Air Sealing with AeroBarrier

A version of this article appears in the Spring 2019 issue of Home Energy Magazine.

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In many parts of the country, house envelopes are notoriously leaky, with unintended air infiltration that results in additional space-heating and -cooling equipment loads. While voluntary codes and standards for envelope tightness have existed for decades, only recently have these codes become a requirement. Current manual methods for sealing house leaks, even when diligently applied, can fall short of the ultimate tightness goal, due to unrecognized leakage pathways.

The aerosol envelope-sealing technology developed by the Western Cooling Efficiency Center at UC Davis uses an automated approach to produce extremely tight envelopes. The process involves pressurizing the building for an hour or two while applying an aerosol sealant fog to the building interior (see Figure 1). As air escapes the building through leaks in the envelope, the sealant particles are carried to the leaks, where they stick, sealing the leaks. All openings that are not intended to be sealed are blocked with tape, duct mask, or plastic (for example exhaust ducts, door seams, and open plumbing connections). Depending on the condition of the building during application, finished surfaces such as floors and countertops may need to be covered with plastic to protect them from sealant that settles during the process. There is usually no noticeable deposition on vertical surfaces or on the underside of horizontal surfaces. A standard blower door fan is used to pressurize the house, and also provides real-time feedback and a permanent record of the sealing that occurred. The technology is therefore capable of simultaneously measuring, locating, and sealing leaks in a house.

Illustration of AeroBarrier Process

Figure 1. The images in this schematic diagram show the progression of the sealing process from the start (left) to the end (right).

A project funded by DOE Building America is working directly with builders to identify the best stages for incorporating aerosol sealing from the perspectives of cost, performance, and seamless integration into the construction process. The cost of the aerosol sealing and resulting house tightness is being documented and compared to a similar group of houses using conventional sealing methods. In addition to producing tighter houses, conventional sealing methods are being evaluated to determine whether they can be eliminated or reduced to further improve cost-effectiveness. A step-by-step iterative process is being used with builders in Minnesota and California so that lessons learned from the first houses can be applied to later ones.

The process starts with a house leakage assessment that includes a review of the builder’s existing sealing strategies. Then the team works with the builder to determine two promising options as to when in the construction process to apply the aerosol sealing. At least two homes are sealed using each option. Leakage data for the homes sealed with the aerosol approach are compared to data for baseline homes that were sealed under the builder’s standard approach to determine the overall sealing performance. Ultimately, the cost-effectiveness of sealing the homes with the aerosol-based method is compared to the cost-effectiveness of sealing them using conventional sealing methods, based on cost data collected throughout the project. This article describes some of the initial results for this project, focusing on the aerosol-sealing performance with one builder in California and one in Minnesota.

Minnesota House Assessments

The initial house assessments and first round of aerosol sealing have been completed for the builder in Minnesota.

A qualitative assessment of air-sealing details was based on experience from previous work with this builder, and on visual inspections of one house at the rough-in stage of construction and a second house at the predrywall stage. Air sealing was of high quality overall. This qualitative assessment was consistent with the air leakage test results from HERS rater reports of four other houses. The tightness of those houses ranged from 1.2 ACH₅₀ to 1.5 ACH₅₀. The average tightness was 1.31 ACH₅₀ or 56% below the state of Minnesota code requirement of 3.0 ACH₅₀. Since this builder is already achieving house tightness levels well beyond code requirements, the benefit of using aerosol sealing would be to more reliably produce tighter houses and save costs by eliminating some current sealing methods.

Visual inspections determined that half of the air leakage components could have been sealed by the AeroBarrier process. This was based on an understanding of how each building component was currently sealed, whether the component air leaks would be accessible during the AeroBarrier process, and whether the leakage gaps would be small enough to be sealed by the AeroBarrier process. The focus was on components being sealed by caulk or can foam; these components included junction of interior partition wall with exterior wall; sill plate; top plate; electric boxes on exterior walls; and plumbing, piping, and electrical penetrations.

It was proposed to the builder that for half of the houses sealed with AeroBarrier all of the conventional sealing would be performed (Option 1), and for the other half the polyethylene sheets on exterior walls and airtight electric boxes would be eliminated (Option 2). The vapor retarder function of polyethylene sheets would be replaced by low-perm paint on the interior surface of the drywall. Based on the success of an initial demonstration of aerosol sealing, it was decided that AeroBarrier would be applied after the rim joists were spray foamed and prior to drywall. Interior poly sheets were to be caulked and stapled to the second-floor ceilings to create a complete air barrier. Ultimately, the builder was not comfortable with changing the conventional sealing approach, so all homes were sealed under Option 1.

Photos of typical aerosol sealing locations. From the left: vertical gap between framing panels, gap between sheathing and bottom plate, plumbing penetration, and electrical box.

