Air seal needed at eave prior to AeroBarrier process. Photo courtesy of U.C. Davis Western Cooling Efficiency Center.Thermal bypass rough cut insulation and perimeter spray foam sealed prior to AeroBarrier process. Photo courtesy of U.C. Davis Western Cooling Efficiency Center.You can use AeroBarrier before cavity insulation is installed (essentially completing an exterior air barrier) or after drywall (essentially completing an interior air barrier); in either case requiring pretty limited protection of finished surfaces.The real beauty to me of the AeroBarrier approach is that it is real-time performance-based. The blower door testing and results is built into the AeroBarrier process.AeroBarrier in existing buildingsIf an existing building is between occupants, there will be protection of more finished surfaces required—and the bigger thermal bypasses still need to be at least “rough” sealed—but that does not seem like that much of a jump from AeroBarrier post-drywall in new construction.Paul Springer, manager of business development for AeroBarrier, connected me to Mitchell Spence of Redfish Builders, the leading AeroBarrier partner doing existing homes. Springer stated that about 10% of the AeroBarrier partners nationwide work on existing buildings but they do this completely on their own. Springer also noted: “We do have a new grant from the DOE in which we are going to be applying AeroBarrier in finished spaces (non-occupied) to understand the benefits.”“About 10% of our air sealing business currently is AeroBarrier in existing homes,” says Spence. “The key for us managing the liability of damage to contents is our partnership with a painting company. They know how to rigorously and efficiently seal everything from clothing to furniture to floor coverings and we know how to seal the building.”Spence feels the other key to his AeroBarrier work is his background in high performance building at Redfish. It’s his knowledge of the building process and business partnerships with trade contractors and other builders that means AeroBarrier work on new production homes, new custom homes, existing homes, and multi-family projects.Spence has tuned his air sealing of existing buildings with AeroBarrier. “I pretty routinely suit up with respiratory protection to first target my Retrotec fogger at suspected leaky areas and then relocate the AeroBarrier spray heads to target those leaks. I also use “first sweep” during AeroBarrier air sealing, brushing off aerosol that is going after surface leaks encouraging aerosol sealing a bit deeper into existing building assemblies.” Spence also noted that quite a bit of the prep for holes and cracks larger than ½-inch gets addressed with closed-cell backer rod, which costs about $100 for a 500 foot roll off of Amazon.The following images are various types of prep completed by Mitchell Spence’s painting contractor in occupied existing projects.Painter prep in rec room Photo: Mitchell SpenceNote how the carpet has been pulled back from exterior walls and the bed fully sealed. Photo: Mitchell SpenceSealing off all fixtures in a bathroom. Photo: Mitchell SpenceMasking off kitchen appliances and cabinetry. Photo from CEE report: Using and Aerosol Sealant to Reduce Multifamily Envelope Leakage.Spence is a big advocate of AeroBarrier for multi-family air sealing. “We can do unit-by-unit AeroBarrier work, not only sealing the building enclosure but between units. This has big indoor air quality and sound transmission benefits,” says Spence.Using two duct blaster fans to pressurize an existing MF unit to 100 Pa for AeroBarrier air sealing. Photo from CEE report: Using and Aerosol Sealant to Reduce Multifamily Envelope Leakage.From early work on aerosol sealing of multi-family units comparing the labor for new construction, existing, and existing occupied. Chart from CEE report: Using and Aerosol Sealant to Reduce Multifamily Envelope Leakage.Tested results. Chart from CEE report: Using and Aerosol Sealant to Reduce Multifamily Envelope Leakage.How AeroBarrier in existing buildings could be a game changerIncreasingly, as I do assessments and investigations of existing buildings, performance concerns of the building owners are rooted in air leakage, from comfort complaints to more serious moisture issues. And those same clients often have questions and concerns regarding spray foam as pretty much the only game in town for seriously improving the airtightness of existing buildings.I think that AeroBarrier in existing buildings can give spray foam a real run for its money in many of the 100+ million existing dwelling units we have in the US. An aggressive and elastic yet largely benign acrylic aerosol (see AeroBarrier MSDS) could be just what our existing building stock needs to safely improve the toughest aspect of existing building performance: airtightness.But how much does it cost?Spence told me that for occupied homes AeroBarrier runs between $3 and $4.25 per square foot of building but it makes a big difference what type of building. “Large custom homes can be up to $7 per square foot including both prep and AeroBarrier process,” says Spence.What do you think?Peter Yost is GBA’s technical director. He is also the founder of a consulting company in Brattleboro, Vermont, called Building-Wright. He routinely consults on the design and construction of both new homes and retrofit projects. He has been building, researching, teaching, writing, and consulting on high-performance homes for more than twenty years, and he’s been recognized as NAHB Educator of the Year. Do you have a building science puzzle? Contact Pete here. AeroBarrier has been in the building news quite a bit lately:GBA – Aeroseal rolls out air sealing technology for houses Fine Homebuilding – New technology improves airtightnessJournal of Light Construction – A game-changer for airtight constructionHow AeroBarrier WorksAeroBarrier is an innovative and sophisticated system for air sealing buildings. During installation, a proprietary synthetic acrylic is aerosolized while the home is under pressure developed by a blower door. As the air leaks through the building enclosure, the latex aerosol sticks and builds up on pretty much any crack up to about ½-inch.AeroBarrier is installed using a system of equipment seen here in a fully outfitted construction trailer. Photo courtesy of AeroBarrier.During installation, the AeroBarrier system is controlled by software that keeps track of blower door pressure, pressure delivered at aerosol heads, temperature, and relative humidity inside and outside the building. Photo courtesy of AeroBarrier.AeroBarrier aerosol head fired up to seal leaks using positive pressure delivered by blower door. Photo courtesy of AeroBarrier.Blower door outfitted with an inline heater to ensure that proper temperature is maintained inside the building during the air sealing aerosol process. Photo courtesy of AeroBarrier.In this AeroBarrier project, an exterior 6-inch exhaust duct was outfitted with a taped-in mesh to show how the aerosol fills in and seals. Photo courtesy of AeroBarrier.The mesh sealed after AeroBarrier installation. Photo courtesy of AeroBarrier.In under 2 hours, a home can move from leaky to pretty much whatever level of air sealing you are prepared to pay for.You do, of course, need to prep the building, air sealing pathways larger than ½-inch, but following the Energy Star Thermal Bypass Checklist heavy hitters is straightforward.