Those of you who have been following my blog know I am big on-air sealing. That 10% to 40% of heating and cooling costs are due to air leaks statement I keep talking about. Air sealing does more than save money. Indoor air quality can be improved, building occupants are more comfortable, and durability of the structure is often better.
Air sealing in my northern climate is usually accomplished by installing polyethylene sheeting on the warm in winter side of the framing. Acoustical caulking and adhesive tapes are used to seal the poly to the walls and to itself. Canned spray foam and caulking seal any penetrations between conditioned and unconditioned areas of the home. Gasket materials are used to seal bottom plates and other areas of potential building leakage. Houses I test having this type of air sealing often achieve blower door test results around 2 air changes per hour at 50 pascals, or 2 ACH50. Current building code requires a blower door test result of 3 ACH50 or less.
There are drawbacks to using poly as an air barrier, which I have discussed a few times in this blog. What if there was another way to air seal? There is a new process that is hitting the construction market. I was recently able to watch a demonstration of the technology and attended a seminar at the Energy Design Conference and Expo in Duluth, Minnesota where Ben Schoenbauer with the Center for Energy and Environment gave a presentation on aerosol envelope sealing. MNCEE has been testing aerosol envelope sealing in new construction since 2016 with two Minnesota builders, and according to Mr. Schoenbauer, the results are impressive. The process has reduced blower door test results to well under 1ACH50, and in some cases, under Pausivhaus standards of .6ACH50. An improvement of 60% to 95% in envelope tightness.
According to AeroBarrier, the manufacturer of the aerosol envelope sealing technology, there is a five-step process that the installing contractor follows. Equipment such as a compressor, generator, blower door, emmiters, hoses and the AeroBarrier machine must be first set up. The space it then prepped by covering any areas that won’t be sealed such as plumbing piping and HVAC ductwork. The space is pressurized to 100 pa using the blower door and a computer controls temperature, pressure, humidity, and the delivery of the sealant. The computer displays real-time results showing the improvement of the envelope tightness. Lastly, a blower door test is conducted to confirm the results and a leakage test report is supplied to the contractor/building owner.
The material and technology was founded in 1994 by Dr. Mark Modera, who was a vice president with Carrier Corporation. Aeroseal was originally designed to seal duct work in heating and cooling systems. The process was modified to include building enclosure sealing and recently won the 2018 International Builder’s Show Best in Show and Most Innovative Product awards.
The aerosol sealant is a latex based material that is low VOC and does not off gas. The material is turned into a fog, which is forced through the holes and cracks in the building envelope by using a blower door to induce a positive pressure within the home. A build-up of the latex aerosol seals the air leaks. The product will seal an opening up to 1/2 of an inch. Any larger openings should be addressed before the process begins. The entire sealing process typically takes about four hours to complete. During the seminar, someone asked the question about covering windows and doors. Mr. Schoenbauer replied that the first homes that received the air sealing had the windows covered, which took some time and labor. The windows were not protected in later applications, and no issues were found. All the windows were simply opened after the application to break any sealing from the Aerobarrier process. Mr. Schoenbauer did say that all horizonal surfaces in areas that were finished needed to be covered. For instance, if the plumbing rough-in included an installed bathtub/shower, this would need to be protected. Another question was asked about using the product in an existing home. The process can be completed on existing buildings but is less effective and requires much more prep work. Apparently, fiberglass and loose fill insulation will act as a filter and capture the sealant before it reaches the air leak on insulated exterior walls. The best time to air seal with this product is in new construction after framing and mechanicals are complete, but before the insulation is installed. According to the manufacturer, the air sealing requires application temperatures above 40 degrees. When applying below this temperature, the space will need to be heated.
As for the Aerobarrier demonstration I attended, the experience was well worth the time. I spent about 6 hours with Amit Gupta, the CEO of Aerobarrier along with a couple of their installation techs. Also present was Dave Bohac, P.E., the Director of Research for the Minnesota Center for the Energy and Environment and several contractors and a HERS rater.
A pre-blower door test of the production home being air sealed had over a 3.5 ACH50 at framing and utilities completion. All windows were installed, and polyethylene was installed at the upper level ceiling. Closed cell spray foam was used on the rim joist between the basement and first floor, and first floor and second floor. The larger gaps were all pre-filled with expanding foam. The air sealing process ran for about two and a half hours and reduced the final blower door number to .39 ACH50.
Conducting the final blower door test for the structure was a challenge. After pressurizing the home at 100 Pa for 2.5 hours, the ceiling poly had stretched at the staples. The subsequent negative pressure blower door test pulled a portion of the poly loose. Some new staples and a little duct tape re-sealed the ceiling and a positive pressure blower door test was completed. I think if I where a contractor using the Aerobarrier process for air sealing, I would choose a reinforced poly, or even better, a product like Pro Clima’s Intello for the ceiling. All the photos of the air sealing technology in this blog post were taken at this demonstration.
The rough cost for an Aerobarrier installation is approximately $1 per square foot. This price will vary depending on required tightness level and the amount of prep needed. The cost for traditional air sealing in tapes, gaskets, and caulks along with labor may make Aerobarrier a viable option to air seal a home.
I believe this improvement in air sealing has the potential to change the air sealing industry. My prediction is that because of the time savings, this type of air sealing will become common within the next ten years. Time will tell.