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Evaluating Fast-Growing Fibers for Building Decarbonization with Dynamic LCA

Sustainability 2025, 17(2), 401; https://doi.org/10.3390/su17020401

by Kate Chilton^1,*, Jay Arehart²

and Hal Hinkle^1,3

Reviewer 1: Anonymous

Reviewer 2: Anonymous

Reviewer 3: Anonymous

Reviewer 4: Anonymous

Sustainability 2025, 17(2), 401; https://doi.org/10.3390/su17020401

Submission received: 10 December 2024 / Revised: 30 December 2024 / Accepted: 3 January 2025 / Published: 7 January 2025

(This article belongs to the Special Issue Fast-Growing, Bio-Based Construction Materials as Key Drivers to a Net-Zero-Carbon Built Environment)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors investigate the use of fast-growing bio-based materials in building frames using the Dynamic Life Cycle Assessment (DLCA) methodology and incorporating actual market product data.

1.The scope of the study is limited to the building product phase modules (A1 - A3), so why not consider the transport, construction and end-of-life (EOL) phases? The U.S. is a vast country and transport distances have a significant impact on carbon emissions.

2.In the introduction, it is clear that the authors do not have enough information on the existing studies and suggest that the authors should look into more studies on CO2 models done by others.See for example "Multi-objective optimal dispatch strategy for power systems with Spatio-temporal distribution of air pollutants"

3.Although studies have shown the advantages of dynamic LCA methods over static LCA in assessing the impacts of biobased carbon, detailed comparative analyses of methods and results with other similar studies need to be included.

4.For the fast-growing wood species studied (e.g. bamboo, eucalyptus, southern Brazilian pine, etc.), while their carbon capture and climate impacts are analysed, why not add other properties (durability, fire resistance) versus traditional building materials?

5.Emission factors are assumed to remain constant throughout the period analysed and do not take into account future grid decarbonisation, changes in fuel sources and manufacturing efficiency improvements.

6.The study mainly analysed building decarbonisation at the technical and material levels, and did not explore in depth the impact of external factors such as policies, regulations and market incentives on the promotion and application of fast-growing bio-based materials.

Author Response

Comment 1. The scope of the study is limited to the building product phase modules (A1 - A3), so why not consider the transport, construction and end-of-life (EOL) phases? The U.S. is a vast country and transport distances have a significant impact on carbon emissions.

Authors’ Response: The purpose of the study was to demonstrate how current carbon accounting standards and reporting metrics are not well suited to enable decision makers to choose materials that will have the best near-term (sub 100 years) impact. Focusing only on the Product phase is more in line with this objective as it highlights the differences in material selection, with a focus on comparing short rotation biogenic materials, long rotation biogenic materials, and non-biogenic materials. While we recognize transport distances can have a big impact on carbon emissions, they vary significantly from producer to producer and build site to build site such that it wouldn’t be a true apples-to-apples comparison given the diversity of materials and their associated sourcing/production locations. For construction phase, there is no readily available public data for the emissions associated with the installation of all the types of framing assemblies assessed. Including transportation (A4) and construction (A5) emissions would be a great example of future extensions of the work. Lastly, while we similarly recognize that EOL has a large impact on the overall impact, our focus was limited to upfront, near-term climate impacts. There are many assumptions associated with EOL emissions modeling, and we wanted to follow as much of a data-driven and precise analysis as possible to highlight the impacts of material selection in the critical near-term. Lines 464-471 are where we explain our rationale in the paper on this topic.

Comment 2. In the introduction, it is clear that the authors do not have enough information on the existing studies and suggest that the authors should look into more studies on CO2 models done by others. See for example "Multi-objective optimal dispatch strategy for power systems with Spatio-temporal distribution of air pollutants"

Authors’ Response: Our objective was to showcase how Dynamic LCAs, in particular, are a better method of assessment in comparison to Static LCAs. While other CO2 models may exist, there would not fit within the strict limits of this study.

Comment 3. Although studies have shown the advantages of dynamic LCA methods over static LCA in assessing the impacts of bio-based carbon, detailed comparative analyses of methods and results with other similar studies need to be included.

Authors’ Response: A detailed comparative analysis of methods and results with other similar studies was out of scope for this study. We do however reference similar studies in Lines 285-287 for the reader to conduct their own comparisons.

Comment 4. For the fast-growing wood species studied (e.g. bamboo, eucalyptus, southern Brazilian pine, etc.), while their carbon capture and climate impacts are analyzed, why not add other properties (durability, fire resistance) versus traditional building materials?

Authors’ Response: We make reference to the other non-climate properties that bamboo and Eucalyptus have as it relates to their use as building materials (Lines 278-280), but that is not the main thrust of the paper. Whole papers have been dedicated to evaluating these properties in comparison to traditional alternatives, and we wanted to keep the focus on the embodied carbon impacts of the material selection.

Comment 5. Emission factors are assumed to remain constant throughout the period analyzed and do not take into account future grid decarbonization, changes in fuel sources and manufacturing efficiency improvements.

Authors’ Response: Correct – we recognize this is a limitation of the study, as noted in Appendix A (Lines 712-715).

Comment 6. The study mainly analyzed building decarbonization at the technical and material levels and did not explore in depth the impact of external factors such as policies, regulations and market incentives on the promotion and application of fast-growing bio-based materials.

