A model of sustainable design with energy-efficient precast concrete wall panels and green roofs, the $12.5-million, LEED Gold-certified Engineering Building is currently under construction for the Metropolitan Sewer District of Greater Cincinnati.
By Sue McCraven – Photos courtesy of High Concrete LLC
Bidding against stiff competition from local design/build firms, Cintech and KZF Design won the award to construct a 59,000-square-foot municipal structure, a project planned from the outset to earn a LEED (Leadership in Energy & Environmental Design) Silver Certification. Based in Cincinnati, KZF Design and Cintech Construction were commissioned to design and build a three-story glass, steel and precast concrete facility for the Metropolitan Sewer District of Greater Cincinnati (MSDGC) wastewater engineering staff. High Concrete Group LLC of Springboro, Ohio, the precast concrete producer, fabricated insulated, high energy-efficient wall panels for the structure. In this article, project principals from KZF and High Concrete share their experiences and advice for planning and constructing the facility, which moved up from LEED Silver to LEED Gold during the design/build process.
DETAILS ON LEED CREDIT ELEMENTS
Vegetative roof reduces stormwater runoff: MSDGC’s wastewater engineering building is designed with vegetated roofs to optimize energy performance and reduce stormwater runoff to help meet LEED certification prerequisites. A modular design, the 4-inch-thick extensive-type vegetative roof system uses a fully adhered 72-mil-thick white TPO (thermoplastic polyolefin) membrane with heat-welded seams.
The TPO system comes with a 20-year manufacturer’s system warranty that covers watertightness and removal of the overburden (vegetative modules) as needed for repairs.
According to KZF project principals, the vegetative roof weighs 22 pounds per square foot, a significant increase over a traditional roof loading of about 12 pounds per square foot. Heavier roof loading required an increase in the carrying capacity of the underlying steel support structure and the concrete pier foundations.
Solar control: Glass selection is a crucial factor in balancing energy performance, occupant comfort, maximization of natural light and the reduction of greenhouse gas emissions. To achieve this balance, clear 1-inch-thick insulating glass units have MSVD1 low-E2 coatings that reduce solar heat gain, provide high visible light transmittance and are neutrally reflective with a spectrally selective light-to-solar gain ratio of 1.84. To further reduce solar gain during the cooling season, projected sunshades have been added along the south and west portions of the building.
Thermally improved curtain wall: A standard, thermally improved, aluminum-framed curtain wall system with a Class I clear anodized finish is employed.
Energy-efficient precast wall panels: Precast concrete was selected over competing materials because precast offers long-term durability, as well as manufactured cost savings and quality control. With its inherent thermal mass and additional insulation, the panels provide high energy efficiency for occupant comfort. Specially designed architectural precast panel finishes were fabricated with brick inserts to blend with the existing municipal campus in addition to providing a high insulation rating.
Reinforcing steel used in precast panels is a recycled product that qualifies for LEED credits. In addition to the thermal advantages and recycled materials used in precast concrete as a single-component solution, precast also earns important LEED points for source quality control, use of regional materials and production facility, and employment of local labor. Precast concrete’s consistent quality and many inherent green advantages proved to be a winning strategy for the KZF/Cintech Design team. The design/build team was able to reduce project costs with precast production savings when the owners moved up from LEED Silver to LEED Gold certification.
Educational opportunities in sustainable design: Educational opportunities at this new MSDGC facility are designed for middle school, high school and college students (as well as corporations) who wish to learn more about effective wastewater treatment processes and sustainable designs to protect the environment. In mind of future educational and corporate programs, at the entry of the new engineering building, a flowing, colored water feature will represent the liquid stream wastewater treatment process (see related article, “What it Takes to Produce a Design/Build LEED Gold Project”).
CHALLENGES OF LEED PROJECT WORK
Rick Lorenz, a precaster with 40 years of experience in the industry and project manager at High Concrete Group, says there is one major challenge that will set a LEED project apart from any other work a precaster will ever do. “The amount of paperwork involved in a LEED-certified project is significant,” he says. While Lorenz further describes the record-keeping required in slightly more colorful language, it is sufficient to note that the accounting required for LEED credits may be quite time-consuming.
In addition, Lorenz explains that separating out the exact amount of recycled steel used for a particular LEED project from the tonnage ordered for all precast plant jobs can be challenging.
“We buy (rebar) in quantity as most fabricators do, to capture the cost benefits of mass purchasing,” Lorenz says. “Breaking out the precise weight of recycled rebar used in the MSD project was a tedious task.” On the plus side, the recycled steel bar itself is an important component in sustainable construction.
“One of the two main reasons that precast concrete products are well-suited to sustainable LEED certified work is that all the reinforcing steel used is recycled material,” Lorenz adds. Recycled materials help achieve LEED credits. The second significant advantage that precast concrete offers in fulfilling green construction requirements is that the materials are typically manufactured within 500 miles of the job site, saving on transportation costs and — importantly in today’s economic condition — using regional materials and local workers.
Portions of the exterior walls are clad with half inch thick “thin brick,”over insulated architectural precast concrete.
“Using thin brick in the custom-made forms created project savings, both cost and construction schedule, when compared with field-constructed masonry work,” Lorenz says (see production photos, Fig. 1 to 3). The brick inserts and precast wall panels were fabricated in mock-ups designed to duplicate the architectural style and color of adjacent MSDGC buildings. The precise look the architect envisioned in the finished brick detailing proved to be a challenging issue for the precaster.
As most designers and manufacturers know, the devil is in the details.
“The hardest thing, really, on this job was developing the exact contrasting brick colors that the owner and project architect wanted,” Lorenz says. “We had two different colors of brick and two different mortar colors to integrate perfectly into the panels, with no bleeding of the red mortar into the buff color, or visa-versa. We used form edges, or reveals, when placing the colored mixes for the surface depth of the forms. But even with the care that went into creating the exact colors and finish desired by the owner, the
precast production efficiencies saved project costs over a true brick veneer on the building.”
Sue McCraven, NPCA Senior technical consultant, is a civil engineer, technical writer and editor, and environmental scientist who has contributed numerous articles and studies to prominent scientific journals.
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