What Is AeroBarrier Air Sealing and Should Your ADU Builder Use It?

By Buz Artiano, BuildX | September 2026

Watch: Your House Is Leaking, Here's How to Seal It Right w/ Alex MacLean | BuildX Podcast #07

Somewhere in the estimate for your ADU, a line for aerosolized air sealing is either there or it's not. If it's there, it seems like something no one talked about during design, and there's a cost connected to it you didn't budget for. If it isn't you have no way to tell whether your builder is dealing with air tightness another way or is just hoping that the finished ADU will test where it should. Either way, you're being asked to approve something you haven't any way to evaluate.

My name is Buz Artiano, and I am the founder of BuildX. We've built dozens of ADU projects across Massachusetts, mostly around the South Shore and Plymouth County areas. We are the only team you need: we do the design, permitting, and construction. So we see every phase of a project from the first site visit up until you move in. We evaluate septic constraints, zoning issues, utility connections and the requirements for a permit from the city. That means we deal with everything on a project including the by-right review by the town, and the energy code verification at the end that decides whether anyone gets a certificate of occupancy. Massachusetts allows one accessory dwelling unit by right in single family zoning areas, although municipal building code, health code, and dimensional requirements still apply to every project. You can review the state requirements at mass.gov.

When the Massachusetts energy code tightened, we told the whole company to make aerosolized envelope sealing standard on BuildX builds instead of making it an upgrade that the client has to request. That decision came from seeing what the tested air tightness number does to a building finished the old way. You don't need to be an expert in any of this to make a good decision. You just need to know if the line item is real, what it should cost, and what to ask about when it's not there.

What Is AeroBarrier Air Sealing and How Does It Work?

AeroBarrier is a waterborne acrylic sealant that's in aerosol form and is fogged into a building while the building is held under pressure. The pressure is what does the work. Alex MacLean, the Northeast account manager for Aeroseal who talked to us on episode 7 of the podcast, said that it's "just kind of like fix-a-flat for a tire." Air escaping through the structure takes the sealant with it, and that sealant collects at the openings and closes them from the inside out.

The pressure is higher than most homeowners would guess. A standard multipoint blower door test depressurizes a house to 50 Pascals. A sealing pass runs the building at 100 to 200 Pascals, which is two to four times that, because the crew wants every leak to be moving air. Software maps the reduction of the leakage live, either at the instant it happens or every 60 seconds so the number goes down while the work is happening instead of showing up as a surprise at the end.

The system will close a gap up to about half an inch to five eighths of an inch. Anything bigger than that and anything you can actually see has to be closed by hand first. The material itself is very low in volatile organic compounds, which are the chemicals that come off as gas from the building products into the air you breathe. Alex said the product is UL GREENGUARD Gold certified, a certificate worth checking against the Aeroseal documents. Re-entering the house after it has been fogged takes 20 minutes to an hour.

There's one honest limitation about the life of the product. The 50-year figure comes from simulated lab testing, not from actual use in the field. The material has only been used in real buildings since 2017 or 2018. The closest thing to a record of its performance is a duct sealing version of it that's been used for about 20 years and was still sealing where inspectors have looked at it.

The equipment that it takes is smaller than most people expect. A crew brings:

• Seal stations that are about the size of a travel case, every one with their own pump and humidity and temperature sensors
• A two and a half gallon sealant pail put into each station
• A mesh wireless network that connects every station to a laptop or a central control unit

Why Is Your Builder Bringing This Up Now?

The Massachusetts energy code changed, and that change took air tightness from something builders dealt with to something a rater measures and files. Massachusetts has three levels of residential energy code: a base code that applies everywhere, an opt-in Stretch Code, and an opt-in Specialized Code. It's up to your town which one is over your ADU. You can check your town's level and read the current code documents at mass.gov.

This is what it means for you. The HERS rater, not your builder and not us, decides the air tightness number that your plan has to have. HERS stands for Home Energy Rating System, and the rater is the independent third party who checks your walls, windows, ceiling assembly, and mechanical equipment, and then does the final blower door test that either approves your ADU or doesn't. There isn't a single standard in Massachusetts that every ADU has to meet. There's a number that comes from your plans which means it can be dealt with early, before the framing starts.

When the code changed, we made this a decision for the entire company instead of having it depend on each project. Every BuildX ADU now has aerosolized sealing in the specifications. The reason for that isn't complicated. Not doing it saves a few thousand dollars only when the finished ADU tests where it's supposed to on the first try, and taking a chance on a certificate just to save four thousand dollars is too risky, and we stopped doing that.

So if the spec sheet you are looking at doesn't have a line for air sealing and no other way for getting to the tested number, you shouldn't accuse but should definitely ask questions. There are legitimate answers a builder could give you and they're worth knowing before you ask.

What Does AeroBarrier Cost, and What Drives the Number?

Three things will change the price. The first is the square footage, because the work is quoted to cover the conditioned area of the building. The second is volume, and that means if the person who is installing the barrier is giving the price for one ADU or for a builder who sends them projects all the time. The third is the preparation because the longest part of the day isn't spraying it's covering ductwork, pulling material out of the building, and getting the outside ready to hold pressure. Pricing is based on the drawings with a fast turnaround, and it will be accurate as long as square footage and volume in the time between to quote and the actual build.

The number per square-foot buys the sealing pass and the certificate that you get with it. It doesn't pay for your insulation package, or the HERS rater's modeling or the final blower door test. It also doesn't pay for hand sealing of any of the large openings that the system can't close. Those are separate things done by different people, and a builder who lumps them together is making your estimate harder to figure out, not easier.

