April 17, 2003

A building for Seattle's next 100 years

Photo courtesy of BA/BCJ Glass fins along the north face of City Hall are designed to catch light and reflect it into the building. Sensors read lighting levels inside and adjust lights to compensate.

One of the primary goals for the design of City Hall is to reflect and respect Seattle’s natural environment. This is achieved primarily through access to natural light and views, and a generous visual and physical relationship between the plaza and the building.

The new City Hall is built of stone, glass, metal and wood, and includes beautiful and accessible details that will delight users. Perhaps this quality — that people will enjoy being in this place — will be its most sustainable feature. The design is meant to endure 100 years, with systems that allow easy renovation to the building in areas that need to adapt to changing city services and changing technology.

The city identified the LEED silver rating as a sustainability goal, and the design is meeting this goal. Early in design, a sustainability charrette led by Arup identified a series of potential “green” strategies for mechanical systems, energy creation, building skin design and operations. Systems including double walls, photovoltaic glazing, water reclamation, under-floor HVAC, light shades and reflectors have been studied. Systems providing significant environmental benefit or good return on investment have been incorporated in the design.

Lighting

Seattle City Hall is designed to take advantage of natural daylight, decreasing the need for artificial light. Skylights and glass walls enhance public rooms, and daylight in the main lobby is controlled through wood louvers that add character and detail. Windows orient visitors to views and direction within the building, thus helping to decrease the need for lighting and signage.

The city street grid sits slightly askew to a true compass axis, providing unique opportunities to capture light within the building. The “north” face of the building is sheathed with glass curtain wall with vertical louvers. These louvers catch light and reflect it into the office space. Sun louvers on the “west” face work in concert with light shelves to protect workers from harsh daylight while reflecting light deep into adjacent office areas.

These light shelves reduce the need for artificial lighting in the perimeter areas, where photo sensors control efficient T5 indirect lighting fixtures via dimming ballasts. As daylight brightness increases, the lights respond by gradually dimming.

Building systems

Under-floor displacement ventilation allows the use of higher-temperature supply air at lower velocity, saving fan and chiller power. This raised-floor system also allows workers to adjust their space for personal comfort, unlike a more traditional overhead system. Studies show that individual control directly corresponds to a decrease in energy use. The raised-floor system also allows for easy renovation of office space, greatly reducing future energy consumed by altering the mechanical and electrical systems.

A thorough and detailed commissioning process for HVAC and electrical systems completed by an independent commissioning agent will enhance reliability and verify energy-saving equipment operation.

Water quality

The existing urban site has no water quality or flow control system. Runoff from the site goes directly into the city’s combined storm/sanitary system.

The rainwater harvesting system will collect and reclaim water for toilet flushing and site irrigation. The average annual rainfall is nearly in perfect balance with the building’s projected irrigation and flushing needs. This greatly reduces impacts on the city’s wastewater treatment plant, especially during storms.

A second water quality feature is the building’s garden roof. This planted roof system reduces heat absorption, increases water retention on site, decreases the load on the stormwater system, filters the water for better water quality, and provides a changing roofscape as the plants turn color with the seasons.

Alternative transportation is encouraged by proximity to transit lines and by bicycle storage and shower facilities.

Limiting waste

The construction waste plan resulted in recycling or reuse of over 75 percent (by weight) of construction waste and demolition debris.

Space is provided in the building for recycling bins in the trash collection areas. The city operates an aggressive recycling program including a commitment to “close the loop” by buying recycled products.

Recycled or reused materials

City Hall will include a number of recycled content materials including structural steel, concrete, carpet and carpet pad, low-density polyethylene toilet partitions, and recycled glass in the toilet room tile. Recycled-content gypsum board and ceiling panels are also being used.

Indoor air quality

A construction indoor air quality-management plan has been implemented by the contractor. A two-week building ventilation flush-out will ensure air quality. Permanent carbon dioxide monitoring systems provide feedback on space ventilation performance and allow for adjustments to maintain air quality.

Under-floor HVAC distribution includes over 90 percent of occupied spaces in directional airflow and provides individual control of air velocity and temperature in office areas. Low or zero volatile-organic-compound adhesives, sealants and paints are specified.

Permanent entryway systems capture particulates before entering the building. Copying, chemical storage, and housekeeping areas have separate direct venting and negative air pressure to ensure these areas will not contaminate the air in the rest of the building.

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