PoCP impact in CLT Structure Buildings

Structural
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Hi CLF Community!

I’m aware that this is a “carbon” forum, but other impacts behind GWP should be also taken into account such as AP, EP, POCP, if we really want to adress the whole environmental issue. Hopefully you will find interesting this topic, I’d love to hear some feedback!

I’ve noticed that in a reinforced concrete structure builidng, PoCP impact is not nearly as important as in a CLT structure building, see graph bellow

buildings compared
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Blue colums: Reinforced Concrete Structure
Red columns: CLT structure

Note that in previous graph, proposed building (CLT) demonstrates always a better environmental performance if compared with a baseline building (concrete) except in one impact category: Formation of ozone potential in lower atmosphere (PoCP)

When digging in for answers I could confirm that in the CLT structure building, indeed the CLT structure material was the most representative material contributing to the PoCP impact

chart
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Why PoCP is higger in CLT if compared with reinforced concrete?

In the following LCA “https://www.americanhardwood.org/sites/default/files/download/2017-11/Endless_Stair_LCA_final%20report.pdf” it’s mentioned that:

“The large percentage of PoCP during material production (wood) is due to emissions of terpene, a type of volatile organic compound (VoC) released from wood resins during kiln drying”

The Terpene issue

Terpene literacy is not as extensive as I would like, but the following report (from 2007) identifies interesting topics: https://www.researchgate.net/publication/271450371_Wood_processing_as_a_source_of_terpene_emissions_compared_to_natural_sources.

"Sawing and lumber drying are equally important terpene emitting processes. Emissions during pellets production can be as important as emissions from sawdust drying, although emissions during drying can also be considerably larger depending on drying technique.

The importance of natural versus anthropogenic emissions depends on the environmental issue. Climate change is global. The importance of the terpene contribution depends on the total amount of emitted terpenes. Natural sources of terpenes would therefore be more important than anthropogenic sources. Formation of photo-oxidants is a regional problem. Terpenes contribute in accordance with their concentration. Hence anthropogenic emissions would be more important. Effects on insects are local, with bark drying an interesting anthropogenic source”

Other reports have been found such as: Underestimation of terpene exposure in the Nordic wood industry - PubMed

Last thoughts

While it seems that “Wood Structure buildings” are being accepted as a general strategy to reduce GWP (and other environmental impacts), other strategies may be required to reduce PoCP.

Formation of ozone of lower atmosphere (PoCP) is measured with kg Ethenee, which contributes in connection with UV radiation to the formation of ozone in the lower atmopshere (summer smog) which is damaging to the respiratory system → not only environmental but also health issue

How do we adress the PoCP impact in CLT buildings?
Is the CLT industry aware of this?
Is there any “low PoCP CLT” available in the market?

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Hello Xavi,
First, I’d suggest you to identify which specific elementary process is contributing to the higher POCP result of the CLT structure considering the dataset you used. In simapro, this is possible using the process contribution function. I also recommend assessing this difference not only in relative values, but also in absolute terms. Just to confirm if it is really associated with terpene emission or not.
Fernanda

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Hello @fbsilva, thanks for your answer!

The process that is contributing the most in higher POCP in CLT is A1-A3:

sankey-diagram-formation
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When checking into the EPD, we can confirm that the specific process most contributing to POCP is “A1:Raw material extraction and processing”:

EPD CLT
EPD CLT1074×427 84.2 KB

Same happens with other EPD from a different manufacturer of CLT:

epd
epd1094×399 65.4 KB

So, we can confirm that the higher POCP in CLT is due to the extraction and process (A1).

This is also demonstrated when checking the difference between the CLT building and the Reinforced Concrete in absolute numbers:

Captura
Captura882×595 77.5 KB

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What It’s hard to confirm with OneClick LCA or with the CLT EPD is the relation between POCP and Terpene, due to the fact that POCP is measured with kg of Ethenee.

The resource I have found to explain why POCP is higher in extraction and processing (A1) of wood products and the relation with Terpene are the reports mentioned:

When I have tried to find out more I really did not come across any other useful information, in fact other info seems to not even list “terpene” into the most POCPs

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The conclusions I have made so far:

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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There are lots of “Carbon Contributing Materials” lists…
but what happens to POCP Contributing Materials?

Just for fun: bellow some POCP results of 1m2 of: CLT, concrete, XPS (insulation), paint and gypsum board. This is a quick exercise to have some results, the functional unit would be 1m2 of material with its own typical thickness

formation-of-ozone-of-lo (2)
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Hi,

I’d be interested to see how this is going also, and we have been working In more Mass timber projects. Also, have you contacted the involved in the extraction process or the processing process to see if they can explain this better and find solutions ? Or has come across some EPDs that may not have this issue.

Thanks

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Hi @Eliana.p , thanks for your message!

I’d say that there are 2 main issues related with CLT I’ve come across so far if compared with a reinforced concrete structure:

  • The first issue was explained in this other post: CLT (kgCO2/m3) similar to CONCRETE (kgCO2/m3) ¿why? - #7 by xramon. In this case I’ve arrived to different conclusions after writing it:

    • Depending on the country this can be an issue or not
    • In the case of Spain the electricity mix before 2020 might impact negatively to the materials that had high electricity consumption during the manufacturing process which is the case of the CLT (because of the drying)
    • Those EPDs that were made using the EN15804 could have different interpretations among the GWP, so if they are updated with the EN15804 + A2 would be better

  • The other issue is what this post explains which is the higher of PoCP if compared with a concrete structure. In this case I’ve not discovered anything new really. Same conclusions as listed above. I’ve contacted some manufacturers and had conversations with them. They are not experts of the LCA so they’ve put me in contact with the assessor that did the LCA. At the same time the assessor can justify that the process they followed was correct and under the stablished procedures. When I asked them about why this and others numbers were higher compared with other EPDs, they said that they didn’t make the other EPDs so they couldn’t answer me… I can imagine that contacting with the involved in the extraction or processing process wouldn’t be that useful. But looking forward to have more feedback so I’d love to hear from you if you find some interesting insides

keep in touch!
thanks!