House Sealing with AeroBarrier

In the fall of 2017, four houses in the Twin Cities metropolitan area were sealed by AeroBarrier for the first builder. The two houses in Blaine and Eagan were aerosol sealed prior to wall insulation. The starting envelope leakages were 3.81 ACH₅₀ and 3.78 ACH₅₀ respectively, and those were reduced by 72% and 82% to 1.05 ACH₅₀ and 0.67 ACH₅₀ respectively (see Figure 2). The electric wire and most plumbing penetrations from the house to the attic would typically be sealed with can foam. Can foam sealing was not performed for the Blaine house prior to the aerosol sealing. When can foam was subsequently used to seal the electrical and plumbing penetrations to the attic, house leakage decreased by only 15 CFM₅₀. That indicates that the aerosol sealing effectively sealed electrical and plumbing penetrations. In addition, the gaps between the sheathing and the top plate, the sheathing and the bottom plate, the bottom plate and the subfloor, and the vertical gap between framing panels were sealed effectively using AeroBarrier. While these gaps were typically narrow, there are hundreds of feet of these gaps in each house, which suggests that the total leakage area could be significant.

Batt insulation had been installed in the exterior walls of the Plymouth and Lakeville houses, which the project team had not anticipated. The team removed much of the insulation from the Lakeville house prior to aerosol sealing, and portions were removed from the Plymouth house. The wall insulation resulted in longer sealing times and leakier houses. The Plymouth and Lakeville houses started with leakages of 2.87 ACH₅₀ and 2.82 ACH₅₀, respectively, and those were reduced by 46% and 66% to 1.55 ACH₅₀ and 0.97 ACH₅₀, respectively. It is evident that the wall insulation acts as a filter for the aerosol sealant and should not be in place over any potential leakage areas. In addition, the poly sheets on the ceiling came loose at two of the houses. The process of securing the sheets needs to be more robust. Finally, the air compressors used for the sprayers malfunctioned in three of the houses, which reduced the number of sprayers and extended the sealing times.

Air-Sealing Tests

While there were numerous minor glitches in the sealing process, the tightness of the four houses was significantly reduced compared to the baseline homes. This was achieved prior to the installation of the interior poly sheets over the exterior walls and sealing of the electric boxes—indicating that the required house tightness can be achieved without the interior poly, with the application of low-perm paint, satisfying the vapor barrier code requirement. This builder did not eliminate any of its sealing practices for these four houses, but it has tentatively agreed not to use interior poly on exterior walls for the second round of houses (as long as the local code officials approve of this application).

The house assessments and air leakage tests were repeated at the end of construction (green bars in Figure 2). The garage of the fourth house was being transformed into a sales office. It was not possible to measure the air leakage of the house without including that area, and the garage had not been included in the pre- and postsealing leakage measurements. For the two houses that were sealed when wall insulation was not present (Blaine and Eagan), the leakage rate was decreased by 14% and increased by 37% respectively between the aerosol sealing and the end of construction. An infrared and visual leak inspection did not identify any large leaks to explain the increase in leakage (from 409 CFM₅₀ to 560 CFM₅₀) for the Eagan house. For the Plymouth house, which had wall insulation in place at the time of sealing, the air leakage at the end of construction was 47% lower than the leakage measured after sealing; that was anticipated, since it appeared that the wall insulation was filtering the movement of sealant to leaks at the exterior walls. At the end of construction, three of the houses with AeroBarrier sealing were 39–45% tighter than the two control houses, which were not sealed with AeroBarrier.

Summary of Results in Minnesota

Figure 2. Presealing, postsealing, and end of construction envelope air leakage test results for four sealed and two control houses.

California Houses Get Tightened, Too

The project team conducted a visual inspection of four homes in California. These homes were under various stages of construction, from the point when exterior sheathing was installed to the drywall stage. The inspections, which were based on the Energy Star Rater checklist for building air sealing, showed a high quality of air sealing. The homes were designed with sealed attics and used open-cell spray foam at the rim joist and under the roof deck to both insulate and provide air sealing. After the initial assessment, the project team met with the builder and determined two options for applying the aerosol sealing. Four homes were sealed, two using Option 1 and two using Option 2 (described below). The homes were all two stories, designed with a sealed attic, and ranged in size from 2,030 to 2,570 square feet.

Option 1

AeroBarrier sealing for Option 1 occurred after open-cell spray foam was installed at the rim joist and below the roof deck. No additional sealing was performed prior to the AeroBarrier installation. The presealing results showed air leakage of 4.39 ACH₅₀ and 3.47 ACH₅₀ respectively for the two homes during this stage of construction.

Open-cell spray foam installed below roof deck in the home sealed under Option 1.

The AeroBarrier sealing was very successful. The overall time to seal each home, including prep and cleanup, was about three hours. The leakage at the start of the sealing was 1,200–1,500 CFM₅₀. Figure 3 shows the sealing profile for both sealing demonstrations under Option 1. There were slight differences in the time required for sealing and in the starting leakage rate, which is likely due to differences in the floor plan for the homes. In both cases the AeroBarrier sealing reduced the leakage by about 75%, bringing the leakage rates down to 1.11 ACH₅₀ and 0.95 ACH₅₀, respectively.

Sealing Profiles after Spray Foam

Figure 3. Sealing profile for both houses under Option 1.

