As the cost of heating and cooling homes has escalated—along with codes and regulations requiring greater energy conservation measures in residential construction—builders have had to become increasingly innovative in making their structures more energy efficient.
One of the best ways to improve insulation values in the field is to seal any and all gaps, joints, and intersections between construction materials in a building’s exterior shell before installing insulation. Preventing air infiltration has a threefold benefit: It keeps outside heat or cold from entering, stops interior conditioned air from escaping, and allows the insulation to function at its rated R-value.
Early adopters of this strategy used off-the-shelf products, such as caulking and expanding foam insulation, as draft-stopping materials. In some cases, this approach adds little or no insulating value and is used mainly to restrict the passage of air. Expanding foam is especially handy for this task—available in disposable single-use cans, it not only ensures better draft-sealing, it also fills joints and crevices of almost any size or shape. Builders in colder climate zones “double down” on this technique by completely coating framing cavities, including the backside of exterior sheathing, with a 1- to 2-inch layer of insulating foam. This practice, generally referred to as “flash and batt,” adds cost but increases the performance of the building section and adds to the R-value of the batt or blown-in insulation applied afterward through reduced air leakage.
As these techniques developed, energy performance recommendations and requirements for reducing air infiltration were increasing on a parallel track.
Energy Star v3.0 requires that virtually all penetrations or gaps in the building envelope—at exterior sheathing joints, sheathing-to-framing joints, wall-to-roof joints, and other contact points where exterior air can enter or conditioned air can escape, including between drywall and the wall framing’s top plate below an unconditioned attic space—be “fully sealed” with caulk, foam, or an equivalent gasket material. Revisions to the International Energy Conservation Code for 2012 limit whole-house interior/exterior air exchanges to just three per hour, reduced by more than half the previous code cycle’s maximum of seven per hour. The DOE’s Builders Challenge program goes even further, calling for increasingly stringent air-sealing thresholds based on climate zones and advocating just 1.5 air changes per hour in homes built in specific northern locales. The next versions of the LEED for Homes rating system and the ANSI National Green Building Standard, both in review, are also expected to increase air-sealing requirements.
Today, a number of manufacturers sell complete “hybrid” air-sealing and insulation systems that combine proprietary gap-sealing, vapor barrier, and insulation products. Most of these systems require specialized application equipment and installer training and certification, but they provide a single-subcontractor, air-sealing, and insulating solution to help builders meet the new code requirements.
“We’ve done testing on several of these systems,” says Amber Wood, an energy program manager at the NAHB Research Center. “Decreasing your air infiltration has a huge impact on energy efficiency. It’s more costly, but you end up with better insulation.”
Wood acknowledges that tighter structures typically require some kind of positive ventilation device, such as a mechanical heat- or energy-recovery ventilator, but she says the energy savings over time offset the additional cost. She adds that air sealing also results in homes that are less drafty and less prone to water intrusion, and it helps to keep out pests, such as insects and vermin.
Matt Girand, a product and program director for residential insulation with Owens Corning, which offers a hybrid air-sealing and insulation system, says the adoption of air-sealing and flash-and-batt techniques gained momentum slowly but has become widely accepted. “We launched our system three years ago, and there wasn’t much conversation about air sealing then,” he says, “but now builders are asking for it. Energy Star has certainly pushed it forward.”