Anything that can be called green is hot–and getting hotter–these days, but when the subject is residential building, all the talk about carbon footprints, sustainability, clean energy, and appliance efficiency is just that unless the building envelope is addressed. A really efficient HVAC system is just as efficient conditioning outside air as it is indoors, which is exactly what it will do if the building isn't properly designed.

STYROFOAM SIMPLICITY: Above, two subcontractors cut and install Styrofoam SIS® on a new home; the installation is completed in one pass around the home (bottom). Photo: Courtesy Dow Building Solutions A major breakthrough in building envelope integrity was achieved with the advent of house wrap and its ability to keep moisture and wind out. Heavier insulation on the inside, radiant barrier on the roof, and insulated concrete have helped as well.

Dow Building Solutions has come up with an even more efficient way to ensure the integrity of the building envelope: a new product called Styrofoam SIS® Structural Insulated Sheathing that goes further and provides a barrier to moisture and thermal intrusion. It thus can improve a home's HVAC efficiency by up to the 40 percent that the U.S. Department of Energy estimates is lost to the great outdoors by the average house.

It replaces OSB–or even plywood, for the few builders that still use the latter–which, it turns out, is a good idea from an energy efficient standpoint.

"When you use house wrap and OSB, you have zero insulation value," explains John Hammer, residential market manager, North America, for Dow Building Solutions. Still, he notes, "Some builders are very traditional. They have always used wood; it has an inherent structural feel to it.

"We have worked for years with builders to come up with a product that delivers multiple functions," says Hammer. That product is Styrofoam SIS® , comprised of a sandwich of structural shear bracing; a closed-cell, moisture-resistant rigid polyisocyanurate foam core with excellent compressive strength and long-term, stable R-value; and a durable, non-reflective, BLUE? water-resistant exterior.

William Gloede The product comes in the same standard-sized sheets as other materials and requires no additional house wrap. It can be nailed or stapled and cut with a standard circular saw. "You put this up just as you would OSB and plywood, tape the seams, and you're done," says Hammer.

Better yet, it weighs about two-thirds less than OSB, making it easier to schlep up ladders and scaffolds and move into place. Dow claims it's comparable in cost to the OSB/house wrap combination, particularly because its installation is accomplished in one pass around the house as opposed to two distinct operations with OSB and wrap.

Structurally, Styrofoam SIS® meets all codes for integrity. I ask Hammer if it could withstand a blow from an out-of-control riding mower. Dow has never tested such a thing, so he can't answer–I neglect to tell him that I have a Kubota front-loader with a 5-foot rear-deck finish mower on the back, and that I had unintentionally performed that very test on OSB clad with vinyl; the results were not pretty.

The Styrofoam SIS® should be available later this year through Dow's national distribution network in either half-inch or one-inch widths, the former with an R-value of 3 and the latter at 5.5. That's a selling point for the buyer, as is Dow's claim that the product is made from 80 percent recycled materials–the sustainability thing, once again.

That last claim leads to my next question, which, apparently, is something one should never ask of a Dow employee. It seems that Dow invented–and patented–Styrofoam, and, much like Band-Aids and Kleenex and Xerox, it has been co-opted by the public to describe everything that is made of a foam-like substance.

"Is Styrofoam SIS® made from recycled coffee cups?" I ask.

Without missing a beat, a stern Hammer replies, "There has never been a Styrofoam coffee cup. Ever."