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EcoSeal: A New System for Air Sealing Homes

Knauf EcoSeal, a sprayable caulk installed prior to cavity-fill insulation, can provide a significant reduction in air leakage

Posted on Apr 18 2013 by Alex Wilson

Getting back to our Dummerston, Vermont farmhouse this week, I’m reporting on our use of a relatively new product for air-sealing homes: EcoSeal from Knauf Insulation.

First some context: In the building science world, there is growing interest in achieving a robust air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. at the sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. layer of a house, with layers inside of that able to dry toward the interior and layers on the outside able to dry to the exterior. To make that work, the sheathing layer has to be tightly air-sealed.

In our house, we used from Huber Engineered Wood as the sheathing layer, taping the joints. Zip System sheathing is an oriented strand board (OSB) sheathing that has a coating to improve weather resistance and reduce permeability — so it makes a great air barrier. The version of Zip used for wall sheathing is green and the version used for roof sheathing is a reddish color. Huber also distributes a — the tape is manufactured by 3M — that’s used for sealing joints and edges of the Zip sheathing.

It's tricky to air seal an old house

In working with an older house like ours, there are inevitably some irregularities that make air sealing with the sheathing more difficult. With our house (originally built in the early 1800s), for example, there are beams at the top of the eave walls that extend 4 inches out from the wall plane (oddly), and we had to box those in with the sheathing. There may also be some air leakage at the joints, despite the taping.

So to achieve an airtight sheathing layer, it helps to add some air sealing from the interior. Some builders use a “flash and batt” system for this: a thin layer of spray polyurethane foam (SPF) is applied against the sheathing from the interior (up to about an inch thick) and the cavity is then insulated with batt or other cavity-fill insulation. The SPF is great at air sealing but pretty expensive as an insulation material, so flash-and-batt is a reasonable solution.

Another solution is to use one of two new products for sealing just the joints and cracks at the sheathing layer. Owens Corning makes the system, and Knauf makes . (Warning: this last link opens with an installation video that has a somewhat jarring soundtrack).

An acrylic air-sealing system

EcoSeal is an acrylic product that is applied using high-pressure paint-spraying equipment. The installer arrived with two 5-gallons buckets of the bright-blue acrylic material that was the consistency of very thick paint. The system comes with a long, 200-foot hose, so the pump and bucket can stay in one place in the house while the work proceeds. The pump is very quiet.

The installer started on the first floor and worked methodically around the room sealing all the joints and cracks, and then moved upstairs. We had arranged for someone from to come down with a blower door (a device used for testing the airtightness of a house) and run the blower door during the EcoSeal installation.

Here’s how a blower door works: a fan in the blower door depressurizes the house enough to maintain a 50 pascal difference is air pressure between the inside and outside — as measured by an integral manometer (air pressure gauge). Instrumentation in the unit calculates the cubic feet per minute (cfm) of air flow going through the fan to maintain the 50 pascal pressure difference.

The blower door, as we used it, did two things: first, it exaggerated the air leakage so the installer could feel cracks that needed sealing; and second, it allowed us to measure the success of the air sealing.

EcoSeal doesn’t expand as it is installed (as do foam sealants), and it takes up to day to fully cure. The cure time depends significantly on the environmental conditions — temperature, humidity, etc. Our house was fairly cool during installation, so the cure time was significant. The material can span up to about a 3/8-inch gap, according to Knauf, and it remains flexible.

If EcoSeal gets on surfaces where it doesn’t belong (as occurred once during our installation when some got on one of our windows), it easily washes off with water. We were in the house throughout the installation and could barely smell it, so I’m confident that it has low VOCVolatile organic compound. An organic compound that evaporates readily into the atmosphere; as defined by the U.S. Environmental Protection Agency, VOCs are organic compounds that volatize and then become involved in photochemical smog production. (volatile organic compound) emissions.

Significant measured improvement

When we started EcoSeal installation, the blower door was showing 950 cfm of air leakage at 50 pascals (cfm50). During the course of about four hours of work on the air sealing, that air leakage rate dropped to 640 cfm50. That’s an improvement of a third — not bad.

Given the volume of the house, 640 cfm50 is equivalent to 1.6 air changes per hour at 50 pascals (ach50), which is very respectable for a new house, let alone a renovation.

EcoSeal costs about $1,000 to $1,500 per house

Knauf Insulation introduced EcoSeal in January 2011. It’s still a very new product, with only 100 installers nationwide, according to Brett Welch of the company. He estimates that about 2,500 homes have so far been sealed with the system.

In houses where there hasn’t been as much attention paid to air tightening (no taped sheathing), a more typical tightness achieved is between 2.5 and 3.0 ach50. Welch said EcoSeal has also been used in a few PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. projects, where airtightness of 0.6 ach50 must be achieved.

EcoSeal costs $200 to $250 per 5-gallon bucket, according to Welch, with 2 to 3 buckets typically required for a house. He estimates 6 to 10 hours of labor for an installation, bringing the total installed cost into the $1,000 to $1,500 range. It can be installed at temperatures ranging from 20°F to 115°F, though at the low temperature range, the material in the bucket must be fluid and the cure time is longer. It can be stored at 35°F to 120°F.

