With a complex roof that has many intersections and valleys, as at Carlisle, Tom will roof right over the SIPs, but first the installers, in addition to joining the panels with flexible caulk, inject a foam sealant into the joints and tape the underside of the panels. They also tar the seams as a temporary measure before the roofing goes on. Tom takes an extra precaution by covering the whole roof with a layer of waterproof membrane before he lays the shingles.

Still another advantage of SIPS is that they're environmentally friendly. First, they help conserve old-growth trees, since the OSB panels are made of fast-growing sustainable wood. And the controlled factory environment means less job-site waste and more recycling. Also, the foam itself is inert, and its manufacture does not use ozone-depleting chemicals. Making the foam, on the other hand, does require toxic substances, like benzene, a known carcinogen. Environmentalists are also concerned about the addition of widely used brominated flame retardants, which may be toxic and are probably "bioaccumulative," meaning they hang around the environment forever. But Alex Wilson, editor of Environmental Building News, still gives SIPs high marks. "There are some issues related to materials used in SIPs, but because they allow us to build energy-efficient homes, they are considered green," he says.

Two downsides of SIPs: They can be a draw to insects (unless treated with boric acid), and rodents can be attracted to the warmth of their insulated wall cavities. Another complication associated with SIPs is running wiring in the walls. SIP panels can be ordered with predrilled channels through the foam, designed to accommodate wires at standard heights for outlets and switches. (Plumbing chases can also be predrilled, although in cold climates you shouldn't run anything but a vent pipe in an outside wall.) Another wiring solution is to use baseboard outlets, available in a range of styles. The most versatile method is to cut vertical slots into the SIP panel (through the wood and about half an inch into the foam) using a plunge router. "That gives you the flexibility to run wires wherever you want," says LeRoy. Drywall covers the slots, and because the walls are so straight and completely sheathed in wood, even that goes up more quickly and with less waste.

Running the Numbers

Though it would seem that the speed of SIP construction would automatically lower costs with savings on labor, that isn't always the case. The actual cost relative to conventional stick-frame houses depends on where you live. In southern climates, where job-site labor is fairly cheap and energy standards more relaxed, SIPs are generally more expensive than conventional framing. But in the North, SIPs can be competitive with 2-by-6 walls and spray foam. (Six-inch-thick custom-cut SIPs, like the ones at Carlisle, run $4.50 to $5.50 per square foot delivered.) To find out whether there's a cost benefit to SIPs in your area, contact a manufacturer (www.sips.org has listings), who will run your house plans through their computer and give you a precise estimate at no charge. Then you can take that figure to your builder and stack it up against other options.

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