Jury: “It is a project that established extremely high goals from the beginning. It is rare that you determine a desire to be a replicable model for other government buildings and this has followed through on that mission including very significant monitoring as evidence and an example for other buildings to follow.”

Architect: “With a net-zero goal, generating on-site renewable energy makes sense only after you’ve diminished the energy you need in the first place. … We used a mix of innovative new and off-the-shelf strategies to maximize performance across the board and then looked at how to elevate it to a higher level of architectural expression.” —Carey Nagle, AIA, lead designer and project architect, BNIM

As it is home to two state agencies that govern utilities issues, the Iowa Utilities Board Office of Consumer Advocate Office Building’s core goal was energy-related: to reduce its energy use intensity (EUI) to 28 kBtu per square foot per year, a 60 percent reduction from baseline energy code (defined by ASHRAE Standard 90.1-2004). To meet this goal, BNIM combined optimal orientation with massing and a hyper-efficient envelope. An envelope of white Thermomass precast concrete with continuous insulation and non-thermally-conductive ties eliminates traditional thermal bridging and helps modulate temperatures and reduce loads via the thermal mass of the shell. Other energy-related elements include a geothermal field that is tied to dual-stage heat pumps, a total-energy recovery unit, a roof-mounted 45-kilowatt PV array, low-power-density lighting, automated dimmers and occupancy sensors, and a comprehensive measurement and verification plan to measure all building-system energy use. As an example of this last component, the building’s automation system monitors conditions and emails occupants when windows can be opened or should be closed. In addition, the system automatically shuts down zone heat pumps when windows are open to reduce energy loss, and all outlets are tied to occupancy sensors that shut down non-critical loads when not in use.

The structure is split into two wings connected by a central lobby, with the State Utilities Board housed in two stories on the north wing and the state’s Consumer Advocate Office on two levels of the south wing. Each wing has an open plan configuration and modular workplace design to provide long-term flexibility. The open plan was also chosen based on daylight modeling, which demonstrated significant performance increases with the implementation of low furniture panels. The narrow north-south building configuration provides controlled daylight, and the east and west elevations are designed to mitigate excessive heat gain and glare. Louvered sunscreens on the south elevations reflect daylight indoors year-round and block summer heat, and Solatube skylights help bring light into the core.

Located in an area that is prone to flooding, the building is designed to capture and infiltrate all stormwater from the average annual rainfall event, and stormwater from six acres of adjacent streets is also diverted on-site treatment. The southern half of the site has a native prairie restoration and treatment train (consisting of a stormwater interceptor, infiltration basin, rain gardens, bioswales, and pervious pavement) to capture and filter stormwater. This element also eliminates the need for irrigation.

Building gross floor area: 44,640 square feet
Estimated percent of occupants using public transit, cycling, or walking: 22
Percent of daylight at levels that allow lights to be off during daylight hours: 98
Percent of views to the outdoors: 98
Percent of spaces within 15 feet of an operable window: 53
Percent reduction of regulated potable water: 46
Is potable water used for irrigation: No
Percent of rainwater from maximum anticipated 24-hour, two-year storm event that can be managed onsite: 36
Total EUI (kBtu per square foot per year): 22
Net EUI (kBtu per square foot per year): 20
Percent reduction from national average EUI for building type: 49
Lighting power density (watts per square foot): 0.75
LEED rating: Registered, LEED v2.2
Total project cost at time of completion, land excluded: $10 million

Data and project information provided by architecture firm via AIA COTE Top Ten entry documents.

For an extended view into BNIM's philsophies on sustainable design as well as a showcase of the firm's other green projects, click here. For more information on each project, as well as a database of past Top Ten projects, visit aiatopten.org.