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.

Tobler Duncker Architects. Architect Peggy Duncker's house in Jackson, Wyo., is made of structural insulated panels (SIPs). The architect says despite their benefits, SIPs aren't a "tried-and-true product" so pros are relucant to try them. 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.”

Tobler Duncker Architects. Architect Peggy Duncker designed this home for her family in Jackson, Wyo., with structural insulated panels. The architect says construction of her SIPs house cost the same as if it were stick built, and that using SIPs didn't compromise the design. 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.

Furthermore, SIPs construction can be cost neutral when compared with stick framing. Peggy Duncker, a principal at Tobler Duncker Architects in Jackson, Wyo., designed her own home with SIPs. “The company wanted to see how much it would cost to do the walls with panels,” she says. “They came up with the identical price.”

LINGERING CONCERNS Of course SIPs are not without issues and questions, and even fans say there are kinks to work out.

“There are engineering solutions that make sense for SIPs,” says Mike Bryan, division manager for panels at SIPs manufacturer Premier Building Systems. “Some areas have high labor rates and it makes sense to use SIPs to reduce the cost.”

But Bryan says stick framing typically is cheaper. “In the panel industry, the infrastructure is not totally in place. Once it is, the price will come down and will be even less than stick framing.”

Other issues exist too. “There is still some concern about the long-term durability of the panels,” Ball says. And he has more questions: Is there any information on the lifespan of the binders that glue the OSB together? If the OSB delaminates to any degree, is there any remedy? Is there any information on the lifespan of the bond between the OSB and the foam?

In addition, Ball says, based on his experience, SIPs take some time getting used to; they are heavy, do not accommodate complex roof designs, and are difficult to wire. “Despite what manufacturers say, electricians hate fishing wire through the foam,” he contends.

“It is not a tried-and-true product like stick framing, so people are reluctant to use it,” adds Duncker. In addition, she asks, “What happens when the OSB gets wet and starts to rot? You just can't remove the siding and replace the OSB.”

Bill Wachtler, executive director of the Structural Panel Association, says most questions and apprehensions people have about SIPs disappear once they become familiar with the product. As for the wiring issue, builders can build up baseboard and run the wiring behind it. And Wachtler says complex roofs can go up a little faster with SIPs than with dimensional lumber. “You definitely have to plan ahead, but after you do it a couple of times, it becomes easier,” he says.

Exposure to rain will not reduce the panel's structural integrity, and it would be highly unlikely for an OSB skin to come apart from the foam core, Wachtler claims. If any delamination occurs, repairs can be made, he adds.

McDonough says most of the issues associated with panels are minor ones. “Like any material, there are negatives,” the architect says. “But all of the things I ran into are manageable.”

For instance, measurement tolerances can be a problem so McDonough allows for a 1/8-inch expansion gap. “There is a lot of unexplored design potential for SIPs, so I like experimenting with it.”

ON THE HORIZON At the moment, production home builders are not convinced that SIPs offer design potential and cost savings. This isn't surprising, most manufacturers and architects say. “Builders do not like to change the way they do things,” says Doug Anderson, sales manager for Winter Panel. “They look at panels as a wild and futuristic technology.”

But SIPs have piqued Pulte's curiosity. Three years ago, the Bloomfield Hills, Mich.-based builder constructed a pilot plant in the Detroit area to investigate the viability of building large numbers of homes with SIPs. “They found that if they made some changes, SIPs could work,” Bryan says. “They decided to build another plant in Virginia and they expect to churn out about eight houses a day.”

The importance of Pulte's presence cannot be overstated, says Insulspan's Baker. The builder's success is seen as a vitally important step in the widespread adoption of the technology.

This story first appeared in RESIDENTIAL ARCHITECT magazine.

Keep in Mind Structural insulated panels (SIPs) offer some benefits over stick framing, but architects and builders familiar with the technology say there are some things you need to watch.

  • DESIGN LIMITATIONS: The belief that panels limit design options is not true, manufacturers say. Companies such as W.H. Porter make panels to specs. The panels work in conjunction with roof trusses, floor systems, and any other building product it takes to build a home, so anything is possible. One caveat: When ordering windows and exterior doors, a finished window jamb of 5 1/16 inches after drywall is installed will be needed. Check with your supplier to see if there is any additional cost.
  • WIRING DIFFICULTIES: Wiring is typically done through chases in the wall that are 16 and 45 inches off the floor. M. Scott Ball, co-executive director of the Community Housing Resource Center that built a SIPs home, says, however, that electricians often encounter difficulties when pushing wire through the spaces. One solution is to use a heavier baseboard and run wires behind that. In addition, manufacturers recommend using vertical chases spaced every 4 feet. The electrician then simply drills access holes through the floor behind the walls.
  • LIMITED ROOFLINES: Some builders say complex roofs are hard to do with SIPs, but the industry says this is a myth. Dormers are actually easier to build with panels, Bill Wachtler of the panel association says. Complex roofs may take more planning because it is a different process, but they go up a little faster with panels than with dimensional lumber, he contends.
  • CAD DRAWING: Architect Peggy Duncker says that the construction of her house was great once the panels arrived on the site. The shop drawing process, however, was tedious. Any unusual designs can cause problems if they are not checked. The Dunckers' house features different window head heights. Her advice: Check shop drawings carefully before the panels are manufactured.
  • SPLINES: Panels are manufactured with strict tolerances of 4-foot widths and are connected with wood splines. Ball says dimensional lumber splines invariably warp, which makes it hard to notch the connections. That's why he prefers laminated veneer lumber splines. “They are perfectly straight,” and more stable, he says. Another way to counter this is to add 1/8 inch allowance in measurements, says architect Michael McDonough. “It's a good trick for when you are putting them in,” he says. “They will fit much better.”—N.F.M.
  • Resources

Architect Michael McDonough

Community Housing Resource Center

Structural Insulated Panel Association

AFM. R-Control structural insulated panels form a strong structural system consisting of Perform Guard expanded polystyrene (EPS) insulation laminated to OSB. They can be used for walls, roofs, and floors. Labor time savings range from 30 percent to 40 percent compared with stick building, the firm says. Panels are available in sizes from 4 feet by 8 feet to 8 feet by 24 feet. 800-255-0176.

Community Housing Resource Center. This organization that supports construction of affordable housing used structural insulated panels to build this dwelling in Atlanta. The center was drawn to SIPs because they offer lower, consistent energy bills for homeowners. 404-624-1111.

Tobler Duncker Architects. Architect Peggy Duncker designed this home for her family in Jackson, Wyo., with structural insulated panels. The architect says construction of her SIPs house cost the same as if it were stick built, and that using SIPs didn't compromise the design.

Premier Building Systems. Premier Panels are composed of two sheets of oriented strand board structurally laminated and pressure-cured to a rigid core of foam insulation. They come standard in many sizes and thicknesses. The company also offers accessories such as screws, ridge caps, and mastic. 800-275-7086.

Insulspan. The company's structural insulated panels (right and below photos) are solid, one-piece structural components that can be used in walls, floors, and roofs. Each panel consists of a expanded polystyrene (EPS) core bonded between two outer layers of rugged OSB. They form a strong, versatile building shell that can significantly shorten construction times, according to the manufacturer. Their energy efficiency generally allows heating and cooling equipment to be downsized, reducing initial capital costs and operating costs, the firm says. 517-486-4844.