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Greatest (new) thing in air sealing?

Andrew C | Posted in Green Building Techniques on

The importance of air sealing is emphasized at every point by GBA and other organizations that use building science for designing (!) and retrofitting residential housing. It is a cornerstone for energy efficiency and for controlling air quality, and also for comfort in buildings. Good air sealing is a prerequisite for using increased amounts of insulation that may reduce energy flow and drying potential in walls and ceilings.

Unfortunately, understanding air leakage and energy flow, ramifications thereof, and learning new building techniques and materials and code requirements (and how to interpret/translate these code requirements for code officials) seems to be foreign territory for a majority of builders and contractors and architects (and code officials), i.e., the professionals that Joe and Jane Public rely on to build and upgrade homes. What a state of affairs. (End of sidebar rant.)

With this as background, I found myself immensely interested in recent news stories about Aeroseal. I’ve been peripherally aware of Aeroseal as a duct sealing tool, but since my ducts have always been inside the building envelope, I’ve been less interested in duct sealing than some people that live farther south. But the concept is great: pressurize the ducts, and then inject an aerosol sealant that flows to leaks and starts sealing them. Air flow is monitored as leaks are sealed, and the process continues until (a desired leakage reduction is achieved). For duct work, 1-2 ounces of sealant is generally sufficient. [This is my summary version of the process.]

Recently I’ve read about the Aeroseal company testing the AeroBarrier aerosolized sealing system that “creates an air barrier around ceilings, walls, floors, doors, windows, and electrical and plumbing fixtures, spraying sealant particles that travel to openings and build up and bond together to seal holes. The firm says the technology can seal gaps up to ½-inch wide and as small as a human hair.” [BuilderOnline, Nov 2017]

And now, an article at JLC [Mar 2018], says that production builder Mandalay Homes has been using the AeroBarrier system “to reliably bring houses down to 0.3 ACH50, time after time.” The description of the process and the results that they’ve had on ~80 houses since July 2017 sounds relatively simple, compared with the heroic efforts most high performance builders use to achieve anything close in sealing performance. Basically, AeroSeal does the same thing as they do for ducts, but they use a blower door to pressurize the house to 100 Pa and then use 6-8 aerosol nozzles to spray sealant throughout the house. The air flow is monitored in real time during the sealing process.

To me, this is revolutionary, with the potential to greatly effect both new builds and perhaps more importantly, retrofits. If the REALIZE group is looking to “adapt the Energiesprong approach to the U.S. housing market” [GBA, 13Mar2018], this seems like a tool to consider.

What’s not to like? Is anyone other than Mandalay Homes testing this system yet? I know it’s early days, but I’m enthusiastic about the idea. What am I overlooking?

P.S. No, I’m not a company employee or shareholder.

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Replies

  1. Doug McEvers | | #1

    Any off gassing issues?

  2. Charlie Sullivan | | #2

    One question would be how well it holds up as things shift, for example with wood dimensions changing with seasonal moisture shifts. But even if the leakage doubles after cracks open up, it's still a lot better than typical construction so maybe it is the right solution for production builders.

  3. Lance Peters | | #3

    I was thinking the same as Charlie - what's the longevity.

    Charlie, while I agree that degradation from 0.3 to 0.6 ACH50 still results in a pretty tight envelope, what I'd be worried about is builders getting used to depending exclusively on this aerosol approach and skipping traditional air sealing techniques.

    With tight traditional construction there are far more small gaps than large ones. If we start leaving houses full of larger and larger gaps the long term durability of the aerosol approach will be more and more in question. I seriously doubt this stuff would hold up as well as traditional tapes and adhesives.

    The other issue I see is where the sealing is done. This process would benefit the house most if done early in construction, sealing the exterior air barrier. If installed after drywall to maximize the effect on electrical and other penetrations in drywall, the exterior barrier could be extremely leaky despite shockingly good blower door test numbers.

    For a custom builder I would think this should be the final step towards getting a house from "very tight" to "better than passive house tight". BUT, I can already hear the wheels turning in the minds of the production builders... "how much money can be saved while meeting minimum requirements?" I can see them pressurizing the house to 50 (instead of 100) and shutting the sprayers down the second the CFMs are below target.

  4. John Clark | | #4

    Your answer can be found here Charlie. Watch out for those joints, and corners, and penetrations !!!

    https://buildingscience.com/documents/building-science-insights/bsi-103-joints-and-corners-and-penetrations

  5. Nick Welch | | #5

    What's the cost? How does that compare to other air sealing methods? Does this company hold a patent on the technique? If it is patented, when does the patent expire? Being stuck with a single vendor increases risk and probably cost, and (probably rightfully) could hinder adoption.

  6. Randy Williams | | #6

    I recently attended a class on Aeroseal, which was presented by the Minnesota Center for Energy and the Environment. They began a research project on the process in August of 2016. Here is a link to the project: https://www.mncee.org/resources/projects/aerosol-sealing-in-residential-new-construction/
    The MNCEE has results similar to the JLC article. The process will work in both retrofit and new construction, though the presenter gave the impression the process works best in new construction. He indicated that using the process with a home that has fiberglass insulation installed and an air leak in the exterior sheathing becomes an issue. Apparently the fiberglass becomes an air filter collecting the sealant before it reaches the leak. It does however work well on the finished side of the envelope. The presenter also said they tested the process against an experienced 3 man weatherization crew, where the crew spent 8 hours air sealing a home. If I remember correctly, there was a reduction of .15 ACH50. That was followed by an application of Aeroseal, which dramatically reduced the ACH50 number. I don't recall the numbers, but I was impressed by the reduction comparison. I actually attended the session with Peter Yost and had the opportunity to ask him a few of the questions similar to the questions on this posting. He indicated the sealant has been around for some time and should durable and work well in this application. I believe it's a water based product, easily cleaned with little or no off gassing once the application is complete. You can enter the home less than an hour after the process is finished. You don't want to be in the home during the process. I've seen cost estimates at around $1000 for the typical home. I am aware of at least one insulating contractor in my area interested in the process. I have a feeling this is going to be the way of the future.

  7. User avatar
    Jon R | | #7

    Would be interesting to know if there is any advantage to positive building pressurization while applying other air sealing. Better to push sealant further into a crack than have air pushing it out.

  8. Andrew C | | #8

    @ Randy Williams,
    Thanks for the your information and for the link. When I followed it, there was another link to a Feb 2018 presentation [Automated House Sealing] that answered a lot more questions for me. 62 pages, a lot of pictures. They detail work done with a variety of builders on both single and multi-family housing, in addition to some commercial work.

    One answer: the sealant is a synthetic acrylic – typically rolled or sprayed on for monolithic exterior air barrier, but diluted for aerosol application. It’s a GREEN Guard Gold Certified sealant for use in California school and healthcare facilities.

    Also, @Nick, it was developed by someone else (Western Cooling Efficiency Center (WCEC) at UC Davis?), and licensed in 2016 by AeroSeal.

    Looks promising to me.

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