Streamlining Whole Building Life Cycle Assessment of Mass Timber Buildings

How WoodWorks’ new resource can guide design teams interested in undertaking a WBLCA of mass timber buildings

The design community has embraced the use of whole building life cycle assessment (WBLCA) to quantify and compare the environmental impacts of buildings. However, detailed standards for a unified approach to WBLCAs are still in development, leaving designers needing clearer direction during the assessment process. To solve this, we developed a resource to help untangle the WBLCA process. 

Part of WoodWorks’ carbon initiative, Considerations and Worksheet for Structural WBLCA of Mass Timber Buildings, seeks to outline the requirements for life cycle assessment (LCA) found in international standards and give guidance on how to perform WBLCAs for mass timber buildings using commercially available LCA tools. Our ongoing work with KL&A Engineers & Builders, who authored the Platte Fifteen WBLCA with us in 2021, also helped to shape this document.

What is the purpose of this document in relation to mass timber building design? 

Ashley Cagle: The world of LCAs is a bit like the Wild West right now. There is tremendous interest in learning about the environmental impact of our buildings—and naturally, we want to quantify that impact so we can work to reduce it. Because this is a relatively new field, and because of the urgency of our climate crisis, many people are working to rapidly develop standards, rules, guidance, and best practices. These efforts are fantastic but can lead to confusion and conflicting information. At the same time, many of the current standards don’t provide the level of specificity many designers seek, especially when looking at comparative WBLCAs of wood buildings. We’re not trying to create another LCA standard or guide document, but instead we’re walking designers through the ISO-compliant LCA process step-by-step and identifying key decision points in the context of wood structures.

How does the worksheet assist teams in conducting a WBLCA for mass timber buildings? 

AC: In theory, doing a WBLCA sounds very straightforward: Do a material takeoff, plug those numbers into your LCA tool, run the analysis, and boom—you’re done! But in practice, quite a few questions arise early in the process, things like, Do I include finishes? What about foundations? How do I develop an equivalent alternative design? It can also be confusing to understand what is “baked in” to the LCA tools versus decisions the designer needs to make. The goal of the worksheet is to outline these decision points so designers can be better informed during the planning stages of an LCA—and to provide guidance throughout the LCA process on how to answer these questions for mass timber buildings. 

Sample of the worksheet available to design teams

What common question or issue does this answer for designers?

AC: One of the more challenging aspects of performing a structural WBLCA can be defining the scope. Again, something that sounds like it would be relatively straightforward. But in my experience, LCA project teams spend a significant amount of time discussing which materials, assemblies, and systems will be included, and it can be difficult to anticipate all of the questions at the beginning of the LCA process. Are we only studying structural framing, or are we also looking at exterior enclosures and non-structural walls? Are we including any architectural finishes?  

Accurately defining the material scope becomes even more important when doing a comparative LCA between a mass timber building and conventional construction like steel or concrete. There are major inherent differences between these structural systems that extend beyond the framing members themselves. We need to ensure that all design alternatives have equivalent fire performance, for example. For a mass timber building, that might mean we need to include an additional volume of wood to meet char ratings, whereas for a steel building, we might need to include spray fireproofing material. This worksheet helps outline many of those differences so designers can do an apples-to-apples comparison of alternative designs.

Are there any tools you recommend using with this worksheet for a more comprehensive WBLCA? 

AC: I am often asked which LCA tool is best and which tool(s) to use.  We do recommend that designers use a whole-life LCA tool; that is, one that covers all life cycle stages rather than EPD-based tools that only cover cradle-to-gate (A1-A3) or cradle-to-construction gate (A1-A5) stages. Commercially available LCA tools commonly used in the U.S. include Athena, tallyLCA, and One Click LCA. Often, design teams will choose their tool based on how easily it fits into their established workflow, which is arguably the most important factor. Teams need to pick the tool that they are most likely to use because the first step is just to get started. However, there are many other differences—from the data being used to assumptions that are programmed into the tool. I always say that one tool is not better than another, but it’s important for the user to know how the one they’re using works and fully understand its results. 

What else to know 

AC: The idea behind the fillable PDF was to create a practical, useful resource that helps project teams complete comparative LCAs. It can be used to help guide project team meetings, document important scope decisions that were made, and facilitate writing a comprehensive LCA report. Most importantly, it is meant to ensure that all the unique attributes of mass timber construction are accurately captured so an accurate comparison to more conventional building materials can be made. 

If your project uses the worksheet to help guide a comparative WBLCA for a mass timber project, we’d love to hear about it.

Send Ashley a note at: ashley.cagle@chinakfbdf.com.

Have questions? Ask us anything.

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