All About Structural Insulated Panels and House Framing

Paul and Peggy Dunckers' residence in Wilson, Wyo., is the kind of house you might expect a pair of architects to design for themselves: hip, budget-minded, energy efficient. The 1,900-square-foot farmhouse has exposed, split-faced concrete blocks, radiant heated concrete floors, geothermal heat, and a metal roof. It also has another, hidden, feature: The roof and walls are constructed entirely of structural insulated panels (SIPs). [CAPTION: The Insulspan SIP walls and roof of this Michigan home handle the complex roofline and the 25-foot great room ceiling. Photo courtesy Insulspan]

By now familiar to builders, SIPs are energy-efficient building panels made from expanded polystyrene (EPS) or polyisocyanurate rigid foam insulation sandwiched between sheets of oriented strand board (OSB). About 12,000 homes were built with this technology in 2002, says the Gig Harbor, Wash.-based Structural Insulated Panel Association (SIPA).

Considering how many houses are built in the United States, this number is barely a blip on the national radar. The technology, however, has come in from the fringe and is steadily gaining acceptance as an alternative to stick framing. Architects and manufacturers say the technology is a viable design alternative, too, and believe that it is only a matter of time until it will be the dominant method used to build homes.

Lofty ambitions

One of the main advantages that a SIP house has over stick framing is energy efficiency. A 1999 Oak Ridge National Laboratory study found that the R-value of a wall with a 3 1/2-inch EPS core is 14 compared to 9.8 for a 2x4, wood-framed wall insulated with R-11 fiberglass insulation, SIPA says. This kind of energy performance is one reason the Atlanta-based Community Housing Resource Center has been investigating the technology.

"Our primary interest is that we are in the South, and the temperature is hot and humid," says M. Scott Ball, co-executive director. "We need to stabilize the temperature of affordable housing, and we think that hollow cavity walls are a petri dish for mold and mildew." According to Ball, the R-values of batt insulation are based on the assumption that a house will be built perfectly. "If the house is built poorly, the R-values go down. SIPs have constant R-values."Because construction techniques have changed, Ball says, stick framing is no longer the best method. Houses are tighter because of housewrap and the improved performance of windows and doors, Ball explains, so when a leak occurs, batt insulation sucks up water like a sponge. This encourages mold and mildew growth.

To prove that SIPs can build better walls, as well as look aesthetically pleasing, the group built a demonstration home to research building methods and products and to question some of the long-held assumptions about stick framing. Located in Atlanta, 943 Bruce Circle, is a 2,000-square-foot, industrial-style house built with concrete floors, recycled building products, exposed joists, and 6-inch-thick SIP walls with an R-value of 25. Because the house has only two load-bearing walls, it features a loft-like interior that can be reconfigured if the homeowner's needs change. [CAPTION: Despite the large window openings, the natural gas cost per year is about $500 for heating, hot water, and appliances. Photo Courtesy Insulspan]

Weight watcher

Architect Michael McDonough is also impressed by the design potential of SIPs, which is why he is using the panels in his experimental e-House under construction in New York's Hudson Valley. McDonough developed the e-House with a team of engineers, scientists, and environmentalists to see how the house will perform over time. As a technological exploration, the e-House incorporates a laundry list of high-tech features and alternative building technologies; as a design exploration, 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.

The Dunckers, too, realized a similar opportunity while they were designing their Wyoming residence. "We designed the house to be stick built but decided to use SIPs for the roof, after we found out that we could have exposed rafter tails," says Peggy Duncker, a principal at Tobler Duncker Architects in Jackson, Wyo. "Meanwhile, [the panel company] wanted to see how much it would cost to do the walls with panels." After its calculations, the panel company found that the Dunckers could get SIP walls for the same price as stick-framed walls.

At the January 2004 International Builders' Show in Las Vegas, SIPs had an opportunity to show off their design potential. Famed architect Sarah Susanka and building science consultant Steve Easley teamed up for "Home By Design," a show home that was a multi-media design and technology tutorial for builders. Co-sponsored by Nevada Power, the house was built with SIPs from Blissfield, Mich.-based Insulspan. Company CEO Frank Baker says the house was 60 percent to 70 percent more efficient than the model energy codes. A typical Energy Star-rated home needs to perform 30 percent more efficiently than the model energy codes, he says.

Point, counterpoint

Of course, a technology such as SIPs is not without its questions, and even pros who are fans say there are kinks to work out. For one thing, building a house with SIPs can be comparable to stick framing, but it is generally not cheaper.

"There are engineering solutions that make sense for SIPs," says Mike Bryan, division manager for panels at SIPs manufacturer Premiere Industries in Fife, Wash. "Some areas have high [stick-framing] labor rates, and it makes sense to use SIPs to reduce the cost." Still, stick framing is cheaper because the lumber infrastructure is there and has been for a long time, he says. "In the panel industry, the infrastructure is not totally in place. Once it is, the price will come down and will be less than stick framing."

But other issues exist. "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 life-span 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 life-span of the bond between the OSB and the foam? Based on his experience, Ball says SIPs take some time getting used to, they are heavy, do not do complex roofs well, and are difficult to wire. "Despite what manufacturers say, electricians hate fishing wire through the foam." Ball still believes, though, "that in the next few years, SIPs will be the biggest thing going."

"For me, as an architect, it is still a bit new," says Duncker. "It is not a tried and true product like stick framing, so people are reluctant to use it." 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 SIPA, says most of the apprehensions people have about SIPs disappear once they use the product. On the wiring issue, he says most people use a built-up baseboard and run the wiring behind it. What about roofs? "For the most part, you can put up a more complex roof 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." Wachtler says that exposure to rain will not reduce the structural capacity of panels made with OSB and adds that it would be highly unlikely that an OSB skin would come apart from the foam core. If any delamination occurs, there are repairs that can be made, he adds.McDonough says most of the issues associated with panels are minor ones. "Like any material, there are negatives," he says. "But all of the things I ran into are manageable." For instance, he says, measurement tolerances can be a problem, so to combat this the architect allowed for an 1/8-inch expansion gap. "There is a lot of unexplored design potential for SIPs so I like experimenting with it."

Futures trading

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 Corp. in Brattleboro, Vt. "They look at panels as a wild and futuristic technology."[CAPTION: Panels such as these from Premiere Building Systems, come in different thicknesses for different applications. They range from 4 to 12 inches. Photo: Courtesy Premiere Building Systems]

Besides, demand in the production home market is bigger than the SIPs industry can supply right now. So, the question is, when will the panel industry come to the forefront? Recent moves by one of the nation's largest home builders, Pulte, suggest that it could be soon.

Three years ago, the Bloomfield Hills, Mich.-based builder built its own pilot plant in the Detroit area to investigate the viability of building large numbers of its 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." (Pulte did not return calls for comment.)

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. "It would be huge if the No. 1 player in the home building industry adopted SIPs," Baker says. "It is a credibility thing for the industry." If Pulte uses it, he says, others will follow.

Sidebar: 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 in Holland, Mich., make panels to specs. The panels work in conjunction with roof trusses, floor systems, and any other building product it takes to build your 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 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, 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, SIPA's Bill Wachtler 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. A helpful resource to reference during your roof selection is The Essential Guide to Roofing, which identifies everything from the basics to the most advanced techniques in roofing..

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 featured different window head heights. Her advice: Check shop drawings with a fine-tooth comb 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," he says and more stable. Another way to counter this is to add 1/8 of an inch allowance in your measurements, says architect Michael McDonough. "It's a good trick for when you are putting them in," he says. "They will fit much better."

Originally Published in BUILDER magazine