Chicago Parks District Field House Prototype 1
While OSB SIPs currently dominate the commercial and residential markets, precast-concrete SIPs, which were first produced in the 1960s, are making headway in the industry. Though they employ the same insulating material—typically EPS—as their OSB counterparts, precast SIPs can be used architecturally as well as structurally. They also offer a durability ideal for high-traffic projects, such as public facilities and schools.
“It carries loads, creates a good durable finish, doesn’t burn or mold, and the insulation gives you high R-values,” says Brian Miller, managing director of business development at the Precast/Prestressed Concrete Institute (PCI), an industry organization based in Chicago. Precast SIPs also possess thermal mass, he says, allowing them to absorb and release energy slowly. While offering R-values similar to those of OSB SIPs, the precast panels’ combination of thermal mass and insulation creates a high-performance wall system that can create up to 25 percent savings on heating and cooling costs, according to PCI.
Chicago-based architecture firm Booth Hansen chose precast concrete SIPs for its design of a field-house prototype for the Chicago Parks District, which mandated that the project achieve LEED Silver certification. The 18,000-square-foot facility—designed with the potential to expand another 12,000 square feet—contains administrative and support functions, a gymnasium, and several fitness rooms.
One challenge that the designers faced in using precast SIPs for this project was the looming wall heights—up to 31 feet in the gymnasium. In order to provide adequate structural support within the panels to manage the walls’ dead loads, the SIPs were fabricated with concrete-composite ribs that tie together the exterior and interior concrete wythes. Because concrete is a poor thermal conductor, the risk of thermal bridging due to the connectors is not significant.
On the other hand, using precast SIPs allowed for fast erection times—even faster than those possible with conventional OSB SIPs; not only can the structure’s precast envelope and insulation be installed in one fell swoop, but precast SIPs can also be prefabricated with interior and exterior wall finishes already applied. The concrete can be molded to resemble brick, wood grain, or nearly any texture the designer can imagine. It can also be embedded with finishes such as brick veneer.
At the Field House Prototype 1, the exterior finish of the precast SIPs is exposed concrete with aggregate; form liners created articulated shadow lines, adding texture and a sense of permanence that is appropriate to a civic building. The finished interior wall, also exposed concrete, provides durability and eliminates the need for painting.
Saving Energy and the Environment
Structural insulated panels offer yet another instrument in a designer’s toolkit to create high-performance, economically efficient, and environmentally sensitive buildings. Along with creating tighter envelopes than are possible with traditional stick framing, SIPs combine the reliability of an engineered product complete with the waste-reducing benefits of prefabrication.
With the proper coordination and experience among the design and construction teams, SIPs can also lead to significant time savings on site and become a source of long-term energy savings—no small feat for today’s budget- and eco-conscious clients.
Note: This article and slideshow have been updated since first publication to reflect that the bulk of Finn Hill Middle School's construction was completed in about a year, and that the school is currently undergoing commissioning to ascertain whether it is meeting its targeted energy performance goals.