Two years ago, when a small lot next to my property became available, I bought it with the idea of building a small, inexpensive, energy-efficient and affordable rental house on the site. After researching the possibilities of building a conventional stick-frame structure as well as using alternative construction methods, I finally settled on the design of the house next door, and I'm ready to build it using structural insulated panels, or SIPs. SIP is a buzzword increasingly heard in home construction these days. Each SIP is a sandwich, typically two pieces of 7/16-inch oriented strand board (OSB) on either side of a rigid insulating foam core. Butt these panels together with simple fasteners and they take the place of conventional 2x6 or 2x4 framing, fiberglass insulation and plywood sheathing. Various types of splines - narrow strips of wood or OSB - hold the panels together edge to edge and seal the joints against air infiltration. I was introduced to SIPs when I helped two friends, Ron and Kate, erect their SIP home. I was impressed during construction by the fact that just a few of us, with relatively little construction experience, were able to erect the house ourselves and, after construction, by just how comfortable and energy efficient the house was.

Benefits of Using SIPs

Although an increasingly popular method of construction only in the last decade or so, the roots of SIPs go back many decades. Frank Lloyd Wright toyed around with SIP-like panels in the 1930s, and Alden B. Dow, son of the founder of Dow Chemical Co., designed the first SIP homes in the early 1950s. Interest in SIPs got a jump start in the 1980s as manufacturers started developing new products and streamlining SIP production, and in the last few years that interest has soared. Among other organizations, Habitat for Humanity now uses SIPs for some of the homes it builds. Why all the buzz about SIPs? Simply put, SIP construction results in homes that are: Strong SIP homes proved their durability in the 1993 earthquake in Kobe, Japan, and during recent hurricanes in the southeastern United States. Energy efficient The energy efficiency of SIP homes results from the high insulating value of the panels and their resistance to air infiltration. (A SIP home should have an air-to-air heat exchanger to exhaust stale air and bring in fresh air.) Without the cold spots and extensive substitution of framing material for insulating material of conventional stick framing, stated R-values for SIP homes come close to matching actual R-values. No vapor barriers are necessary because the closed-cell foam insulation has a low permeability rating. Quick to install Typically, it takes just a few days to erect the shell of an average-sized SIP home. Environmentally friendly The wood used in SIPs is low-quality hardwood and plantation thinnings or wood waste that could not be used for framing lumber. There also is less waste in the construction process when SIPs are used. Other benefits of SIP construction become obvious once you're living in the house. For instance, when Ron and Kate decided they wanted to add a window in their home's upper floor, they did not first have to open the wall to hunt for studs and then build headers. After checking for electrical wiring, they just cut an opening, imbedded 2x6 nailers (or 2x4 nailers, depending on wall thickness) and popped in the window. When it came to hanging kitchen cabinets, again, there was no need to find studs. Kate just screwed the cabinets right into the OSB. Drywall was easy to apply, too, since there was no need to hunt or plan for nailers. And because of the dimensional stability of SIPs, the finished drywall in their home has not developed cracks. We've also noticed how quiet the house is; the SIP panels excel at blocking outside noise. Perhaps most important is how little energy is required to heat and cool the house. When compared with conventionally framed homes, typical energy savings range from 12 to 17 percent for SIP homes, though savings as high as 50 percent have been reported.

Types of SIPs

SIPs are available in various dimensions and made of various materials. The facing material is usually OSB, but you can purchase panels with a finished tongue-and-groove wood facing that is ideal for decreasing the time and expense needed to complete construction of a cathedral ceiling. Two types of rigid foam are used in SIPs: expanded polystyrene (EPS) and polyurethane (polyisocyanurate). EPS is 10 to 15 percent cheaper than urethane but has only about 60 percent the R-value (R-23 versus R-38 for a 6.5-inch wall). Ron and Kate used EPS panels, but I've decided to use urethane panels. Although the panels themselves cost more, the same insulating value can be achieved with thinner panels, so shipping costs are lower. In addition, I can use narrower, and therefore cheaper, lumber to trim window and door openings. Both types of insulating materials have Class I fire ratings, which means that although they will burn, they cannot maintain fire by themselves. Urethane maintains its structural integrity right up to the point of melting. Stock panels range from 4 feet to 9 feet wide and up to 28 feet long. Foam thicknesses range from 4.5 to 12.5 inches. Most panels come with chases for electrical wiring. You can cut openings for windows and doors on-site, or you can order the panels precut from manufacturers. To determine which will work better for you, balance the increased cost of precut panels against the savings in time, labor and cleanup. Weighing in at about four pounds per square foot, a relatively large SIP is easy to maneuver. Ron and Kate primarily used 14-by-4-foot panels, 6 inches thick, which four of us were able to put in place with ease. We used a circular saw to cut the panels, cutting from both sides, but specialized deep-cut saws can speed up this job and are a must for thicker panels. The other specialized tool for working with SIPs is a hot knife or router for scooping out pockets in the foam to accept standard building materials if window and door openings are not ordered precut by the manufacturer.

