Whole Building LCA - Eutrophication & Acidification impacts of CLT and Glulam

Asking for insight on eutrophication and acidification impacts of CLT and Glulam when documenting WBLCA for LEED. I am working on a project that is using CLT and Glulam. When comparing proposed wood based building with baseline concrete and steel, I am seeing a significant decrease in global warming potential but a large increase in eutrophication and acidification. I believe this is mostly due to fertilizers, and may vary based on how sustainably wood is harvested. Anyone encountered this?

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Hi Bipin, yes, this is an issue a few of us have run into with this credit. @iancho pulled together data and comments from a few firms and submitted a question to the GBCI. The response from the MR Tag group suggested we use a different LCA software (One Click LCA) and see how the results are. We’re pushing back on this and still waiting for a response. I’d be interested in seeing what success others have had with this credit and mass timber. Your thoughts are probably correct - there’s a difference in A-stage numbers that can’t be compared between the two vastly different material production methods.

In the mean time, I’ve also heard that firms are having to track design changes after the switch to mass timber to try and hit this credit. Not an ideal path, as it means that a large portion of the GWP reductions are ignored at this point.

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Hi Bipin - do you have a LEED project number? I could include it in a follow-up email to the MR TAG. We have 4 projects I know of so far who tried to document the life cycle impact reduction credit when switching from concrete to mass timber systems, and all are reporting the same issue with increases in non-GWP impact categories.


I have also experienced the same, with Tally for Revit, as well as with One Click LCA databases for a few European countries.

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Was having a conversation about this recently, and it led us to talking about absolute impact. Eutrophication and acidification are even harder to conceptualize than carbon. Think we can agree that ideally we don’t want to have any negative impact, but when there is some relative percent increase, how confident are we that it is of an appreciable magnitude to outweigh the impact from other categories?

There is some precedence in LEED around significant figures and rounding down to zero when the numbers are really small.

I’d be interested to hear what others think!

LEED v4.1 BD+C guide excerpt


I am working on OneClick LCA software and it shows similar results. We are planning to use sustainably harvested timbers and glulam, but have not finalized vendors. I will reach back with how it impacts overall eutrophication and acidification impacts.

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Alex - We are very early in design phase, so the project is not registered in LEED Online. I will share you LEED project number once we register the project. I saw in LEEDUser forum that consultant are documenting some CLT or Glulam in baseline or including products with high eutrophication & acidification in baseline to hit reductions all 6 impact impact categories.
Link: https://leeduser.buildinggreen.com/forum/wblca-eutrophication-impacts-wood

@Luke-Lombardi this was one thing that we tried to find when we first ran into this issue. There are weighting schemes out there, one set is in the CLF LCA guide (Page 28). But even the weighting schemes have issues we couldn’t quantify. Per our (limited) understanding, Eutrophication and Acidification are more locally impactful, so it’s hard to compare them to something like the global impact of carbon. That said, this credit might be improved by first applying a scheme that would result in an easier process to switch structural material.


@iancho please could you include us in the follow-up email? We have the same issue. The LEED project number is 1000133364, my email xramon@greenlivingprojects.com

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@bkarki1 I had the same issue on a LCA we were performing, the conversation PoCP impact in CLT Structure Buildings - #3 by xramon I started is in the same page of what you posted.

My conslusions so far were:

Conclusion 1: POCP seems to be higher in a CLT structure if compared with a Reinforced Concrete structure.

Conclusion 2: POCP in CLT is produced in A1-A3, specifically in A1: extraction and process.

Conclusion 3 (to be confirmed): Terpene seems to be the responsible of higher POCP in CLT during A1 phase ¿?

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We’ve had the same issue using Tally for a MT building. We plan to take the approach of setting the baseline to also be MT and only count the benefit from low-carbon concrete.

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Hi @iancho ! Do you have any update about the follow-up email to the MR TAG? I’d love to know more about other projects that are reporting the same issue with increases in non-GWP impact categories when switching from concrete to mass timber systems.

My findings so far here: PoCP impact in CLT Structure Buildings - #3 by xramon

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Hello all!
Did we ever receive any guidance from USGBC/GBCI on this?

Hey everyone,

We’ve run into the same issue, so glad to see this thread pop up. I view it slightly differently however, and it may not be a popular opinion …

I think part of what is underlying all of this is that so much of the industry wants wood to come in and save the environmental day and it doesn’t. No matter how well-sourced wood is, there are still impacts. And I think that LEED actually has this one right to require us to ensure that we don’t increase other impacts while driving down others.

Don’t get me wrong … I love a good LEED bashing session, and if they come back and say that we can discount acidification and eutrophication (perhaps assuming other criteria are met for wood sourcing), that would be a great benefit to many of our projects. But we need to be honest with ourselves that while good wood (and making sure it’s good wood is another rabbit hole) does help from a carbon standpoint, it’s not a magic wand.



Think there’s been a healthy growing discussion around the nuances with wood; neither blindly saying it’s good or bad. It’s challenging because numbers are how we justify decisions, but there is certainly a lag between actions needed a day before we have all the information in hand. I appreciate the perspective of this article (shout out @Aurimas !) that underscores the importance of knowing where your wood comes from and building relationships with foresters–similar to relationships we’re building with ready-mix suppliers for concrete.