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October 31, 2002

A model for sustainable design

  • Green features abound at the Justice Center
  • By DUNCAN THIEME
    NBBJ

    layered curtain wall
    Courtesy of NBBJ/Steve Keating
    The model of the Justice Center’s west facade shows the layered curtain wall that composes the building’s thermal buffer. Two planes of glass set 30 inches apart form a naturally vented “double skin” that allows light to penetrate, but minimizes heat gain.

    As part of an effort to promote responsible stewardship of increasingly scarce natural resources, the city of Seattle mandated that the new Civic Center campus stand as a model for sustainable building design.

    The aim is to establish a sound environmental policy to which other organizations can aspire. In particular, the vision focuses on the design, construction and operation of new and existing public buildings.

    Sustainability goals

    In 1999 the project’s principal designers and engineers, as well as the management team, met to discuss the city’s sustainability goals for the Civic Center. The charrette focused on determining the elements required to signify a sustainable building, and developing strategies to achieve them. By day’s end, three goals were identified:

    • Achieve at least a silver rating using the LEED green building rating system

    • Make the sustainable features of the projects legible to the users and public

    • Set an example for good building practices that others can follow

    With these goals in view, the Seattle Justice Center team initially had to confront the fact that green buildings often involve more upfront expense, but demonstrate economy over their life cycles. As the budget for the Justice Center concentrated on construction costs, and as the funds available for greening features were limited, NBBJ restated the goals in terms that clarified implicit priorities:

    • Pursue any design features that help to achieve a minimum LEED silver rating

    • Emphasize those features that will be legible to people using the building

    • Pursue other ideas that have value as demonstration projects, but don’t further a high LEED rating

    LEED rating system

    Sustainable design for the Justice Center rests on the LEED green building rating system. LEED, or Leadership in Energy and Environmental Design, was developed as a way to define and prioritize green building strategies, and as an impartial method to evaluate the overall sustainability of a project.

    The system identifies five basic categories that correspond to general greening goals, each with an associated set of specific performance goals. Points are awarded for meeting each of these performance goals. The sum of all the points earned determines an overall score and rating for the building, which, in ascending order, are: LEED certified, silver, gold and platinum.

    Sustainable features

    Much of the effort that goes into the greening of a building is devoted to a series of thoughtful but small decisions. Characteristically, this means specifying equipment that is more energy-efficient than typical or looking for recycled alternatives to new building materials. Sometimes bigger steps are taken that have a more noticeable effect. For the Justice Center, a number of larger design decisions dramatically influenced the sustainability of the building. A brief description of each follows:

    Glazed thermal buffer

    Backed against an eight-story garage to the east, and facing high-rises on the north, the site for the Justice Center does not lend itself to large areas of glazing. Only the south and west sides of the building offer good exposure to natural light, which, from an energy standpoint, is the least desirable orientation.

    To counteract this dilemma, a large section of the building’s west facade was designed to have a naturally vented “double skin” glazed thermal buffer — a type of window wall that allows maximum penetration of light to the interior work spaces while minimizing heat gain.

    The façade is composed of two planes of glass separated by a 30-inch air space. Louvers inside the space, at the top and bottom, are on automatic control and can either be closed to retain air and create an insulating barrier on cold days, or opened to vent heat from assembly rooms on hot days. In the open position, air drawn into the cavity at the bottom of the wall rises as it is heated then ultimately vents out at the top of the wall.

    Systems like this have been in use in Europe for some time and have proven highly effective in reducing energy consumption while maintaining a high level of transparency. In the Justice Center, the design makes sure that the large public lobbies and major areas of open office space face the curtain wall. This maximizes exposure to natural light for as many of the building’s occupants as possible, both enhancing the quality of the spaces and reducing the energy spent to light them.

    Finally, in order to throw natural light as deeply into the open areas as possible, a light shelf was incorporated into the design of the curtain wall at each floor. The shelf, located eight feet above the floor, projects horizontally into the space to shade unwanted glare, reflect sunlight onto the ceiling, and diffuse light throughout the space.

    Planted roof

    The principal roof areas of the building are designed as a “green” roof. A layer of soil is spread over the top of a membrane roof in which grasses and other plants grow. This design has several environmentally valuable consequences.

    It provides insulation, both by adding a layer of soil and removing solar energy through photosynthesis; it absorbs and stores rain water that might otherwise find its way into the sewers; and it provides a large green space that filters pollutants out of the air while returning some oxygen to the atmosphere.

    The planted roof is next to the public outdoor terrace on twelfth floor to give visitors and staff a pleasant outdoor landscape.

    Water harvesting

    A water harvesting system collects rainwater that falls on the site and stores it for later reuse. This will reduce the building’s consumption of municipal potable water to irrigate plants or charge the water feature in the public plaza.

    Reaching goals

    The Seattle Justice Center is on track to reach the challenging sustainability goals posed by the entire Civic Center project. A careful analysis shows that the building is designed to achieve a LEED silver rating while the use of innovative technology, based on proven results, sets an example of responsible building development for others to follow.


    Duncan Thieme is a LEED-accredited professional at NBBJ.


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