I love wood, but are we subtracting biogenic GWP from fossil GWP when presenting climate impacts? Practice seems to be maturing fast, helped by EN 15804 +A2. But I’ve become a bit cynical of long-term biogenic landfill storage values making their way into the top line of our results. Am I wrong on this? Thanks in advance for your thoughts
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Hi Stuart -
Great question! it’s definitely a loaded, incredibly nuanced topic…
Agreed that EN15804+A2, alongside some of the other publications coming out are really seeming to advance the biogenic carbon accounting conversation in North America (see the Naturallywood paper & the Canadian wbLCA Practitioners Guidelines linked below)
The key thing for me is that at this point in time, it appears inappropriate to report only 1 GWP result if you’re working on a project using biogenic materials. Ideally, we provide one result with “FossilGWP” only and one with “FossilGWP-minus-BiogenicSequestrationGWP”. An example of this is the Vienna House study I was involved in - it’s also linked below.
However, before taking credit for biogenic I believe we need to have confidence that our wood comes from responsible sources; so either salvaged/reused material or from forest stands using forestry practices that not only avoid decreases in national forestry stocks (the ISO definition of “sustainable”, which in my opinion is weak), but that actively contribute to the restoration of forest ecosystems. I don’t have confidence that many wood product labels meet that standard yet - and good luck getting that information for typical dimensional lumber today. It gets even trickier when we do not design for disassembly and therefore there’s a risk that the wood products may biodegrade upon the End-of-Life of a building. When we look at the EPD from Kalesnikoff for their CLT (also linked below), assuming the product isnt reused, C3/C4 basically emits enough to cancel out all biogenic carbon stored in Stage A.
https://nrc-publications.canada.ca/eng/view/ft/?id=533906ca-65eb-4118-865d-855030d91ef2
Thank you for these resources Jeremy - ViennaHouse is a great project! I had not seen the biogenic primer from naturally wood.
We’ve been feeling more pressure to provide audit-grade accounting, and it’s very clear that biogenic must be zero when wood products exit the system for reuse, combustion or down-cycling. However, when we assume landfilling (i.e. North America) biogenic carbon provides a significant benefit - if you subtract the GWP_biogenic from the GWP_fossil when reporting. Aside from this being a perverse incentive, my concern is that even though condoned by LCA methodology, I don’t think we’re supposed to be combining different GWP impacts - right? I feel like I’ve seen this in ESRS / CSRD and GHG Protocol and maybe even IFRS S2? I think the last draft of ASHRAE 240P also excluded biogenic carbon from results.
There is a heap of guidance from the wood industry on how to count biogenic carbon. Not so much from the LCA world - at least that I have found, please let me know if you have! These are a couple articles that have influenced me - tugs at the biodiversity heartstrings… thinking of clearcutting those stands filled with bugs and birds and fungi every 50 years…
https://www.istructe.org/journal/volumes/volume-99-(2021)/issue-1/timber-and-carbon-sequestration/
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