Launching a new production-level homebuilding company at perhaps the lowest point of the housing recession, and in one of its poster cities, might seem daunting. But Joseph Carl Homes in Phoenix had a hook: an integrated approach to thermal performance and energy efficiency that pushed its HERS (home energy rating scores) count far beyond those of its large rivals while maintaining a competitive price.
To achieve that, Joseph Carl Homes employs a variety of insulation products to optimize their effectiveness. It's a "the sum is greater than its parts" method that also helps keep the cost of any one insulation component in check. "There's a slight cost premium [to this approach], but it helps us sell more homes faster [than the competition]," says Ken Kulinowski, the builder's vice president of purchasing.
Combining multiple insulation products to achieve greater thermal performance has been the battle cry of building scientists for decades. Only now–thanks to consumer demand, public sector support, tighter regulatory standards for home energy efficiency, a proliferation of insulation options, and a critical mass of builders searching for any sort of sales edge–is that message getting through.
"Builders now have insulation products at their disposal that allow them to determine where and how they best apply," says Mark LaLiberte, a Denver-based building science consultant and educator. "If you mix and match these products, you can significantly improve thermal values."
The Hybrid Solution The approach gaining the most popularity, for both walls and roofs, is called "flash and batt." Once the exterior sheathing is applied to the building's frame, a 1-inch layer of high-density (aka closed-cell) polyurethane foam is sprayed into each framing cavity. The cavity is then filled with either rolled fiberglass batt, blown-in-blanket (BIB), or sprayed cellulose insulation.
The "flash" of foam serves two purposes. At around R-6 per inch of thermal resistance, the dense foam layer is an effective insulator, especially in heating climates where cold outside air wants to gravitate to the warmer indoor environment. More important, however, the flash layer completely seals the cavity from air infiltration through the exterior sheathing and any service penetrations through the perimeter shell.
"One of the most effective things to improve energy efficiency is air sealing," says Dave Wolf, the technical leader for EnergyComplete, a new hybrid insulating solution from Owens Corning. Block air infiltration, he says, and you stop not only thermal transfer but also the moisture vapor carried by that air that can lead to mold and structural degradation.
Batts or BIBs? Suppliers and building scientists debate the merits of using traditional rolled batts to supplement the foam and fill out the cavity. While certainly less expensive and easier to install than a BIB or cellulose system, "batts are nearly impossible to install correctly," says LaLiberte.
Batts quickly lose their ability to resist thermal transfer if they are compressed into the cavity and cut or worked around mechanical runs; spending the time to carefully and properly install them and accommodate those runs without degrading R-value, says LaLiberte, can cost as much in extra labor as a blown-in fiberglass product, which more easily and completely fills the framing cavity.
Advocates of the flash-and-batt solution, including Wolf and the "critical seal" approach of the EnergyComplete system (in which a latex-based foam sealant is applied only to gaps and penetrations before fiberglass fills the rest of each cavity), warn against using lower-density, open-cell (e.g., Icynene) foam for the flash component.
While less expensive than closed-cell, an open-cell spray is far more difficult to control to get a 1-inch layer and is about half the R-value per inch, says Wolf. Better, say experts, to apply that product to the entire cavity in non-living areas such as an unfinished, unvented attic.
–Rich Binsacca is a contributing editor to ProSales.