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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.