The goal of the Mass Timber Comparative Life Cycle Assessment Series is to illustrate the embodied carbon and economic implications of selecting mass timber structural systems compared to functionally equivalent steel and concrete systems. Results to date illustrate that the embodied carbon benefits and biogenic carbon storage potential of a mass timber structural system can be achieved with little dollar cost premium relative to traditional systems.

The series is a compilation of comparative building studies based on designed reference buildings located in the United States. Some of the projects were fully constructed prior to the studies; others were in design. The reference buildings utilize mass timber structural systems and are compared to alternative systems in terms of embodied carbon (using whole building life cycle assessment, or WBLCA), dollar cost, and speed of construction. The authors have sought diversity in terms of geographic location, building use, size, construction type, and mass timber framing scheme to ensure that a variety of project types are represented.

Studies include the embodied carbon impacts of materials and assemblies associated with structural systems, vertical and roof enclosures, fire protection, acoustic performance, and ceiling finishes to create a holistic comparison of construction types and structural systems.

The introduction defines the general methodology, approach, and code compliance of the comparative design, life cycle assessment (LCA), and dollar cost analyses common to each study. The authors have endeavored to be transparent in methodology, scope, and assumptions, and specific information and variations from the general methodology are discussed within each study.

The introduction also features discussions on LCA methodology, the importance of including biogenic carbon, and decisions, considerations, data selections, and inclusions/exclusions in the context of using a commercially available LCA tool, in this case TallyLCA.

The series includes comparative LCA building studies on the following projects:

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• Nez Perce-Clearwater National Forest Supervisor’s Office
• Burwell Center for Career Achievement
• Denver Office

Authors:

This series is being developed collaboratively by KL&A Engineers & Builders / KL&A Team Carbon and WoodWorks with funding from the USDA U.S. Forest Service and the Softwood Lumber Board.