Similar system from Owens Corning

While Knauf’s EcoSeal is a one-part system, Owens Corning’s EnergyComplete is a two-part system that is foamed in place. It expands slightly as it is installed and sets up very quickly — in less that a half-hour. I don’t have personal experience with EnergyComplete, but visited a Passivhaus building under construction in Palo Alto, California, in late 2010 that had just been sealed with the system, and was impressed with it.

[Editor's note: For a comparison of EcoSeal and EnergyComplete, see Air Sealing With Sprayable Caulk.]

Alex is founder of . and executive editor of . In 2012 he founded the . To keep up with Alex’s latest articles and musings, you can .

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  1. Alex Wilson

Apr 18, 2013 10:35 AM ET

a few thaughts ..
by Jin Kazama

I like the idea of the product, doesn't look like it uses alot of material either, but it is only efficient if you can't remove exterior sheathing ...

i may sound redundant, but at 1500$ i'm confident it would've paid a nice complete wrap with peel stick , and would've probably help achieve a better seal ??
( and u would've save on the taping labor )

Was the blower run while spraying or shortly after ??
If so, wouldn't it blow holes through the liquid material where air leaks ??

Apr 18, 2013 2:49 PM ET

Them's pretty tight specs
by Dana Dorsett

That 950cfm/50 number is pretty tight starting point for any house, let alone an early 19th century antique! (To start out that tight requires a construction crew that all matriculated from the Air Tightness Academy.) The EcoSeal goo seems like pretty-good icing the already-decent cake though!

Depressurizing the house during installation may make it easier to find the leaks, but I'd think that pressurizing the house instead would have the added benefit of drawing the goop into the offending exfiltration path for a deeper more reliable long term seal (in much the way that dense-packing fiber insulation wedges fiber into the leakage paths, clogging them for way-better-than-damp-sprayed air tightness.)

Apr 18, 2013 8:59 PM ET

Edited Apr 18, 2013 9:02 PM ET.

Great Job Dummerston Crew
by albert rooks

The 950cfm/50 really shows how effective the crew accomplished joining the window bucks and membrane to the wall membrane. I recall pictures that incorporated careful sealing using Pro Klima tape and membrane at widow and wall.

It also goes to show how effective a membrane, or in this case, Huber Zip + tape can be on a retrofit where there is a further layer of insulation protecting it from siding fastener penetration. All those holes are avoided.

1.6 ACH50... Really good job folks!

Apr 18, 2013 10:50 PM ET

Edited Apr 18, 2013 10:59 PM ET.

Blue Goo
by Aaron Gatzke

In Edmonton, there is a product called Blue Goo and they are using it to seal window and door flanges to the sheathing. It could be the same product but very few contractors seal the seams of the sheathing.

Apr 19, 2013 8:26 AM ET

Applying EcoSeal during depressurization
by Alex Wilson

The EcoSeal product goes on pretty thick, and I don't think it could easily have been blown out by the depressurization. Having the blower door operating during installation was handy as it helped us find the leakage sites. Had we been pressurizing the houses instead of depressurizing, I think it would have been more difficult to identify the leakage areas.

We did have to turn off the blower door periodically, as it got pretty hot.

Apr 19, 2013 11:39 AM ET

I'd doubt that it would blow
by Dana Dorsett

I'd doubt that it would blow out at a mere 50pa depressurization- that's only 0.007 psi, which would probably be enough to blow bubbles in soap, but not anything as viscous as latex paint. (It's a tiny fraction of the cavity-pressurization seen in the dense-pack example, but the stuff moves more readily than fiber insulation too.) To be sure the differences would be pretty minor, and I get how locating the leaks is easier in a depressurization scenario.

Apr 20, 2013 10:31 AM ET

Dana : i never thought about
by Jin Kazama

Dana : i never thought about converting it to PSI ..50pa looks like a number... 0.007psi looks like the pressure exerced by the weight of a b-day air balllon resting on a table :

My bad for assuming and not using maths.... again ... #n00b

Apr 20, 2013 3:52 PM ET

Edited Apr 20, 2013 4:00 PM ET.

Why it's only 50 pascals...
by Dick Russell

Converting 50 pascals (multiply by 0.1450376E-3) gives "only" 0.00725 psi, but that's just over 1 pound of force per square foot, or almost 38 lb on that 72x72 picture window in your living room. Only 50 pascals? Heck, if that's just 0.00725 psi, let's really find those air leaks, and crank the blower up to pull 500 pascals, or even 10 times that! Ummm, stay away from that window.

Apr 24, 2013 2:37 PM ET

I totally get that 50pascals
by Dana Dorsett

I totally get that 50pascals will be higher than typical wind pressures, but "only" 50 pascals isn't anywhere near enough to blow & pop bubbles in air-sealing goop applied to a seam, crack which was my point. It might be sufficient to slurp it a bit further into a crack though, even not enough to blow bubbles.

And it's still nowhere near the pressures seen in dense-packing (which probably WOULD blow out some windows if you pressurized the whole house to those levels.)

Apr 25, 2013 5:40 PM ET

Spray Foam vs
by Kirby Slack

Just wondering what the final cost for the project was? $1,000 to $1,500 for this system then add the fiberglass. How does that total cost compare to a spray foam install?
Just a comment on the flash and batt system, make sure you always get a minimum of 1.5" of closed cell to make sure you get the vapor barrier and do not move the dew point to inside the wall assembly.

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