What Is Aeroseal and Do I Need It?

By Buz Artiano, BuildX | October 2025

Every Massachusetts ADU builder eventually comes across this issue: the framing looks perfect, the insulation is installed correctly, and then when the energy rater shows up for the blower door test, the house is still leaking too much air. We go through and find every gap and seal them with caulk guns and foam cans, but these invisible punctures from electrical and other things just keep leaking air.

At BuildX, out of all the ADUs we have built here in Massachusetts, we have never failed a blower door test. Our projects end up coming in around 1.0 ACH50, the minimum requirement is 1.5. On a project we just did in Marshfield on the water, we hit 0.7 ACH50 when we only needed that 1.5. Getting that tight of a seal takes obsessive attention to detail during framing, but even then, there can be invisible gaps that constantly leak air. So that's why we started using Aeroseal technology.

How Does Aeroseal Work?

Think of Aeroseal as Fix-a-Flat for your ADU envelope. Instead of running around and looking for invisible leaks with a caulk gun, you can just seal everything at once from inside the house.

The whole thing works by using pressure. We install a blower door and pressurize the ADU to 100 to 200 Pascals, which by the way is 2 to 4 times the pressure they use for a standard blower door test to make sure you're up to code. Then we spray the aerosolized acrylic sealant into the space. The fog naturally floats toward any air leak and deposits sealant particles that build up and seal gaps automatically.

The sealant is water-based with no harmful VOCs. It dries within an hour and is completely inert with no off-gassing after that. Aeroseal is UL GreenGuard Gold certified, which means it holds up to the highest standards they use for hospitals, schools, and houses where air quality is a big deal.

We can watch the sealing happen in real time. The system plots CFM reduction every 60 seconds, so we know exactly when everything is officially air tight. At the end, we get a document that shows the starting and ending air leakage, duration, sealant used, and percentage of air reduction so you can see the proof.

What Results Can You Expect?

The performance improvement from Aeroseal is absolutely undeniable. Here are some real numbers from some of our BuildX ADU projects:

We just used Aeroseal on one of our projects in Falmouth, and it took the ADU from 1.6 to 1.7 ACH50 down to 0.7 to 0.85 ACH50 only using about a gallon of sealant and in only two hours. You can't get that kind of improvement by manually sealing.

What Does the Installation Process Look Like?

The prep work is what takes the most time when we do an Aeroseal application. The actual sealing only runs a few hours at the most.

Before the Aeroseal team arrives:

• Remove all tools and materials from the space
• Clear full access to the exterior envelope
• Make sure your electricians have prepped their wires but that they have not installed any actual devices

We have to work with a clean job site because as the house gets tighter, the sealant has nowhere to escape so it washes back into the house. Anything left in the space will get a thin coating of sealant mist.

Timing in your build schedule:

We schedule Aeroseal after the plaster is hung and we finish before the final touches. This way you know the envelope is tight. In the future if there are any other punctures, such as a plumber drilling a new hole or an electrician pulling wires, they will be easy to find and fix.

Aeroseal can seal gaps up to about 5/8 of an inch. If you can see a gap, you always want to seal it manually first. Aeroseal is more for the penetrations you don't see. And those are the biggest culprits for air leakage anyway.

What Are the Costs and Payback?

Aeroseal pricing typically runs $1.00 to $1.50 per square foot, which usually ends up being $3,500 to $5,000 for an average 900 square foot ADU. But it pays for itself in more than one way:

Pay special attention to those HVAC downsizing numbers. A better envelope means your heat pump isn't working as hard, which a lot of times means you can go with a smaller system. That money can go right towards the Aeroseal to offset the extra cost.

Why Is Aeroseal Critical for Heat Pump Performance?

If you switch to an all-electric home without making sure the building has a good seal, it will be difficult to heat it efficiently and your electric bills go way up.

Heat pumps work differently than normal fuel systems. They put out heat at lower temperatures over longer periods of time. In a house that's full of leaks, all that slowly temperature controlled air escapes right back out through gaps, which then makes the system have to run non-stop. Even if your heat pump is rated for negative 15 degrees, in a leaky house, if it's zero degrees you'll still be cold because the system can't keep up with all the heat loss.

We control the air movement, seal leaks, and make sure the system doesn't have to work so hard. Winter air stays warmer coming in. Summer air stays cooler. Your ADU becomes much more efficient overall.

When Might You Not Need Aeroseal?

We use Aeroseal on most of our projects, but it's definitely not a requirement.

If your ADU gets as tight a seal as you want through careful manual sealing during framing, then you don't need to spend the extra money on the Aeroseal. Our track record shows we can do that. We regularly hit 1.0 ACH50 just by being thorough at bottom plates, top plates, rough openings, and penetrations.

However, you do need Aeroseal in some situations:

• When you're trying to get to HERS 42 ratings or even better for passive house standards requiring 0.5 to 0.6 ACH50
• When complicated geometry causes lots of holes you can't see
• When there's not enough time to go through and do all the meticulous sealing
• When you need guaranteed blower door test results without any risk of having to call us back

For homes that need an extra tight seal, we will often combine spray foam insulation with Aeroseal to reach 0.5 ACH50 targets.

How Long Does Aeroseal Last?

The sealant has been through lab testing with approximately 50 years of guaranteed results. We've been using it since 2017 and 2018, but there are other duct sealing products that have held up for decades as well.

The acrylic sealant can accommodate normal building movement without cracking or separating. Assuming no one drills new holes through your envelope after application, the seal will stay there forever.

Guarantee Your ADU's Energy Performance

A tight building envelope is the basis for an energy efficient ADU. It affects comfort, energy bills, and how well every mechanical system in the building works.

At BuildX, we work with certified Aeroseal contractors to make sure your ADU meets the strict air-sealing goals. Whether you need guaranteed blower door results, heat pump optimization, or net-zero performance, our team can help you decide whether Aeroseal makes sense for your project.