Air sealing is generally considered one of the most cost-effective ways to reduce energy use in buildings. That’s why advanced air sealing is an essential element of zero energy homes. As ever more sophisticated means of plugging leaks have been applied, the air leakage rates of new homes have slowly, but consistently declined. A decade ago, a typical mass-produced home might have an air leakage rate of 8 to 10 air changes per hour at 50 Pascals (ACH50). Today, the leakage of a typical new home may be down to 4 or 5 ACH50. Most zero energy homes push the leakage rate to 1.0 or 2.0, while Passive House requirements allow a maximum leakage of 0.6 ACH50.

A builder once called tracking down air leaks “death by a thousand cuts.” Large gaps, such as that huge hole in the floor sheathing that plumbers cut below the tub, are easy to see and address. But, it’s the tiny cracks and gaps—some too small to see—that increase cost and tax patience. The process has been somewhat subjective and uncertain. Even after hours of work it can be difficult to determine the actual air leakage rate until the building is tested.

A Game Changer?

There’s a new approach that may change the nature of the air sealing process and transform it from an art to a science. Aerobarrier is an aerosol sealant that fills all gaps less than ½-inch in just a few hours. The process uses a blower door to pressurize the building and automated sprayers to create a fog of acrylic sealant inside the building. As this fog travels along the air leakage pathways, it passes through the gaps in the building envelope, where it accumulates on the edges of the openings. After a few hours, the sealant fills all the gaps. Best of all, you can dial in a specific level of air tightness to meet a specific energy performance goal.

How it Works

A blower door is used to pressure the building, forcing Aerobarrier sealant into gaps and openings.

Preparation includes what you might call gross or large scale air sealing. This includes blocking that hole under the tub, covering open wall cavities behind fireplaces, all the typical fire caulking around pipes and wires, etc. But any remaining gaps less than ½-inch can be skipped.

Then, the construction sequence must progress to a stage where the building can be pressurized. The easiest stage in a normal construction schedule would be after drywall has been installed. While the sealant will not accumulate on vertical surfaces, it’s still necessary to cover windows, exhaust fans, and duct registers.

Equipment setup involves mixing the acrylic sealant and setting up the pump and blower door for building pressurization. Several aerosol spray heads are placed around the building. The blower door runs to maintain the building at 100 Pascals of positive pressure while the sealant is sprayed into the air. Most homes require three to four hours to reach the targeted level of tightness. Tighter results require more time. A computer controls the process and monitors air leakage, so the operator can stop when the desired level of air leakage is reached.

Because the official building air leakage is measured using building depressurization, the blower door fan must be reversed to document the final air leakage rate.

The cured sealant does not emit volatile organic compounds into the finished home. However, it’s hazardous to enter the building during the operation without a full face respirator and outside air supply due to the danger of breathing aerosols. The sealant is Greenguard Gold certified for low toxicity. The sealant is ultra-low VOC with no off-gassing and it has no Red List items, so it is safe to use inside the house.

Cost

Aerobarrier is licensed to local operators, who set their own prices. Two factors affect the total cost: level of air tightness and building size. High volume builders may get better prices. Depending on these factors, it might cost $0.80 to $3.00 per square foot. Be sure to check with a local installer for pricing in your area.

Advantages

Aerobarrier offers advantages to every building project where air sealing is a priority. The system reduces headaches for builders and speeds construction. While gross sealing measures, such as fire caulking, large penetrations and hidden air barriers, are still required,   the final responsibility is assigned to one subcontractor who can dial in a specific leakage rate in less than one day. In the past, air sealing activities would span virtually every stage of construction, but the result wouldn’t be known until the building was complete and corrections would then be difficult to make.

Consistency is a another benefit, especially for high-volume builders for whom an air tightness level of 3.0 ACH50 has become a common target for building science or for economic reasons. With Aerobarrier it’s easy to hit this target in every home. This consistency is valuable for designing appropriate ventilation systems, which should complement building leakage. The system works just as well with complex architecture as it does with simple designs. In either case, Aerobarrier takes the stress and uncertainty out of the air sealing process.

One additional advantage – depending on the project – is cost. If a builder’s current practice requires a few cases of caulk and a couple of days of labor, then their current practice may be less expensive than Aerobarrier, which may cost several thousand dollars to bring a typical home to a typical level of tightness. On the other hand, super air sealing at 2.0 ACH50 or below requires more time, materials, and supervision of multiple tradespeople. And often it requires additional sealing after the blower door test is run. Aerobarrier could well be less expensive than these more sophisticated options. Many builders use proprietary air sealing wraps, sheathing or fluid applications, which have their own costs. The final analysis will depend on the specific circumstances of the job.

Perhaps the biggest advantage to using Aerobarrier would be in existing homes where many leakage sites are simply inaccessible without major demolition. In this situation, Aerobarrier can achieve far greater levels of air tightness. The process here would be similar to spray painting the interior, involving moving furniture and masking windows, etc.

History

The idea behind Aerobarrier isn’t new. The concept, originally called Aeroseal, was developed in 1994 by Dr. Mark Modera at Lawrence Berkeley National Laboratory. HVAC contractors began using the Aeroseal system on heating and cooling ducts in the field in 1997. Over time, the concept was adapted to entire buildings and in late 2017, Aerobarrier was introduced at the International Builders Show.

Will Aerobarrier revolutionize building air sealing? If you have thoughts, please share them in the comments section below.