With those things on the table, here's what the prices are based on our conversation with Aeroseal. These are just price ranges for general construction, not a quote for any particular building.

If you use those figures for the entire ADU it will come out something like this: a 3,000 square foot house will cost about $3,000 to $4,000 added to the total project. On an ADU the dollar cost is smaller, and it's one of the smallest line items and also one of the few that directly decides if the ADU can be lived in.

When Does AeroBarrier Go In on an ADU Build?

The outside has to be finished and it must be able to hold pressure. That means weathertight with windows installed, insulation done complete, and every penetration through the shell already finished. Before the truck comes, this list should be completed:

• Electrical and low-voltage wires put through the shell and terminated
• Plumbing lines and sill cocks run out through the exterior
• Hood vents, dryer vents, and bath fan vents cut in
• ERV or HRV duct penetrations cut through, even when the unit is not online yet

The order of the insulation will decide the rest. If the ceiling is getting insulation under a vented attic, then the sheetrock has to be put up first so it has an outside to pressurize. And the builder has to take out the tools, stored material and anything that doesn't stay. The reason isn't tidiness, it's because as the building gets sealed tighter and the air fills with the sealant you get a wind blowing effect inside. So just covering something with plastic doesn't work. Things have to be taped and covered.

We schedule this using a check list, not just the calendar and that's where most builders lose money on it. Every trade that causes leaks each work on their own timetable and the sealing crew can't start until the last one is finished. So we call the installer before the frame goes up, let them know when we need the work done and then hold the other trades to that milestone. On the Falmouth project we called ahead and told them exactly when we wanted them, and that took a single visit. That scheduling decision can help make a job take only half a day with no mess, and it costs nothing except knowing to make it early in the process.

The Proof You Receive When the Sealing Crew Leaves

The crew leaves you a seal certificate that shows the leakage number when they started, the number when they finished, how long it took and how much sealant they used, and the air reduction percentage they got. That's the document you can give to a lender, to your rater, or to a buyer later on, and it's the reason this line item gives you something you can hang on to instead of something you have to just take on faith.

The crew also pushes the number over the target on purpose. If a rater puts the target at one and a half air changes, the crew takes the building to and a quarter or to one. The difference between the target and the final number is a planned safety factor and it's there to take care of everything that happens on the job after they leave.

We used the system for the first time about a year and a half ago on a project in Falmouth. The building started around 2.1 air changes. We asked them to bring it down near 0.85, because we wanted to end up at one or under. The final blower door test came in around 0.95. Those figures are what we remember about the job rather than readings from a certificate, so think of them as an estimate.

What impressed us more than the number was what the process left behind, which was nothing. There was no cleanup, no residue, and nothing was damaged. Alex says the normal worst case is a slightly sticky floor that will be swept with the rest of the construction dust and debris. On our build, we knew it had happened but we couldn't find any visible evidence of it.

What Should You Ask Before Anyone Fogs Your ADU?

Ask how many of these procedures the crew you have has actually done. It's a new trade and Alex says that about 90 percent of the contractors that call Aeroseal are doing their first job with it. Experience matters here because an experienced crew understands leakage numbers and knows what a sudden spike means because they've seen it before and know what causes it. We don't want on-the-job training on our buildings, and you shouldn't want it on yours.

When something does go wrong, the cause is operator error instead of a failure of the product. A nozzle might be pointed directly at a wall surface, or someone bumps a station walking past it. The fix is cosmetic and repairable: some plaster is replaced. That's about the worst that will happen and it's a big part of why we're comfortable putting this in every specification.

Nobody can be in the building during the spray. The material is airborne by design and you don't want it in your lungs. If you come in during the process you will need a full-face respirator, which is the installer's equipment and the installer's responsibility, not yours. Half an hour after the fog settles, the space is walkable again.

Three questions worth putting to any builder or installer before the work is scheduled:

• How many of these installs has the crew on my job actually done?
• During what part of my schedule are you sealing at, and what has to be finished before you get there?
• What does the seal certificate show, and when do I get a copy?

When Is Aerosolized Sealing Not the Right Call for Your Project?

We use this in all our projects so you'd expect us to argue for it. Here's the other side. Permits that you get ahead of a change in the code are still going through the system, and we have jobs being completed with older permits ourselves. If your ADU permit is one of those, your rater is holding you to a looser target, and paying for a sealing pass when careful detailing and a good insulation package will take care of isn't money well spent. Ask your rater to show you both ways before you decide.

There's also another scenario where the builder owns the equipment. A builder who owns a blower door and tests his own buildings as construction moves forward can find leaks and close them with caulk, foam, and tape, and then ask for an aerosolized pass if the number won't come down on its own. What separates it from doing nothing is that it gives you a measurement at every stage. A builder who tells you the building will be fine and hasn't got a test to prove it, only has hope, not a method.

And a gap you can see isn't a fogging problem. The fogging will close gaps up to about half an inch. If there's a hole you can see in the outside of the ADU, somebody needs to close it by hand before anyone pressurizes the building, and any honest installer will tell you the same thing.

Getting the Air Tightness Number Settled Before You Sign

The decision you need to make isn't whether aerosolized sealing is good technology. It's whether the estimate you're going to sign has a stated testable plan for achieving the air tightness that the rater requires for your ADU. If that plan is going to cost $1.00 to $1.50 per square foot, you know what you are buying, when it happens, and what proof you'll be given. If there's no plan at all, that is a discussion you need to have before the contract is signed, not after.