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Building Enclosure Council Air Barrier Challenge

With nearly a decade of experience in building enclosure code-compliance, the BSA’s Building Enclosure Council felt it was time to test the theory and practice of building enclosures at the area most prone to failure: the air-barrier window interface.

The council proposed a competition. The idea was simple: Construct a wall, insert a window and run it through the rigors of Architectural Testing’s facility. Nine teams of designers, manufacturers and contractors accepted the challenge.

The competition

BSA Building Enclosure Council air barrier challenge. Photographs by J.P. McDonald.

Click image above to view slideshow.

Teams were given an 8' x 8' sheathed metal-stud framed wall with a uniform rough opening and a commercial aluminum window, and could specify additional blocking or other materials. They were charged with placing windows as if they projected into masonry, and at least one brick tie needed to be placed in the opaque portion of the wall.

Designs addressed the following:



  • Membrane over the glass fiber facing the gypsum sheathing board: Teams could choose sheet-applied membrane, liquid applied or closed-cell plastic foam.
  • Brick ties: All teams chose a two-part unit that was fastened to a stud with two screws. Teams typically fastened the units on top of the chosen membrane with the exception of the team that used a polyurethane spray foam air and weather barrier.
  • Window anchoring: This could be done with either intermittent clip angles or continuous angles that acted as a flange. The flange offered a continuous surface for sealing and anchoring, but it would make installation from the inside difficult.
  • Tie-in of window to opaque wall: For those systems without the continuous flange, the air/moisture barrier was a sealant, spanning membrane or a combination of both with one part foam as an insulation tie-in.

Rough panels were framed, sheathed and ready for the testing grid at Architectural Testing’s facility in Chelmsford at 8:30 am on a May morning, the teams gathered and were assigned their panels, materials and window units.


The day’s first challenge brought an element of real-world coordination to the competition: rough openings were constructed a bit too small. Although not a recommended practice, the windows were trimmed to fit. Teams prepared the walls with their chosen air-barrier system to the din of machinery. Panels were rolled outside for spray foam by experienced applicators, undeterred by a steady breeze. The window installations took several approaches, with a little recalibration due to their re-sizing. By 5:30 pm work was finishing up and teams headed home, leaving projects to cure for a week.

Putting it to the test

The teams reconvened to see which would hold up best. The test equipment was calibrated for the first entry, where the full panel was isolated with a 4 mil tare membrane. Upon removal, it was clear why trimming aluminum windows is not a good idea: The window seals were clearly failing. All the windows were sealed so that their performance would not affect that of the opaque wall and the window to wall joint. Using the requirements of ASTM E 330, panels were conditioned with an alternating high positive and negative pressure. Following that, the air-barrier performance of the opaque wall and joint were measured in accordance with ASTM E 283 by isolating the window and joint and then opening the joint to testing. Finally, ASTM E 331 was used to measure moisture intrusion. Negative pressure was applied on the interior and the window was subjected to intense water spray.

What was learned, and what wasn’t

We learned a lot about the systems as well as the ease and difficulty of construction. Designers gained a greater appreciation of the builder’s responsibility.

Overall, most panels performed well as air barriers. However, many failed at moisture-penetration resistance. All the failures related more to the workmanship than to the materials or details. One notable exception was a one-part polyurethane sealant that did not have the desired percentage of closed cells.

What the tests did not measure was “buildability,” environmental cycling performance or material longevity. By having the panels on wheels and easily accessible from both sides, the reality of fixing a window in an opening many stories in the air was not realized. Environmental cycles were not simulated. All systems could be made serviceable, but we need to learn more about long-term performance. Designers, inspectors and contractors all have to pay attention to the details in design, coordination and execution. Future tests could address more real-world conditions.


W. R. Meadows, Inc.
Grace Construction Products
Henry Co.
Sto Corp.
Honeywell (SPF sealant)
Bondaflex Technologies (sealants)
Blok-Lok (veneer anchors) ATI as host

Christiaan Semmelink LEED AP, AIA is a California-registered architect with 35 years experience in the Northeast. His work includes the 40-unit Astra Zeneca Hope Lodge Boston with CBT Architects, a LEED Gold American Cancer Society of New England facility which provides communal housing and outreach for cancer patients and their families; a 280,000 SF LEED Gold core and shell laboratory at 650 East Kendall Square in Cambridge for BioMed Realty Trust with CO Architects; and a wide range of project types, construction methods and build technologies. He currently consults on technical issues with The Architectural Team.

Top image: The air barrier challenge in action. Photo courtesy of Architectural Testing.

Finding inspiration in the trenches

Architects have embraced experimental fabrication and construction techniques, such as using computer numerically controlled machines, to dramatically expand the creative expression and functional performance of standard materials. But the same can’t be said for landscape architects, according to Karen M’Closkey and Keith VanDerSys of PEG office of landscape+architecture in Philadelphia.

The two practitioners hope to see that soon change, with a little help from a $10,000 BSA Research in Architecture grant.

M’Closkey and VanDerSys are using the BSA funding to explore how digital-manufacturing technologies can be coupled with ubiquitous landscape materials—in particular, the polymer products used for engineered ground stabilization, separation and structuring—to artfully manage stormwater runoff on small urban sites.

