Precast concrete helps a major firm’s new world headquarters meet multiple goals of environmental sustainability, decreased cost and long-term flexibility.
By Deborah R. Huso
When CH2M HILL, a leading international engineering firm, set out to build a new corporate headquarters, Leadership in Energy and Environmental Design (LEED) certification was a goal right from the start. CH2M HILL wanted a headquarters campus that met three important goals: environmentally sustainable design, ease and speed of construction and flexibility for the future.
When project architect Michael Barber of Barber Architecture in Denver came on board at the start of the CH2M HILL headquarters planning process, precast was not his only consideration for the campus buildings’ design.
“In the early stages, we considered steel, cast in place and precast,” Barber says. Ultimately, the design team chose precast. Barber says the reduced cost was the biggest deciding factor, but the sustainability features and ease of installation were also considerations. Barber has become a leading proponent of total precast concrete structures over the years, appreciating the inherent advantages offered when structure and architectural detail can be melded into one component.
MEETING LEED STANDARDS THROUGH PRECAST
“LEED was a goal from the beginning,” Barber notes. “We took several field trips to leading-edge sustainable buildings all over the country and in Canada.” When the design team settled down to work, meeting points for LEED certification was central. The team started out planning only two buildings, but over time, the campus project developed into four structures, all of them similar in design, all of them made from precast wall systems that would serve as both structural and architectural panels.
“LEED was just starting up at the time of the first building,” says Dan Parker with Rocky Mountain Prestress, the project’s precast manufacturer. The use of precast concrete became central to the design team’s efforts to obtain points for LEED certification. In fact, the four buildings’ total precast structural systems represented the most important component of the campus’ sustainability goals, particularly in the areas of using recycled content and locally sourced materials. Cement can make extensive use of recycled materials. For example, the precast wall panels used in the CH2M HILL buildings were formed using concrete made, in part, from fly ash (a recovered byproduct of coal-burning plants) of which some 750,000 pounds were used. The rebar used in the concrete was also nearly 90 percent recycled content, having been made from scrap steel.
The portland cement used in the buildings was acquired from sources in the Denver area, thus minimizing the transportation costs and environmental impacts often associated with construction projects that make use of materials from distant locations. “The sand, aggregate, cement — everything was from Colorado,” Parker says.
The precasting facility is located only 20 miles from the construction site. Nearly 60 percent of the CH2M HILL campus’ construction materials came from local sources. The buildings’ precast materials accounted for almost 40 percent of those locally acquired building materials.
Another advantage of precast concrete was just-in-time delivery of the precast. The wall panels arrived on site ready to install, limiting the construction waste from pouring concrete on site or erecting a steel frame. And, in the instance of the CH2M HILL buildings, wall panels served as both structure and facade, further reducing material usage. CH2M HILL’s buildings feature a 50-foot-long bay on each end as well as 20-foot-long bays at the center of each structure. And the architectural precast panels are load-bearing, supporting double tees for flooring.
Furthermore, precast wall panels require minimal maintenance and have a long lifespan, leading to less money, time and materials spent in the upkeep of the buildings. “There’s no need for staging on site,” Parker notes. “Precast shows up on a truck and is put up piece by piece.”
The four CH2M HILL buildings all benefit from the inherent properties of precast, including the higher energy performance of concrete. Concrete’s high thermal mass and low temperature transfer and air infiltration make it naturally energy efficient. The result is that HVAC systems don’t have to work as hard to heat and cool.
PRECAST OFFERS FLEXIBILITY
Sustainability concerns were not the only factor in choosing precast for the CH2M HILL buildings. “The client also wanted a site with flexibility,” Barber explains. “They wanted the site to offer opportunities for expansion.” CH2M HILL envisioned leasing one or more of the buildings to tenants in the future and wanted structures that would suit the needs of
various industries, rather than reflecting the exclusive personality of one company.
“This project was meant to be market conforming,” Barber says. “If CH2M HILL ever moved its headquarters, this campus would be attractive to other tenants. The buildings were not designed to be unique.” Furthermore, in the current climate of sustainability awareness, it’s no small thing to be able to offer potential future tenants and owners LEED-certified structures.
“The result is that these buildings are totally flexible,” Barber says, noting that while they are attractive, their design is relatively simple, allowing for a variety of uses. The simple design also decreased construction time. “We were able to erect the buildings faster and, thus, do the interiors faster,” Barber notes, explaining that quick occupancy was a major goal. Roger Eastman, project superintendent for The Weitz Co., which was the CH2M HILL campus general contractor, says it took only about 12 weeks to put up one four-story building of about 120,000 square feet. “And a building could get to roof level in only eight weeks,” he adds. That was after about six weeks of construction time per building in the factory. Altogether, the four CH2M Hill buildings total about 467,000 square feet.
The structures’ simple design also contributed to project speed and lower cost. “With precast, it’s good to have as much repetition as possible, so you build fewer forms at the factory,” Barber explains. He says the CH2M HILL buildings take advantage of the inherent cost saving advantages of precast concrete by making use of large panels (the biggest ones are 15 feet by 30 feet and weigh up to 60,000 pounds) and minimizing the number of different molds. With the exception of deep reliefs to create a shadow effect on the buildings’ facades and the use of two different color mixes in the concrete as well as acid-etch finishing to set off building entrances, there is very little variation in the wall panels that serve both as exterior surface and as the beams holding up the structure.
Eastman agrees that repetition is key, noting that with the CH2M Hill project all the buildings were basically simple rectangles. “It was the smoothest-running project I ever built,” he says. “We were able to put up a project in no time flat, and precast allowed us to have a homogenous look to the buildings in a short timeframe.”
“When you design with precast, it has inherent advantages,” says Barber. “You don’t have to have a craftsman cutting stone to get architectural detail. It’s all done in a mold in the factory.”
“It’s a one-stop shop for the general contractor,” Eastman adds. “You get the structure and architectural product in a one-trade effort.”
Deborah Huso is a freelance writer who covers home design and restoration, sustainable building and design, and home construction.
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