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Geofoam SIPs: Thinking outside the (stick-framed) box

Case Studies | October 1, 2014 | By:


In this decade of emerging technologies that seek to decrease carbon footprints, structural insulated panels (SIPs) have come of age. More architects and builders are thinking outside the box when designing with SIPs-creating beautiful buildings that approach net zero energy use and offering some surprising extras-while incorporating aesthetically pleasing design elements. SIPs have been employed creatively to achieve multiple benefits for the owners and occupants.

Solar Decathlon awards

R-control SIPs (structural insulated panels) consist of expanded polystyrene (EPS) geofoam insulation laminated to oriented strand board (OSB) forming a structural panel. SIPs are used in walls, roofs, and flooring applications.

Start.Home, built with SIPs by Stanford University students, won first place in affordability and third place for market appeal at the U.S. Department of Energy’s (DOE) 2013 Solar Decathlon, held in Orange County, Calif., in October 2013.

The SIPs were incorporated in Start.Home’s floors, walls, and roof. According to Stanford’s Start.Home team project manager, Rob Best, r-control SIPs were instrumental in the team’s construction schedule and transportation procedures, bringing the home’s total estimated construction cost to less than $250,000, winning 100 points in the affordability contest.

“The Start.Home was designed from the start to be both technologically advanced and affordable,” said Best. “Through great design and engineering we were able to maintain the cost of our net-zero home at $235,000, remaining affordable in many parts of the country.”

The Solar Decathlon began in 2002 as a U.S. competition and has since expanded to a global competition hosted by the DOE to promote solar technology. This year, 20 competing teams selected by the DOE designed 1,000-square-foot homes for the Decathlon that were evaluated on 10 criteria: architecture, market appeal, engineering, communications, affordability, comfort zone, hot water, appliances, home entertainment, and energy balance.

Construction advantages

By design, SIPs arrived on-site cut to size and ready to go, which makes the construction process faster. The construction team was able to put together all of the walls of the Start.Home in three days. The house’s design structure also saves time and money for the owner, reduces the environmental impact of the construction process, and results in lower resource consumption.

Structural insulated panels (SIPs) are prefabricated structural elements used to build walls, ceilings, floors, and roofs. Made of geofoam insulation sandwiched between two layers of structural board, SIPs provide a more airtight dwelling than a standard stud-frame house. This also creates a quieter and more energy-efficient interior space.

R-control SIPs are two sheets of oriented strand board with expanded polystyrene (EPS) geofoam in-between. Building an SIP house differs from traditional “stick frame” construction because there are no studs in the walls, which means there is continuous insulation within the walls and no thermal bridging. This creates a more energy-efficient structure.

SIPs can be made in various sizes and thicknesses to fit building specifications. In most cases, the manufacturer sends the panels directly to the jobsite. Another benefit of using SIPs in new construction is the ease with which the panels fit together. Several DOE Solar Decathlon teams enjoyed this advantage during construction stages.

SIPs cost about 15% more than standard stick frames. However, the tighter insulation can result in a 40-50% decrease in energy bills. The initial investment usually makes the most sense for new construction efforts.

According to Stanford’s Best, the project manager, the home’s market appeal distinction came as a great validation of both the livability of this Bay Area home but also the marketability of the Stanford team’s core concept.

The judges commented: “The inside offered great open space and well-defined, functional floor plan. The high ceilings made the house seem more spacious. The integration of the indoor and outdoor spaces was exceptionally well done. The detail on user interface and fixtures of control system was notable.”

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