Traditionally, builders have used caulks and sealants to plug gaps in building envelopes. The exception is the shim spaces around windows and doors—the impracticality of sealing those spaces with caulk meant they were usually just stuffed with fiberglass insulation torn from a batt. But while the fiberglass offered some insulation value, it did next to nothing when it came to preventing airflow.
Caulks still have a place in air sealing, but fiberglass no longer cuts it for shim spaces. Adhesive spray foams have become almost mandatory. Tougher energy codes and more demanding customers have led manufacturers to improve their formulations, with the best products providing an air seal, flexibility, and water resistance—a combination not possible with early foams.
The International Energy Conservation Code now requires that new homes and additions be visually inspected and blower-door tested for airtightness. At the same time, customers are increasingly intolerant of drafts and discomfort, a trend that’s being confirmed by market research. “We have used Google Analytics and other research tools to try and understand what consumers are thinking about,” says Allison Fortune, North American retail manager for Dow Building Solutions. “We are seeing an increasing interest in air sealing.”
Properly sealed shim spaces make a home more comfortable and efficient. According to Dan Chiras, founder of the Evergreen Institute in Gerard, Mo., a 1/8-inch-tall, 6-foot-long crack next to a door jamb has the same amount of clear space as a 9-square-inch hole in the wall. Such gaps bring unconditioned air and moisture into the house, raising the load on the HVAC system and increasing the chance of mold and rot.
Adhesive spray foams offer better R-values than batt stuffing and make a tighter air seal. These products often are described as low-expansion, but the more accurate term is low-pressure. “Low-pressure foams don’t expand as rapidly or with as much force, so when they hit the window they don’t push on it very hard,” says Zachary Utz, product marketing manager with Fomo Products. In fact, the American Architectural Manufacturers Association’s (AAMA) standard 812 addresses pressure, not expansion: It requires that a foam not develop enough pressure to distort window or door frames. Any foam sold for this application obviously should conform to AAMA 812.
Open or Closed
Conforming products may be open or closed cell, depending on what blowing agent they use. The carbon dioxide used in open-cell foams off-gasses as the foam cures, while a closed-cell product’s insulating gas is permanently trapped in the foam.
Closed-cell foams offer higher R-values than open-cell products (an average of 5.5 per inch compared with 3.5), as well as 1/10 the moisture permeance. The only drawback with closed-cell products is that they tend to be inflexible. If the framing shrinks, it could pull away from the dried foam and open up gaps that air can flow through. Open-cell products offer more flexibility and thus are able to better accommodate frame movement.
Manufacturers have responded with hybrids that they say combine the advantages of both product types. “Our product is not 100% closed cell because you have to combine properties,” says Jim Katsaros, an R&D team leader at DuPont Building Innovations. “If it was completely closed cell, it would be too rigid. If it was fully open cell, it would be easier to work with but too permeable to air infiltration and water.”
At least one manufacturer is marketing its product specifically as a hybrid. Bill Longo, marketing manager at DAP, says his company’s closed-cell Draftstop 812 foam (named for its conformance to the AAMA 812 standard) has less than 0.1% water absorption yet stays flexible even when fully cured, with a 30% joint movement capability. “You can lay down a long, thin bead, let it cure, then tie it in a knot,” he claims.
Water resistance isn’t part of the AAMA standard, but if Longo has his way, it will be. He says that DAP and Tremco (its sister company in the commercial market) will introduce a proposal to include a water test, as defined by ASTM standard D2842, to the qualifying criteria for AAMA 812. This, of course, would give an advantage to closed-cell products. (As of early September, the AAMA said the proposal had not yet been submitted.)
That effort may be aided by a market that seems to be putting more value on closed-cell products—Fomo’s Utz says that these foams are gradually becoming the standard. “Our product has always been closed cell,” he says. “But now we’re seeing an overall shift in the industry, with other manufacturers moving to closed cell as well.”