The tests, carried out at SwRI’s laboratory in San Antonio in spring 2025, were designed to evaluate whether hybrid mass timber systems can hold up under extreme fire conditions while bearing structural loads. The results confirmed that these assemblies—featuring cross-laminated timber (CLT) floors from Stora Enso and glulam beams and columns by WIEHAG—can perform on par with conventional steel and concrete systems.
This testing milestone specifically addressed a long-standing gap in the market: the absence of validated fire resistance data for common timber connection types under high-stakes scenarios.
According to Josh Dortzbach of Forefront Structural Engineers, "One major challenge for the success of, not just the Edison, but future tall timber buildings across the industry, was that many standard connection configurations had never been tested under a 3-hour fire-resistance rating (FRR)—a requirement essential to advancing tall mass timber construction, following the fire rating standards for IBC construction types I-A."
The successful completion of the final column tests in August 2025 caps a full-scale validation effort, supporting Neutral's own Milwaukee high-rise, which is set to become the tallest hybrid mass timber structure in the country.
Neutral’s approach extended beyond engineering: they’re releasing the full test data publicly, an unusual move in a field where proprietary testing is the norm. This decision aims to remove technical and financial barriers for other developers interested in sustainable high-rise timber construction.
“As we look to build more sustainably, there is value in making fire resistance tests available so that they can be utilized by other developers and designers as part of their justification for a high-rise mass timber building,” explained David Barber of Arup, the project’s fire protection consultant.
The fire testing initiative was the result of a multi-firm collaboration, reflecting the broad coordination required to move mass timber forward. Forefront Structural Engineers led the structural validation; Arup managed fire engineering; CDSmith served as general contractor, and HPA led the design.
According to Daniel Glaess, Partner and Chief Product Officer at Neutral, “True sustainability demands deep collaboration among developers, engineers, manufacturers, contractors, and future building users. Together, we’re not just building better buildings—we’re engineering a more sustainable future.”
Beyond a single project, the real impact lies in how these results might shift the broader market. With the International Building Code now providing pathways for tall timber structures, verified performance data could help more developers, engineers, and city officials gain confidence in mass timber as a viable material for high-rise construction.
