Retired architect William M. MacMullen fondly remembers the Ocean Colony Landing project he designed 12 years ago. Located in Marshfield, Mass., the 50 homes cost half the area average. Each unit had R-30 walls and heating bills of less than $500 each season. To top things off, the groundbreaking took place in May and the units were occupied by September of the same year.
How were these houses so energy efficient and so quick, and therefore cheaper, to build? The answer, according to MacMullen, is they were constructed with structural insulated panels (SIPs).
By now familiar to most builders, SIPs are made from expanded polystyrene (EPS) or polyisocyanurate rigid foam insulation sandwiched between two structural sheets of oriented strand board. About 12,000 homes were built with SIPs in 2002, according to the Gig Harbor, Wash.-based Structural Insulated Panel Association.
Considering how many houses are erected annually, this number is barely a blip on the national radar. The technology, however, is gaining acceptance. Even the nation's largest home builder, Pulte, is testing the viability of producing large quantities of SIPs houses.
“It would be huge if the No. 1 player in the home building industry adopted SIPs,” says Frank Baker, chief executive officer for Insulspan, a SIPs manufacturer. “It is a credibility thing for the industry.”
ENERGY SAVER One of the main advantages SIPs offer is energy efficiency. A 1999 Oak Ridge National Laboratory study found that the R-value of a wall with a 3½-inch EPS core is 14 compared with 9.8 for a 2x4, wood-framed wall insulated with R-11 fiberglass insulation. This kind of energy performance is one reason the Atlanta-based Community Housing Resource Center, which supports low-income housing, is investigating the technology.
According to M. Scott Ball, the center's co-executive director, the R-values of batt insulation are based on the assumption that a house will be built perfectly. “If the house is built poorly, then the R-values go down,” he says. “[But] SIPs have constant R-values.”
At last year's International Builders' Show in Las Vegas, famed architect Sarah Susanka and building science consultant Steve Easley teamed up on the Home by Design show house. Cosponsored by Nevada Power, the structure was built with SIPs from Insulspan. Baker says the house is 60 percent to 70 percent more efficient than a home that meets the model energy codes. A typical Energy Star-rated home has to perform 30 percent more efficiently than the model energy codes, he says.
SIPs also offer interesting design opportunities. Architect Michael McDonough used panels in his experimental e-House in New York's Hudson Valley. The house not only incorporates a laundry list of high-tech features and alternative building technologies, it features two cantilevered rooms that protrude from opposite ends of the building's stone-clad shell.
“We could not have done the two ‘view catchers' without SIPs,” the architect says. “It would have been enormously complicated to get the same R-values with traditional framing. It would have required much thicker walls, which would have been expensive.” Traditional framing also would have made the cantilevered areas heavy.