Once upon a time, the average house was poorly insulated or it had no insulation at all. Today we know better. We’ve realized just how important insulation is for creating an energy-efficient house.

“With energy costs rising and energy sources diminishing, conservation is critical for our earth’s future,” says Scott Miller, director of public affairs and sustainability at Shelbyville, Ind.–based Knauf Insulation. “Insulating buildings is the single most important factor in ensuring a sustainable future.”

The question, however, is whether or not today’s builders are insulating their houses with the newest technology or doing what they’ve always done.

When it comes to insulation, builders and architects have their favorites. Most stick to fiberglass batt, the dominant product in the category; but in recent years, other options have emerged such as cellulose, foam, natural fiber, wool, and most recently blow-in fiberglass.

Manufacturers say there is a reason that builders choose fiberglass: “It offers the most features and the most benefits,” says Miller. “It’s made from an inert material, doesn’t burn, and is available in a wide variety of R-values, from R-13 to R-22.”

Architect Ken Wilson in Washington, D.C., is a fan of fiberglass’ cost and performance, especially the formaldehyde-free version from Denver-based Johns Manville. But for others, fiberglass no longer supplies the kind of energy performance they desire. Architect John Dennis Murphey, for example, used to spec his homes with 2x4 studs and fiberglass insulation. He no longer does so. The problem, Murphey says, is that fiberglass batts do not completely fill wall cavities and leave too many spaces where air infiltration can occur.

“We’re in an area [of the country] where you don’t know what it’s going to be outside,” says Murphey, principal of Chevy Chase, Md.–based Meditch Murphey Architects. “We’re in the middle, so it could be cold, rainy, or hot and humid.” For this reason, Murphey switched to 2x6 studs in the 1980s, and he started using closed-cell foam insulation about a year ago. Murphey favors foam because it offers high-insulation value, tightly seals wall cavities, and prevents air leaks. “Leaks bring in humidity, and humidity brings in lawyers,” he says.

Foam creates a superior air seal, which minimizes air leakage to deliver advanced moisture control, healthy air, and energy savings of up to 50 percent, says Ontario, Canada–based foam manufacturer Icynene. Valley Forge, Pa.–based CertainTeed, which recently added a foam product to its lineup of insulation offerings, says foam minimizes hot and cold spots and provides outstanding comfort.

But foam is an expensive option, though architects who use the product say the energy savings pay for the extra cost. It’s also a petroleum-based product, the manufacture of which contributes to greenhouse gases, says Miller. ­“Petroleum-based [insulation] products have no future.”

In recent years, blow-in cellulose has become popular, and many architects believe it’s a good alternative to fiberglass and foam. Architect Angela Dean, principal of AMD Architecture in Salt Lake City, is a fan. Dean specifies her walls with 2x6 framing and blown-in cellulose (she uses foam if the budget permits). “By code, you can still get away with 2x4 framing [and fiberglass], but it’s not a good idea,” the architect says.

Jenison, Mich.–based Nu-Wool says its environmentally friendly cellulose insulation is made from recycled newsprint and offers a 40 percent savings on energy bills.

Johns Manville says it has developed the ultimate insulation product, Spider. Offering the performance of a blow-in product and the value of fiberglass, Spider increases R-values and completely seals the nooks and crannies where air leakage and infiltration may occur. The company says Spider is the product the industry has been waiting for.

“Builders are increasingly seeking insulation products that provide minimal insulation gaps and voids to help them build more energy-efficient homes,” says Tony Fonk, residential channel leader for Johns Manville. “In addition, they are demanding systems that allow quicker and easier installation, fewer callbacks, and reduced risk of mold and mildew.”

No matter what insulation you choose, there are a few things to remember. Installation is key. The product must completely fill the wall cavities, architect and building scientist Peter L. Pfeiffer explains. Pfeiffer, principal of Barley & Pfeiffer Architects in Austin, Texas, says the home building industry must not think simply about insulation but should instead think in terms of “total wall efficiency” based on regional climate. Because almost all homeowners in every region of the country use air conditioning in the summer, the house has to be tight and efficient to contain the cooling, he notes.

Lastly, Miller says, ignore the building codes. “We’re not a proponent of insulating to code,” he says. “You should do as much as possible during new construction. Doing it later will only cost more.”

Learn more about markets featured in this article: Salt Lake City, UT.