Designed by Walter Netsch of Skidmore Owings and Merrill to be a multi-denominational place of worship, the United States Air Force Academy Cadet Chapel is considered among the premier examples of modernist architecture with its minimalist style and use of modern materials. Completed in 1963, the iconic structure in the heart of the Cadet Area of the Academy touches the lives of all that come to visit and study. The Chapel was awarded the American Institute of Architects’ National Twenty-five Year Award in the 1990s, it is a National Historic Landmark, as a part of the Academy’s Cadet Area, and it holds the distinction of the most visited man-made structure in Colorado.
Historic preservation of the Air Force Academy Cadet Chapel
Photo courtesy of WJE
Netsch’s creation of steel, aluminum and glass, seems inspired by the cathedrals of Europe, the mountain peaks of the surrounding terrain, and the industrial skin of the Air Force’s modern aircraft. It is a brilliant piece of work, marred only by its inability to protect people and religious artifacts inside from water as the building has suffered from rainwater leaks since construction.
Over the years, the Chapel has endured several repair campaigns, starting just as the original construction was ending, including over-cladding many of Netsch’s original details. Multiple generations of storm windows have masked the character-defining “dalles de verre,” colored art glass-block windows that provide the unique colors within the Protestant level main chapel space. Unfortunately, each of these previous repair efforts ultimately proved unsuccessful.
Early in the 2010s, the Air Force initiated the monumental task of addressing the underlying and persistent issues with the building’s enclosure that were the source of this water leakage. Addressing the leakage while maintaining the aesthetic and historical character of the Chapel would not be an easy undertaking. In 2014, The Air Force Civil Engineering Center turned to AECOM and their assembled team of subconsultants in the Colorado Springs, Colo., and Indianapolis office, to face this challenge. As the exterior wall consultant, Wiss, Janney, Elstner Associates Inc. (WJE) was tasked with designing a weathertight solution while working alongside AECOM’s Historic Preservation consultant, Washington, D.C.-based Hartman-Cox Architects, to also restore the building’s original iconic appearance.
Solving the water infiltration problem began with understanding the original design and construction along with the problems that plagued it. For the latter, WJE had already documented and investigated the building’s water infiltration during a prior project. To augment that work, WJE engaged in an archive search that revealed not only the original structural steel and aluminum cladding shop drawings, but numerous construction period photographs as well.
Photo courtesy of the United States Air Force Academy, Special Collections
The Chapel structure is primarily comprised of shop-fabricated trusses of 6-inch and 4-inch diameter structure steel tubes in a unique “tetrahedron” arrangement—in essence a four-sided pyramidal space frame structural unit. The tetrahedron are then erected to “lean” inward creating the A-frame volume that defines the Protestant level Chapel. This tetrahedron pattern was repeated to create the 17 spires and the 16 intervening spaces, with adjacent tetrahedron groups separated by the strips of colored glass block extending 150 feet from the Protestant level floor to apex of the vaulted ceiling and back down the other side.
This steel superstructure was then covered with a clear anodized aluminum skin of ganged, striated planks and profiled trim extrusions. Shop-assembled cladding panels were delivered to the site, hoisted onto the side of the superstructure, and anchored from inside void spaces within the tetrahedrons. The cladding provided a single-line barrier to rain intrusion with no effective means of managing any water once it bypassed the cladding plane.
The WJE proposed solution is to transform the aluminum skin of the building into a modern-day rainscreen design. With such an approach, the enclosure system requires two separate layers—an inner layer, designed as an airtight and watertight barrier, and an outer skin that replicates the original anodized aluminum cladding. Water that may penetrate the outer skin is stopped by the inner skin. However, both skins must be designed so that the outer skin maintained all original cladding profiles and planes. Since the original cladding fits close to the steel superstructure, there isn’t room to place the inner weather-resistive skin out beyond all the steel framing. However, the void spaces of tetrahedron volumes allow a bit more flexibility. Further, the repetitive, almost industrial, nature of the basic structure provides the opportunity to develop a prefabricated panelized approach to the weather-resistive skin behind the new cladding.
Photo courtesy of the United States Air Force Academy, Special Collections
In order to create the rainscreen system, complete removal of the original cladding is necessary; returning the Chapel to the original steel skeleton frame to start anew. However, this time the installation must proceed from the inside out. The exterior cladding can no longer be anchored from inside of the tetrahedron volume with the weather-resistive skin in place.
With this basic enclosure concept in place, further development of the Chapel’s rainscreen design was driven by the following goals:
- Develop a cladding that mimics the original design to the fullest extent possible.
- Limit joints within the weather-resistive barrier.
- Develop a durable weather-resistive barrier to reduce potential need for future access.
- Avoid penetration of the weather-resistive barrier for cladding installation.
- Develop a weather-resistive barrier robust enough to withstand full exposure to the elements.
- Preserve reasonable access to joints within the weather-resistive barrier, where possible, for future maintenance.
- Accommodate structural and environmental movement within the weather-resistive barrier and cladding.
- Permit design to maximize shop fabrication due to the unique access challenges on the building.
- Reveal concealed elements of the original design hidden by previous unsympathetic repairs.
The resulting design has an inner aluminum skin made up of shop-fabricated aluminum structural panels fitted between and anchored to the tube steel frames of the tetrahedron structure. Accessories welded to the face of the panels serve as anchor points for the outer cladding. This allows for quality assurance testing of the weather-resistive skin with the knowledge that field attachment of the cladding will not result in holes through that barrier. To bridge the gap between weather-resistive panels, aluminum sheet metal covers are installed over the structural steel tubes, with silicone sealant providing the continuity between the panels and covers.
Photo courtesy of WJE
While the original cladding panels include striated planks ganged together and bounded by profiled trim pieces and anchored from the interior, such an approach was not possible with the inner weather-resistive barrier installed. It was necessary to alter the erection sequence. Ganged planked assemblies are affixed to the weather-barrier with a series of anchors designed to accommodate the anticipated cladding movements. After the planked panels are secured, profiled trim components, matching the original trim are secured in place to complete the cladding. These trim components conceal the sealant joints of the weather-barrier. No weather seals are provided at the cladding layer.
The new cladding will reveal details that have been buried under layers of sheet metal. At the art glass windows, a new integrated outer glazing system of low-iron laminated glass will once again allow the dalles de verres to be seen in their intended brilliance. The result will be a building with a high-performance contemporary rainscreen cladding that maintains the aesthetics of the 57-year-old modern architecture marvel. Netsch’s true vision will finally be expressed, and this icon will be preserved for generations to come.
Bryan Rouse is an associate principal at Wiss, Janney, Elstner Associates Inc. in Chicago. He is a registered architect, having obtained his Master of Architecture degree from the University of Illinois, Urbana-Champaign. Rouse has 24 years of experience investigating and repairing existing structures, specializing in components of the building envelope. That experience spans hundreds of projects across the United States ranging from failure investigations to historic preservation. He can be reached at (312) 372-0555 or brouse@wje.com.