Greening The Mile-High City: A dramatic central atrium and a green roof elevate the profile of this federal office building
Designing the U.S. Environmental Protection Agency’s Region 8 Headquarters, in Denver, was complicated. The project’s most obvious puzzle was how to meet EPA’s space requirements on the tight, 1.3-acre site while following federal security protocols. The design couldn’t put any EPA space “within 50 feet of a potential blast force at the ground plane—in other words, a car,” says Peter van der Meulen, AIA, project manager at Zimmer Gunsul Frasca (ZGF) Architects, the project’s design architect. The simplest solution might have been to install bollards to prevent cars from getting too close to the building and then buffering the building with landscaping. In order to provide enough floor space, however, this strategy would have required a compact box in the middle of the site, which in turn would have threatened EPA’s desire for daylighting and the design-review board’s desire to maintain street frontage.
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Instead, the project team brought the building perimeter nearly to the property lines and installed retail space instead of EPA space wherever the blast zone extended into the building. This strategy bought enough room to allow for a glass-topped atrium in the middle of the 292,000-square-foot building, dramatically increasing the daylighting potential. The plan also allowed the building to maintain street frontage, reinforcing the warehouse aesthetic of Denver’s historic Lower Downtown, or LoDo, district. With intense oversight from LoDo’s design-review board, ZGF designed the nine-story project to look something like “an old brick four-story warehouse with a highly glazed tower rising out of it,” says John Breshears, AIA, project architect and environmental design coordinator for ZGF.
The next challenge was bringing daylight into the building while minimizing heat gain and glare. LoDo’s street grid is rotated about 45 degrees away from true north, an awkward orientation from an energy standpoint. The building uses the same type of double-paned, argon-filled, low-emissivity glazing on all its sides, but the facades handle shading in different ways. The southeast and southwest walls use horizontal exterior shades to block high-angle light; the northeast and northwest walls, however, which receive direct solar exposure only in the mornings and evenings, use vertical exterior shades to block low-angle light. This pattern is mirrored inside the building, with horizontal blinds and lightshelves on the south-facing walls and vertical blinds on the north-facing walls.
The team also worked to ensure effective daylighting from the building’s core. “We needed to bounce light into the atrium but also block direct sun—and consequently glare—from bothering people on the upper parts of the building,” says Breshears. The typical high-tech solutions—such as the sun-tracking mirrors used at the Genzyme Center in Cambridge, Massachusetts—were far too expensive. As the team explored options using a heliodon and an overcast sky box, van der Meulen, a sailor, hit on an innovative and decidedly low-tech idea. ZGF hired a Portland, Oregon, sailmaker to craft nine parabola-shaped sails supported by stainless-steel tubing. When the contractor balked at installing the sails, ZGF found a theatrical-rigging company to do it. The sails came in “substantially under the budget,” says Breshears. “They’ve gotten rave reviews.”
Although the security requirements prohibited operable windows, the team took advantage of free cooling through an air-side economizer. The team also installed a water-side economizer on a chilled-water plant. “When we only need a little cooling, we can pull directly from the cooling tower instead of the chillers,” explains mechanical engineer Rob Bolin, PE, of Syska Hennessy Group. Most of the building distributes heating, cooling, ventilation, and power through a 16-inch raised-floor plenum. The U.S. General Services Administration (GSA) has struggled with these systems in other federal buildings, but Syska has been investigating the problems for GSA. “We were able to learn those lessons,” says Bolin, who believes that careful attention to detailing and sealing will prevent similar problems in this system. The project also features a demand-controlled, heat-recovery ventilation system and an efficient lighting system controlled by occupancy and daylight sensors. By cost, the project was expected to use 35 percent less energy than a comparable building in minimal compliance with ASHRAE Standard 90.1-2004.
Perhaps the most important environmental strategy is the operational decision to schedule janitorial services during the day instead of the evening, allowing the Opus Corporation—the project’s owner, developer, and architect of record—to effectively put the building to sleep at night. “We turn off the lights and mechanical systems from 6 p.m. until 3 a.m.,” says Amy Smith, who works in the building as a property manager for Opus. The benefits are not only a striking drop in energy use but also a reduction in nighttime light pollution, the ability to clean spills soon after they occur, and a more convenient schedule for maintenance employees. In another operational innovation, Smith and her staff manually close the blinds on the building’s south elevations every Friday evening to block heat gain over the weekend and reduce the amount of cooling needed on Monday morning. “Saving energy doesn’t have to be rocket science,” says Smith.
The project’s water efficiency is also impressive, especially given Colorado’s unusual water-rights laws, which prohibit the collection and reuse of rainwater and even graywater. Low-flow faucets and showerheads, dual-flush toilets, and waterless urinals contribute to a 40 percent savings in potable water, compared with a similar conventional building. The waterless urinals required some negotiating with the city of Denver, which granted permission only after the team agreed to install plumbing to support conventional urinals if needed.
The project team also negotiated with the city to allow a green roof to substitute for the required stormwater storage and filtration system. The officials were hesitant but willing to give it a try if EPA would agree to monitor the roof’s performance and share the findings. The resulting 19,000-square-foot installation, made up of trays planted with sedums, is located on the building’s eight-story southern roof and shielded from winds by the nine-story portions to the north. The roof ran into some trouble the first year; trays in front of windows fared particularly badly: “The reflected sunlight burned the plants,” says Smith. Some rearranging, however, combined with more consistent irrigation, has solved the problems. While the team initially planned to use the irrigation only during a two-year startup period, Opus now believes the irrigation will have to be permanent.
Although the size and complexity of the project team were a challenge, “everyone was on the same page in trying to get as high-performance a building as possible,” says Bolin. They lost a few battles: Federal security protocols won out over operable windows, Colorado’s water-use laws won out over rainwater and graywater harvesting, and cost concerns won out over the building-integrated solar and wind systems included in early designs. The team prevailed on several green strategies, though, including the waterless urinals, green roof, and extensive daylighting. “It was a real team effort,” says Bolin, “and it was very rewarding.”
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