Location San Francisco Peninsula
Gross area 277,500 ft2 (258 m2)
Cost $146.5 million
Completed June 2012
Annual purchased energy (based on simulation) 48 kBtu/ft2 (540 MJ/m2), 24% reduction from base case
Annual carbon footprint (predicted) 9.6 lbs CO2/ft2 (47 kg CO2/m2)
TEAM & SOURCES
Interior shades MechoSystems automated roller blinds with EcoVeil and midnight blackout shades
Wood-slat ceiling panels 9Wood
Acoustical-ceiling system Hunter Douglas Techstyle E
The sleek, 13-story glass box, designed by a joint venture of two local firms—KMD Architects and Stevens + Associates—incorporates a host of other resource-conserving features predicted to save almost a third of the energy and 60 percent of the water consumed by a typical office building. Except for two vertical swaths of sierra white granite intended as a nod to the buildings of the nearby Civic Center, the PUC is wrapped in a double-glazed, high-performance curtain wall with operable windows. It has interior and exterior shading devices for controlling glare and minimizing heat gain, light shelves for daylight harvesting, an under-floor air-distribution system, and a 164kW roof-mounted photovoltaic array. The lobby and the building’s sidewalk house a “living machine”—a gray- and blackwater-reclamation system that looks much like ornamental, gravel-filled planter boxes.
The least obvious green feature, but one that ties all the bells and whistles together, is the poured-in-place concrete structure. It is made of several mixes that, in total, replace about 70 percent of the portland cement normally in concrete with slag and fly ash (byproducts of steelmaking and of coal-fired energy generation, respectively). The result is a frame with a carbon footprint about half the size of that associated with a typical concrete structure, according to Berkeley-based Tipping Mar, the project’s seismic consultant.
The structural system includes two vertically post-tensioned cores designed to provide a restoring force during an earthquake, closing cracks as they develop, explains David Mar, principal at Tipping Mar. This so-called self-healing capability should prevent 525 Golden Gate from sustaining damage and keep it safe for employees to occupy after a significant seismic event. The approach goes well beyond code requirements, which emphasize preventing loss of life rather than minimizing property damage or limiting interruption to business operations. This added durability is closely tied to the client’s view of sustainability. “The idea was to construct a resilient building,” says Brook Mebrahtu, senior project manager for the San Francisco Department of Public Works.
The decision to make 525 Golden Gate’s structure concrete was made after completion of design development. Earlier plans called for a steel frame with almost the same seismic performance. The switch was part of an aggressive cost-cutting exercise that shaved about $10 million from the budget and permitted the insertion of an additional floor in the same zoning envelope. About half of the savings can be attributed to the elimination of elements associated with the steel scheme, such as fireproofing, and the choice to leave much of the cast-in-place structure exposed, which in turn allowed the elimination of suspended ceilings.
The client was somewhat resistant to the aesthetic of exposed concrete—at least at first—but the savings were hard to ignore. And there were synergistic advantages that supported the project’s green ambitions. For example, the approach allowed a reduction in finishes, and a corresponding reduction in embodied energy, even though ceiling “clouds” were needed to improve acoustics in the largely open offices. “We were able to strip away layers of normally required materials,” says Jill Kuper, an associate at Tom Elliot Fisch, the San Francisco firm responsible for the PUC’s interiors
One of the most notable benefits of the decision to leave the concrete exposed was an improvement to the building’s daylighting scheme. Because the new concrete structure made spandrel beams unnecessary, designers were able to taper the underside of floor slabs toward the curtain wall to help bounce the sun’s rays from light shelves to the concrete surfaces, and deep into the office floors. Photo cells control the work areas’ indirect lighting, dimming fixtures when daylight levels are sufficient.
This illumination strategy—which Michael Rossetto, KMD’s project architect, calls “passive lighting design”—required a surprising level of cross-disciplinary interaction. To make sure the tactic worked, lighting designers asked the structural engineers to include a minimum reflectance value in the concrete specifications—a highly unusual request for poured-in-place construction. “We had many consultants talking to each other that normally wouldn’t need to,” says Rossetto.
The connection between the daylighting scheme and the concrete demonstrates that 525 Golden Gate is more than a collection of the latest green gadgets. Instead, it’s almost like an organism, made up of mutually dependent, and finely tuned, elements.