Building With SIPs

Good construction begins at ground level, and with SIP construction, accuracy at ground level is all-important. The panels are attached to 2x dimensional lumber shoeplates that are the same width as the space between the OSB boards and are bolted to the deck, slab or foundation. Foam at the base of the SIPs is scooped out 1.5 inches deep so the standing panel can fit right over the shoeplate and is secured to it with screws or nails through the OSB into the plate. Once we had two corner panels secured in place, we progressed along the shoeplate panel by panel. Adjacent panels are secured according to manufacturer recommendations, usually with some sort of spline between panels that is screwed or nailed in place. As each panel of Ron and Kate's home went into place and was secured - a matter of only half an hour or so for each one - another 56 square feet of wall had been erected, the equivalent of framing, sheathing, wrapping and insulating in conventional construction! There are several options for constructing a second-floor platform without compromising the insulating properties of the SIPs or their resistance to air leakage. For instance, you can cap first-floor panels with a deck, upon which the second-floor panels are raised on a shoeplate, in the same way the first-floor panels were raised from the first-floor deck, slab or foundation. Alternatively, if the first course of panels is long enough to span both floor heights, ledgers for the second-floor deck can be embedded into the panels. This is the option Ron and Kate chose, and the one I'll use for my new house.

Up on the Roof

Much of a home's heat is lost through the roof, and the roof is where SIPs really shine. Panels are self-supporting to spans of about 15 feet in normal snow-load areas, so the only support the panels on my new house need is a ridge beam supported at the two gable ends. Panels for larger roofs can be supported with the help of purlins (horizontal rafters) or trusses, either of which can enhance the beauty of a structure. Lifting a large panel to a roof is difficult if not downright dangerous, especially if it's windy, so it is necessary to hire a crane for this phase of construction. With various temporary attachments, each panel can be hoisted into place in a matter of minutes. Splines join roof panels together just as they do wall panels; joints for longer spans get structural splines. When all panels have been secured in place and after windows, doors and wiring have been installed, remaining pockets are insulated and sealed with spray foam. We foamed all joints through holes drilled every 8 inches to foam channels in the panels. Although construction went fairly smoothly on Ron and Kate's house, I'm planning on hiring an experienced crew to erect the SIP shell of my home. I hope to avoid some alignment problems (cured with spray foam) and some harrowing moments that occurred when installing the roof panels on Ron and Kate's house, which resulted from our inexperience. In addition, a professional crew should be able to close in my house in a couple days. Should you decide to go this route, many manufacturers of SIPs can recommend builders in your area who have experience working with their panels.

Finishing Touches

Finishes for a SIP home are the same as for a conventionally built home. The goal, in either case, is for the finish to look attractive and keep out moisture. The OSB on the outside of the roof panels can be treated just like the OSB or plywood that sheaths conventional roofs. The only wrinkles when applying siding on a SIPs home are to use extra nails and to use nails that are no longer than necessary to penetrate the OSB. Inside, the usual wall treatment will be half-inch drywall. Although we didn't have to locate studs to attach drywall or cabinetry in Ron and Kate's house, we did use the recommended fasteners to attach cabinetry, because OSB has less holding power than studs. In the end, SIP homes generally end up costing about the same as stick-built homes. A higher cost of materials and a slightly increased cost for installing wiring and plumbing are offset by a savings in waste and in construction labor. Much depends on a design that capitalizes on the spanning capabilities of SIPs. Of course, Ron and Kate saved a lot of money by putting up their home themselves. Once any SIP house is occupied, however, the real savings kick in because of the great energy savings SIPs provide, month after month and year after year.

Lee Reich has worked in agricultural research for the U.S. Department of Agriculture and for Cornell University. He lives in New Platz, N.Y.