The Glass House continues our ongoing commitment to architecture and preservation with the replacement of two cracked glass panels in the Glass House.

Originally completed in 1949, the Glass House features floor-to-ceiling plate glass exterior walls held in place by steel stops and black-painted steel piers of stock H-beams that expressed the mass-produced, industrial materials employed for its design. In the summer of 2019, two of the home’s 17’-8” x 7’-10” panes of existing glazing cracked due to thermal stress. The stress was caused by temperature differentials and a lack of movement within the original steel frame.

“The project team achieved a practical preservation solution that will serve as a guide for future glass replacements. The team turned a somewhat catastrophic material failure into an opportunity to make the building safer and more beautiful,” said Ashley R. Wilson, FAIA, the Graham Gund Architect at the National Trust for Historic Preservation and the lead architect for the glazing replacement project.

“I am extremely proud of the Glass House team, our consultants and suppliers for the exquisite outcome achieved under adverse weather conditions and project complexity due to site constraints.” said Gregory Sages, Glass House Executive Director.

While the replacement of original building fabric is often a contentious topic in the field of historic preservation, in this case the replaced glass was likely an early-generation replacement because it was 3/8” annealed glass, meaning that it was heat-strengthened glass—a technology not available yet in the late 1940s.

Although the team was not replacing the original glass, the project was not without complexity. The new glazing, provided by Canadian glass manufacturer Agnora, needed to meet ANSI safety standards, accommodate wind load (particularly challenging because of the glass’s large dimensions), avoid overloading of the existing steel supporting rail, and, of course, visually match the original design intent as closely as possible.

To accomplish these goals, the selected glass was slightly thicker, at 9/16” rather than 3/8”, and laminated with an inner layer of PVB for safety, said Wilson. To avoid potential corrosion of the steel and clouding of the glass in case the inner PVB layer gets exposed to moisture, the team added weeps to the glass pocket.

The removal of the existing glazing and install of the new presented a new set of challenges: The old glass was prone to more cracking, requiring extra care in its removal. In order to extract the glass, the steel stops also needed to be removed. The steel frames were cleaned, prepped, and painted before the system was reinstalled. Because construction took place in November 2019 to minimize conflicts with tours and programming, the workspace also needed to be heated and protected from the elements. The west wall glass required a crane to lift the glass unit over the building, Wilson contends that the thermal stress that caused the glass to crack was due to an inherent weakness and limitations of 3/8” thick glass at such a large size. But despite the unique nature of the Glass House—and its over-sized glazing units—there are clear lessons to be learned from the project about considerations when replacing glass at mid-century buildings.

While the replacement project focused more on safety and appearance rather than sustainability goals, it did take advantage of how technology has evolved since the 1940s and 1950s with the use of glazing tape and silicone sealants within the glazing pocket to provide more protection. More broadly, new glazing products such as IGUs and more effective, longer-lasting sealants can significantly improve energy efficiency for mid-century buildings, allowing for better buildings that are more highly adapted for what the 21st century will bring—global warming or otherwise.
The scope of the project included the replacement of two upper lites of 3/8” thick glass units, design of new glazing pocket details and preparation and paint of the steel window frame and stops. The entire exterior of the building was also repainted to maintain a uniform finish. The glass replacement project began in December 2019 and took approximately three months to complete. The project team included Wiss, Janney, Elstner Associates, Inc. Joshua Freedland, Principal and Sarah Sinusas,PE, Senior Associate, Stafford Steel, Franklin Glass (installer), Agnora Glass (supplier), Glass House staff and Ashley Wilson FAIA, ASID, Graham Gund Architect of the National Trust for Historic Preservation.