The purpose of this building study is to use whole building life cycle assessment (WBLCA) and cost estimates to understand the embodied carbon and dollar cost differences between functionally equivalent mass timber and steel structural systems. The study compares a reference mass timber building—the Burwell Center for Career Achievement (Burwell Center), located in Denver, Colorado—with an alternate steel design. Comparisons between the two systems are made in terms of embodied carbon, construction dollar cost, and construction speed. The architectural variations (construction type, enclosures, fire protection, acoustic performance, and ceiling finishes) between these designs are included in the analyses. 

The Burwell Center building study is intended to be read together with the Mass Timber Comparative Life Cycle Assessment Series Introduction, which details aspects common to all studies in the series, including methodology, approach, scope, and code compliance of the comparative designs, LCA, and dollar cost analyses, and the importance of embodied carbon and biogenic carbon as part of the building industry’s strategy to address climate change and environmental degradation. This study details the information specific to Burwell Center and variations from the series introduction. 

Project Background and Alternative Designs 

Completed in July 2020, Burwell Center is a Type III-B, three-story building that houses the university’s career services program with classrooms, open office areas, conference rooms, interview rooms, and ancillary spaces for graduating students, alumni, and university organizations. The Architect of Record is Lake|Flato, the Consulting Architect is Shears Adkins Rockmore, the Structural Engineer of Record is KL&A Engineers and Builders, and the general contractor is PCL Construction Services, Inc. The authors of this study utilized information from the completed construction documents as the basis for analysis. 

Mass timber was chosen for its architectural value, specifically the warmth and biophilic benefits it would bring to the indoor environment and ability to visually express the structure, as well as its relatively low embodied carbon impact and ability to support LEED certification goals. Designed to minimize both embodied and operational carbon impact, the project is LEED v4 Platinum-certified and “net-zero-ready”—i.e., an all-electric building capable of achieving net-zero carbon once broader campus improvements are complete. 

A steel system was chosen for the alternate design based on local construction practices. It is commonly used for buildings of this scale in this part of the country. 

Comparative Building Systems

Figure 3: Schematic 3D images of the two alternate buildings – mass timber (left) and steel (right)

Reference Building – Burwell Center

Burwell Center has a total gross floor area of 22,990 ft² (2,136 m²) and includes three stories above grade and no below-grade construction. A schematic building section is shown in Figure 4. The foundation system is concrete grade beams spanning between concrete drilled piers varying in diameter from 18 to 24 in. The core walls are supported by concrete tie beams on void forms spanning between drilled piers. Level 1, which is a 5-in.-thick concrete slab-on-grade, includes a lobby, open office and co-working spaces, conference rooms, and storage space. Levels 2 and 3 and the roof utilize a mass timber structural system, and include office space, lounges, and conference rooms. Above the roof is a custom steel structure supporting a photovoltaic (PV) panel array.

Figure 4: Schematic building section of Burwell Center

The Type III-B mass timber system can be described as post-and-beam framing. The floor assembly is comprised of 3-ply (4-1/8-in.-thick) cross-laminated timber (CLT) panels with 3/4-in. acoustic underlayment mat and 3-in. cast-in-place concrete topping slab with finishes above (Figure 5), supported by glued-laminated timber (glulam) beams and columns.

Figure 5: Mass timber system floor assembly

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For more information, see the Mass Timber Comparative Life Cycle Assessment Series Introduction and comparative LCA building studies on the following projects: 

• Return to Form 
• Nez Perce-Clearwater National Forest Supervisor’s Office 
• 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.