Adjacent to the Seattle Center and its towering Space Needle, a sprawling asphalt parking lot covered fertile ground that once had a rich history. The 12-acre site had been a clearing in a forest with a wetland that provided respite for migratory waterfowl traveling the Pacific Flyway; it had also been a meadow where Native Americans held community potlatch ceremonies. Over the years, the site was built up to house, at different times, railway trestles, homesteads, farming, a street-car barn, and a bus barn.
In spring of 2011, the urban plot became home to the new Bill & Melinda Gates Foundation campus, which incorporates natural and structured elements to attract wildlife and support the foundation’s mission to help people lead healthy, productive lives. Parking structures support two acres of vegetated roofs that help return 40 percent of the 900,000-square-foot campus to green space with bird-friendly habitats and edible plants such as blueberries, huckleberries, and red flowering currant. A large central courtyard beckons geese and herons with textured paving and native plantings anchored by a reflective pond.
“The habitat restoration is one of the project’s most wonderful aspects,” says Margaret Montgomery, AIA, principal and lead sustainable designer at NBBJ, the Seattle-based architecture firm for the project. “Almost immediately, the site became a stopping place for migrating birds between Lake Union and Elliot Bay. It’s very urban, but it allows humans and nature to cohabitate.”
The office wings accommodate up to 750 people each, with three buildings spreading across nearly 640,000 square feet of occupied space. Floor plates that are 65 feet wide position all employees within 30 feet of incoming daylight, and 10-foot-high curtainwalls leverage outdoor views. The offices also welcome visitors and grant recipients throughout the year.
The Gates Foundation wanted to address its larger environmental footprint. “We grounded our sustainability strategies in what was right for the project, then back-checked our goals against the LEED rating system,” Montgomery says. “When we discovered we were very close to LEED Platinum certification, we pushed ourselves just a bit further to document what we had done.” The effort paid off: The project is the world’s largest nonprofit LEED-NC Platinum building and the second-largest LEED-NC Platinum building in the United States.
Protecting the Puget Sound watershed was also a high priority. The site’s former parking lot discharged 11 million gallons of polluted rainwater into the watershed every year. A combination of efficient plumbing fixtures and rainwater collection and reuse strategies completely eliminates all polluted rainwater runoff and reduces the building’s potable water use by 79 percent compared to the Energy Policy Act of 1992.
Two underground parking garages (one for the Seattle Center and one for the foundation) have expansive vegetated roofs covered in sedum that absorbs rainwater runoff and blooms at different times of the year to provide swaths of color for onlooking building occupants. A 1-million-gallon rainwater storage tank fills in approximately 11,000 square feet of unused space on one level of underground parking. The tank collects and filters runoff from nonvegetated roof and hardscape areas for use in irrigation, reflecting pools, and toilets.
Because cooling towers require tremendous amounts of water, the project team found another way to cool the buildings. A second underground tank, 60 feet tall and 50 feet in diameter, holds 750,000 gallons of water for thermal-energy storage. At night, plate-frame heat exchangers push chilled water pipes into the tank to bank it for daytime use. When the buildings are occupied, the heat exchanger pulls the chilled water from the tank and transfers it to the air-handling units to circulate cool air. Cooler nighttime temperatures allow the units to operate at lower pressures so they use less energy than during hot days.
Hydronic radiant heating is embedded in the concrete floor slab of the campus’s four-story atrium, where operable windows provide cooling and ventilation. The remaining occupied spaces rely on an underfloor air-distribution system that draws water from the chilled-water tank and heat from a gas-fired condensing boiler plant. Montgomery says that underfloor air can be delivered at a lower velocity and a slightly higher temperature since it enters the space at the floor level. “This allows us to take advantage of free cooling and save energy. The strategy also provides high indoor air quality because the air doesn’t have to mix in order to deliver ventilation or thermal comfort heat or cooling where it’s needed. It rises gently through the space and gets exhausted at the ceiling.”
On top of the wing housing the cafeteria’s kitchen and campus shower rooms, the team placed 47 evacuated-tube solar-hot-water collectors so that solar-heated water can flow directly to the sources without conversion. The system reduces natural-gas consumption for heating water by 4,750 therms annually and provides energy for approximately 36 percent of the domestic hot-water use.
Combined, the multiple energy-saving strategies lowered energy consumption by 39 percent compared to the ASHRAE 90.1-2004 baseline. The foundation will recoup its investment in energy- and water-related systems in less than 30 years.
“Creating a 100-year building gave us the ability to look at a longer-term payback and do some forward thinking,” Montgomery explains. “The underfloor air-ventilation system simplifies future space modifications, and we designed the roofs to accommodate photovoltaic panels when future technology makes them more financially feasible in Seattle’s climate.”
ECO-STRUCTURE contributing editor KJ Fields writes about sustainability from Portland, Ore.