Corgan, a Dallas-based architect with 16 U.S. and three overseas offices, is shedding light on the least scrutinized area of carbon dioxide equivalent (CO2e) emissions accounting in structural material extraction and processing. A team from the firm’s Echo sustainability practice and Hugo research group released a white paper, “Understanding Real CO2e Emissions in Mass Timber Production,” in conjunction with last month’s launch of the Corgan Mass Timber Carbon Calculator.
The paper presents life cycle assessment (LCA) considerations underlying carbon accounting for mass timber building elements or assemblies, including those of cross laminated timber (CLT) or glue laminated timber (GLT) design. The LCA universe broadens as authors examine seven tree species yielding construction-grade mass timber: Alaska Yellow or Western Red Cedar; Douglas, Hemlock or Spruce Pine Fir; and, Ponderosa or Southern Yellow Pine.
“Understanding Real CO2e Emissions” focuses on carbon released in the management of slash—roots, bark, branches, foliage and other cedar, fir or pine logging operation debris or waste. Slash is rich in carbon but, in sharp contrast to hardened concrete, weak in CO2 storage potential. “Up to 50 percent of a tree’s dry weight is sequestered as carbon through its lifecycle, however, with current timber harvesting practices, trees lose a significant amount of their stored carbon via slash,” paper authors observe. Mindful of those practices, they look at carbon loads of slash management scenarios:
- Pile burning, where waste and debris are torched in a controlled environment, releasing nearly all carbon.
- Site composting, where slash and log leftovers remain in the environment, releasing upward of 90 percent of carbon over a 10-year period.
- Mastication, where waste and debris are processed to mulch—routinely involving costly, specialized equipment, and spread across the forest.
By outlining LCA essentials from live tree to sawmill to CLT or GLT production, the Corgan Echo and Hugo team reveals CO2e volumes that wood construction proponents have traditionally been able to gloss over when pitching their alternative to concrete or steel load-bearing elements. Team members frame slash management metrics’ importance in the face of a 2023 World Resources Institute report, The Global Land Squeeze: Managing Growing Competition for Land, and a concurrent article, “Wood Is Not the Climate-friendly Building Material Some Claim it to Be.”
Article authors serve up critical takeaways for carbon-minded construction interests to ponder, none more than these contentions: “Harvesting wood is not carbon-neutral” and “Using wood in construction will most likely increase climate warming for decades.” Widespread mass timber adoption, the authors observe, will compound global wood harvest activities, annual CO2 emissions from which are on track to reach 3.5 billion to 4.2 billion tons toward 2050. At that volume, wood construction interests would find their structural material of choice associated with the source of 8-10 percent of global CO2 emissions—a level much in line with finished concrete construction as well as steel production overall.
WRI discussion culminating in the Corgan white paper and Mass Timber Carbon Calculator started just ahead of the Global Land Squeeze release in a report, “Greenhouse Gas Emissions from Global Wood Harvests are Vastly Undercounted.” Princeton University Senior Research Scholar and WRI Technical Director for Ecosystems Tim Searchinger attributes his and co-authors’ premise to “faulty carbon accounting.”
The Corgan team addresses flawed number crunching with a credible, transparent view of the CO2 emissions attending production and transportation factors surrounding wood harvesting and CLT or GLT.