Option 2

For Option 2, the AeroBarrier sealing occurred before open-cell spray foam was installed. This represents the first opportunity to seal the homes, since the building shell is largely complete. Some manual sealing prior to installing AeroBarrier was required to block larger penetrations that would not have been sealed efficiently with the aerosol. The time and materials required to perform that sealing were documented. There were also some issues coordinating the sealing demonstrations with the home builder; this led to some gaps remaining at the eaves of the home that would normally have been blocked prior to the AeroBarrier installation.

Besides the additional sealing at the eaves, there was also manual sealing of other large penetrations. In the first house the presealing effort was focused on penetrations that would clearly not seal appropriately with the aerosol technology, while in the second house more care was taken to seal gaps that were easily identifiable, because they let in the daylight. The time required and materials used to seal large gaps prior to sealing under Option 2 are outlined in Table 1.

Table 1. Time and Materials Used to Manually Seal Homes Prior to AeroBarrier Installation in California

After the two presealing efforts under Option 2, leakage was 15.1 ACH₅₀ and 9.0 ACH₅₀ for lots 23 and 24 respectively. Clearly the additional manual sealing effort resulted in improved initial airtightness but at an increased cost. Ultimately, the results obtained with the additional manual sealing will need to be compared to the results obtained with AeroBarrier sealing alone, to determine whether the difference in performance justifies the additional cost.

An uninsulated and exposed rim joist in the house sealed in Option 2.

The AeroBarrier sealing was also very successful at this stage of construction. The sealing injection time increased from the sealing under Option 1, requiring two to three hours to complete. The overall time to seal each home, including prep and cleanup, was about four or five hours. Due to slight changes in the manual presealing efforts in each building, the leakage at the start of the sealing was around 5,800 CFM₅₀ in one case, and about 3,000 CFM₅₀ in the other. Figure 4 shows the sealing profile for both sealing demonstrations under Option 2. The sealing was faster at the beginning of the installation and slowed as the process continued. The AeroBarrier sealing reduced the leakage in both cases by about 85%, bringing it down to 2.15 ACH₅₀ and 1.43 ACH₅₀ respectively before spray foam installation was installed.

Another leakage test on each home was performed after the spray foam installation to determine how much additional sealing was required due to the insulation. After spray foam, the measured air leakage of the homes was 1.25 ACH₅₀, and 1.06 ACH₅₀, representing an additional leakage reduction of 6% and 4% respectively, relative to the initial leakage of the homes. This result is only slightly higher than the result for using AeroBarrier after the spray foam installation under Option 1.

Sealing Profiles before Spray Foam

Figure 4. Sealing profile for both houses sealed under Option 2.

Table 2 and Figure 5 provide a summary of all of the AeroBarrier sealing results for the first round of tests for the homes in Lodi, California. Overall, nearly 10,000 CFM₅₀ of air leakage was sealed in eight hours of total injection time over two days. The average airtightness achieved was 1.09 ACH₅₀ before drywall was installed in the homes. Final air leakage tests performed after the end of construction showed very little change in air leakage (an average of 1.12 ACH₅₀).

Table 2. Summary of AeroBarrier Sealing Results

Summary of Results in California

Figure 5. Air leakage results summary for all homes at each stage of the process.

Conclusions

The AeroBarrier installations were all very effective at sealing air leaks in the homes. The average tightness achieved was below 1 ACH₅₀, which is well below the relevant code requirements in both Minnesota and California. Furthermore, the air leakage was assessed prior to completion of the homes, and in many cases prior to drywall installation. This project demonstrated the ability to seal homes at various stages of construction, including before and after drywall is installed, allowing the process to be applied in many different situations.

The four houses sealed for the Minnesota builder had an average air leakage of 0.98 ACH₅₀ after sealing and before the polyethylene sheet and drywall were installed. That is 50% tighter than the average leakage of the two control houses at the end of construction. This indicates that the required house tightness can be achieved without the interior poly, with the application of low-perm paint satisfying the vapor barrier code requirement. Eliminating the poly sheeting and airtight electrical boxes, along with increased utility incentives, may more than offset the added cost of the AeroBarrier sealing. The authors plan to conduct a comprehensive analysis of the cost tradeoffs in the future.

For the California sealed-attic homes, sealing with AeroBarrier produced tight houses when it was done either before or after the spray foam was applied under the roof deck. However, sealing with AeroBarrier before insulation could allow the builder to use less-expensive alternatives to insulate homes. The overall cost savings of alternative insulation methods will determine which option should be pursued in the future.

The AeroBarrier process not only produced tight homes but also demonstrated a potential opportunity to reduce manual sealing efforts in new construction. A review of the standard air-sealing efforts performed by builders in the United States shows several areas where manual sealing efforts can be reduced or eliminated when applying AeroBarrier. The project team will collect and evaluate cost data to determine the potential cost savings of using AeroBarrier in place of other manual sealing efforts.

Curtis Harrington is a senior engineer at the UC Davis Western Cooling Efficiency Center, where he manages research projects on a variety of topics, including evaporative cooling technologies, aerosol-based sealing methods, and building energy modeling. Dave Bohac is the director of research at the Center for Energy and Environment in Minneapolis.

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