Manufactured hybrid air-sealing and insulation systems vary widely in cost, application steps, and the way they approach air sealing and insulating.
Knauf Insulation offers EcoSeal, a liquid gap sealant that dries to a thin, elastic membrane. It is non-insulating and intended only to bridge and seal narrow gaps and cracks where building materials intersect. This water-based, solvent-free sealant is applied with a commercial-grade airless paint sprayer; installers require no protective clothing, and the structure does not have to be isolated during application or curing. Batt or blown-in insulation is recommended following application.
According to Patrick Hearne, a Knauf installer-certification instructor, EcoSeal is the easiest to apply and least costly air-sealing system available. A 2,000-square-foot home typically requires just two buckets of spray-on sealant costing less than $230 per bucket. Although Knauf recommends using approved installers, Hearne says, “the average builder can apply this if they go through the training and certification,” which Knauf provides at no cost.
A somewhat different gap-sealing approach, from Owens Corning, uses an expanding foam sealant with low insulating value. The EnergyComplete system improves on improvised flash-and-batt methods at “a comparable cost,” according to the company. The open-cell polyurethane foam used with this system also has a much higher density and greater flexibility than can-based expanding foams, allowing it to compress and recover to provide a better air seal. This is especially important for difficult-to-seal material intersections, such as where drywall is installed against a wall’s top plate—a key checklist item under the new air-sealing requirements.
“We don’t recommend flashing the entire [stud or rafter] cavity with our foam, just the critical joints,” explains Dave Wolf, an Owens Corning product specialist. “We call it ‘critical air-sealing technology.’” Because the foam will seal joints up to a 1/2 inch wide, it offers superior performance where wood movement or shrinking is anticipated, as well as around wall switch and outlet boxes, lighting fixtures, and other penetrations into unconditioned spaces. This system also can be applied without protective gear, and the structure does not have to be isolated during application or curing.
A third type of manufacturer-provided hybrid air-sealing and insulation system recommends using spray foam to completely cover the entire interior side of walls and roofs before batt or blown-in insulation is installed. While these systems tend to be more costly in price and more labor intensive to install, they generally deliver the maximum insulation value possible in a comparable space.
CertainTeed and Johns Manville offer systems that include closed-cell sprayed polyurethane foam, which is applied up to 2 inches in thickness, followed by blown-in insulation and a vapor barrier, when required. Professional installation, the use of installer respirators, area isolation during application and curing, and an investment of as much as $15,000 in equipment are required for these and similar systems.
Installed costs vary widely based on home size, location, and the type of system used, but Robert Brockman of CertainTeed estimates that hybrid flash-and-batt systems for a home with 2x6 wall cavities filled with a 2-inch depth of foam, plus 31/2 inches of blown-in fiberglass insulation and including a vapor barrier (CertainTeed provides an innovative MemBrain vapor retarder that varies in porosity based on ambient heat and humidity), should cost no more than twice the cost of a blown-in blanket system without the foam flashing and two to three times the cost of batt-only insulation. The same hybrid system would cost approximately half as much as entirely filling the 51/2-inch-thick cavities with closed-cell insulating foam.
Although the initial cost of a flash-and-batt application is higher, the improved insulation can result in substantial energy savings over time. According to Brockman, CertainTeed’s hybrid system in a 2x6 cavity adds up to R-28, compared with R-23 with blown-in insulation alone and R-21 with standard high-density batts.
Brockman notes that maximum R-values are not required for all homes, and cost is not always the deciding factor in choosing an insulation system or a reason to use—or not use—a flash-and-batt system.
“It depends on your needs,” he says. “It depends on if you have to exceed codes or if you’re in a certain climate zone. The component parts [of hybrid or flash-and-batt systems] have always been there and available, but our customers are seeking a new pathway to increased performance and energy efficiency. I don’t think there’s going to be a ‘norm’ in terms of insulating systems in homes.”
Going forward, builders may be forced to adopt some form of manufactured hybrid or jobsite-improvised flash-and-batt system to keep pace with ever-evolving air-sealing, insulation, and energy code changes. But choosing the right system will be determined by local code and climate zone requirements, along with cost, availability of trained installers, and other factors.
“Builders are finding these systems to be more effective when used strategically,” says the NAHB’s Wood. “After performance, it comes down to cost and the right product in the right place.”
Michael Morris is a freelance construction writer and EcoHome contributing editor.