A new method of construction is gaining traction, and it has the potential to take a natural material to new heights. Mass-timber framing is characterized by the use of large, solid-wood panels for floor, wall and roof construction.

Building and non-building structures made of mass timber are typically formed from solid-wood panel or framing systems that are 6 feet or more in width or depth. The method has been underway for several years in the U.S. and it is covered in the 2018 International Building Code (IBC).

Thanks to an emerging mass-timber product category and proof of concept for larger and taller wood structures established in Europe over the past few decades, a small — but growing — number of mass timber and hybrid buildings are rising in the U.S.

Image courtesy of Fast + Epp

Code officials therefore should be aware of the potential for structural mass timber in projects. And they should be prepared to evaluate mass-timber products and assemblies to ensure they are code-compliant.

Mass timber is most commonly used in mid-rise, educational, industrial and commercial facilities. The system’s structural properties allow project teams to maximize their site’s footprint while differentiating the building with wood’s aesthetic, environmental and thermal efficiency features.

Understanding wood’s role

Mass-timber products include cross-laminated timber (CLT), nail-laminated timber (NLT), dowel-laminated timber (DLT) and glue-laminated timber (glulam).

Mass timber panels and beams shape this four-story, 16,000-square-foot commercial office building in Portland, Oregon. Project: Albina Yard | Architect: LEVER Architecture | Photo: StructureCraft

Code officials should be aware of the following characteristics of mass timber — including seismic, fire and wind resistance — to ensure it is safely, efficiently and effectively used in construction.

Code Compliance. Wood product manufacturers hold ICC-ES evaluation reports for their mass timber products demonstrating compliance with the IBC and IRC requirements.

Fire and Life Safety. Wood naturally forms an outer char layer when exposed to extreme heat or fire, allowing the structure to continue to support the building while it is evacuated. That allows its use in larger buildings and expands options for exposed wood structure in smaller projects.

Component Assembly. Prefabricated CLT, NLT, DLT and glulam components assemble as a unified system with cutouts pre-planned.

Thermal Conductivity. Wood is composed of millions of open cells that limit thermal transfer, making the material more resistant than steel and concrete.

Moisture Buffering. When properly treated for its climate and with adequate ventilation designed into the structure, wood buffers moisture while maintaining structural integrity.

Seismic Resilience. Wood construction features several, often redundant, nailed connections. That gives the assemblies a significant degree of motion, allowing them to respond to seismic activity without failing critically.

Acoustic Properties. Designing a space for people to enjoy means accommodating their experience. Wood structures and finishes can be designed in a way that amplifies and enhances sound — or quiets it.

These glulam beams burned predictably when put to the test. Mass timber chars, protecting the inner structure.

Learn More

To deepen your knowledge of mass timber construction you can:

  • Explore our research library. We continually update our third-party research library to provide you the latest on wood performance and mass-timber building products. Our white papers, podcasts and other materials are sortable by performance criteria, building technology and more.
Disclosure statement: The views and opinions expressed in this article are those of the Think Wood and do not necessarily reflect those of the International Code Council, or Hanley Wood.