“We’re not making new materials but rather using common materials in new ways,” says M’Closkey, who (like VanDerSys) teaches in the departments of architecture and landscape architecture at the University of Pennsylvania. “Geosynthetics are readily available and very pervasive in landscape applications, from increasing water infiltration to retaining soil for site stabilization. We want to see how we can change their composition so that the materials, which are normally below grade, can be not only visible but expressed on the ground’s surface. It’s time we learn how to tap into these very functional materials as design opportunities.”

Available in sheet or cellular form, geosynthetics are currently limited, design-wise, by their uniform geometry. M’Closkey and VanDerSys plan to vary the materials’ cellular shape, density and profile using digital manufacturing equipment and then test the customized materials’ effectiveness through the installation of a temporary prototype on a vacant lot in Philadelphia.

Working with the Redevelopment Authority of Philadelphia, Pennsylvania Horticultural Society, Philadelphia’s Office of Watersheds and APM (a local community development corporation), the designers will install observation well pipes at precise points to measure and document how much stormwater is collected and absorbed. These figures will be compared with conventional infiltration trenches to ascertain the installation’s performance.

When they complete their research this fall, M’Closkey and VanDerSys plan to spread the word about their methodology and results through professional organizations for architects, landscape architects, civil engineers and public agencies, as well as through trade publications and design journals.

If the project ultimately proves successful, the designers’ new techniques may find a permanent home on another lot in north Philadelphia, as part of the city’s Green Infrastructure Initiative.

“The city is looking for innovative ways to alleviate some of the burdens on the hard stormwater infrastructure by turning vacant lots and residual spaces into active, functional infrastructure,” says VanDerSys. Given this—and with funds increasingly being directed toward infrastructure rather than toward recreational or public space—he notes that it’s more important than ever for designers to explore creative ways to use infrastructural improvements as open-space amenities. 

Genevieve Rajewski is a Boston-based freelance writer who covers science, nature, animal issues, travel, food and passionate people for acclaimed publications such as Smithsonian, Washington Post Magazine, and the Boston Globe. Her website is

Top image: Karen M’Closkey and Keith VanDerSys configured geosynthetic material to manage stormwater runoff in urban areas using digital-manufacturing technologies. Photograph by Keith VanDerSys.

Designers as captains of industry

Thermoforming is a widespread manufacturing process that produces complex designs by heating, molding and trimming sheet plastics. A $10 billion industry in the United States alone, its products are ubiquitous in everyday life, ranging from disposable cups to car door and dashboard panels.

However, it was plastic lightbulb packaging that caused a metaphorical lightbulb to flash on for designers Lee Su Huang and Gregory Thomas Spaw in late 2008.

“The eureka moment happened on a visit to a local convenience store, when we saw the plastic blister packaging that lightbulbs came in,” recalls Huang, an assistant professor at the University of Florida’s School of Architecture. “It struck us that this kind of packaging is both incredibly light and incredibly strong, and we became fascinated by the type of snap joint that fastens its various pieces to each other.”

The two designers, then students at Harvard University’s Graduate School of Design, were inspired to work together on an independent project exploring thermoforming. Now—despite being separated by careers some 500 miles apart—Huang and Spaw are continuing that research with the help of a $10,000  BSA Research in Architecture grant.

“What we are interested in is reappropriating technology that isn’t commonplace in the architectural realm but that has a lot of potential,” says Spaw, a lecturer at the University of Tennessee’s School of Architecture. “We think architecture could benefit from thermoforming’s inherent advantages: the material’s lightness, low cost and readily accessible manufacturing technology.”

Thermoforming also allows for rapid turnaround time in the R&D of new products: Once a mold has been completed and tested, thermoforming can mass-produce pieces as quickly as one unit per minute.

Meanwhile, the polyethylene terephthalate (PETG) plastic most commonly used for thermoforming has the highest recycling rate of all plastic types, while recent industry developments have made it possible to produce PETG plastic from sugarcane instead of fossil fuels—transforming plastics into an environmentally viable building material of the future.

The researchers are taking a two-prong approach to their project.

For starters, they plan to work with the University of Florida’s Materials Science & Engineering Department to test the strength of the snap joint used in thermoforming.

“No one has really tested how viable that joint is for architectural applications,” explains Huang. “That’s why we’ll work with materials scientists. They have universal testing machines, which can mount a snap joint correctly and then test how much force it takes to either pull it apart or cause the joint to fail.”

The team next plans to create a full-scale building prototype that “is very lightweight and smart, but also simple,” says Huang. “We hope to design a structure that doesn’t require any tools to put together. We imagine pieces that could be shipped to a disaster area as easily as plastic food cartons and then snapped together onsite to create emergency housing.”

After they finish their research in December, Huang and Spaw hope to present their work at conferences and events on innovative fabrication. In addition to publishing their results and findings, they also hope to exhibit the full-scale constructed prototype at different venues across the country.

The designers believe that their idea is the natural progression of the trend toward digital design and manufacturing seen in architecture schools today.

“In effect, that is thermoforming—only at a cottage-industry scale,” says Spaw. “This grant will help us push this type of design to the industrial level.”

Genevieve Rajewski is a Boston-based freelance writer who covers science, nature, animal issues, travel, food and passionate people for acclaimed publications such as Smithsonian, Washington Post Magazine, and the Boston Globe. Her website is

Top image courtesy of Lee Su Huang and Gregory Thomas Spaw.

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