Authors’ Response: While an in-depth exploration into the impact of external factors on the promotion and application of fast-growing bio-based materials is out of scope for this study, we agree with the Reviewer on their importance to this topic. As such, we have added Lines 635-645 to the paper.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This is an interesting paper that explores the time value of rapidly growing bio-based materials compared to traditional building materials in the process of global building decarbonization, and it has good innovation. However, there are still some questions that need to be answered:

1. In Section 2, Materials and Methods, the paper directly introduces two new prefabricated framing systems that comply with U.S. building codes, but I believe the reasons for the selection are not clearly explained, which is crucial for the experimental design of the paper.

2. In Section 2, Formula 1 is the probability density function of the normal distribution, but it still needs to provide the meaning of each parameter and explain why σ = μ/2?

3. To enhance the transparency and reproducibility of the research, it is recommended that the authors provide more detailed information about the data sources and parameter selection. For instance, regarding the 2023 North American Material Baselines data from the Carbon Leadership Forum (CLF), it would be helpful to explain how these data were collected and validated.

4.The authors are advised to provide more details on the life cycle inventory data and DLCA model used, such as the model's input parameters, assumptions, and the results of any sensitivity analyses conducted.

5. Section 3 presents the predicted results of the climate impact of four framing systems based on Dynamic Life Cycle Assessment (DLCA). It is suggested that the author should analyze and explain the reasons behind these results in Section 4.

6.It is recommended that the authors consider adding a discussion on the limitations of the study in the conclusion and propose directions for future research. For example, the assumptions used in the study, the uncertainties in the data sources, and how these limitations affect the universality and reliability of the research results.

Author Response

Comment 1. In Section 2, Materials and Methods, the paper directly introduces two new prefabricated framing systems that comply with U.S. building codes, but I believe the reasons for the selection are not clearly explained, which is crucial for the experimental design of the paper.

Authors’ Response: These systems were chosen in order to make the analysis more rooted in reality versus using fictious systems merely to demonstrate a point. We wanted to ensure the systems 1) were already being sold and used by builders to represent real market adoption and 2) had publicly available data in the form of an EPD to conduct the analysis. We note in the conflicts of interest section that the authors of this paper are also associated with the manufacturer of these products.

Comment 2. In Section 2, Formula 1 is the probability density function of the normal distribution, but it still needs to provide the meaning of each parameter and explain why σ = μ/2?

Authors’ Response: The definition of each parameter is described in Lines 401-405. The Reference included in those lines contains further explanation of the formula.

Comment 3. To enhance the transparency and reproducibility of the research, it is recommended that the authors provide more detailed information about the data sources and parameter selection. For instance, regarding the 2023 North American Material Baselines data from the Carbon Leadership Forum (CLF), it would be helpful to explain how these data were collected and validated.

Authors’ Response: The data collection method was quite straightforward for the North American Baselines data – it was pulled directly from the CLF website and reviewed by the Authors to ensure it was appropriate for use in the analysis. The chosen EPDs were confirmed by the Authors and a 3^rd party estimator to confirm they are representative of the materials used in the study’s model building. Lines 363-365 were added to make this clear

Comment 4. The authors are advised to provide more details on the life cycle inventory data and DLCA model used, such as the model's input parameters, assumptions, and the results of any sensitivity analyses conducted.

Authors’ Response: The GitHub repository, listed in the Data Availability Statement, contains this information.

Comment 5. Section 3 presents the predicted results of the climate impact of four framing systems based on Dynamic Life Cycle Assessment (DLCA). It is suggested that the author should analyze and explain the reasons behind these results in Section 4.

Authors’ Response: The first paragraph in the Discussion section (Lines 578-596) is where this explanation is reiterated (in addition to being discussed throughout the Results section). More language was added to further address this feedback.

Comment 6. It is recommended that the authors consider adding a discussion on the limitations of the study in the conclusion and propose directions for future research. For example, the assumptions used in the study, the uncertainties in the data sources, and how these limitations affect the universality and reliability of the research results.

Authors’ Response: Limitations of the study were introduced in Section 2 (Lines 461-471) and elaborated on in the Appendix (Lines 707-739) as they felt more appropriate to include there versus the in the Conclusion. Ideas for future research are included in the Discussion section (Lines 617-620) per the submission template’s instructions.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The article is devoted to the assessment of the carbon footprint of building materials. The problem is urgent, and modeling in this area is important. However, there are no references in the article, the presentation of data is unclear, and there are many common phrases in the work which are not suitable for scientific article. The conclusions are not supported by the results. The tasks and aims of the work are not clear. Nevertheless, the work contains interesting ideas, a good experimental analytical apparatus and an interesting presentation of the results. The article should be revised. Below are my recommendations:

1) There are no Refs. in the article, which is unacceptable 2) The title is very general, it is unclear from the title what exactly is the article about. Also, it is not clear from the abstract which objects are investigated. 3) The abstract should clarify which specific scenarios are being discussed Line 19-20 “The carbon flows for these four framing systems were then scaled across four adoption scenarios…”

In addition, it should be clearly stated in the abstract what is the novelty of the article and the scientific contribution. At the moment, it is unclear what the article gives the reader.

4) Line 34 “policy initiatives and regulations…” Which ones are in which regions and countries? It is desirable to specify too general phrases in a scientific article, based on the facts, giving appropriate references.

5) Line 42 “Broadly speaking, there are two categories of building materials: extractive and biogenic” Is this the opinion of the authors or a generally accepted classification that can be supported by a reference and is it possible to provide exhaustive definitions?

6) Lines 94-148 In the introduction, the authors list the problems in great detail, I recommend shortening this part or presenting the results of this review more concisely. At the same time, the authors do not formulate a specific task that they solve in their work. The purpose of the work and the methods of its solution should be clearly outlined in the introduction. Do the authors analyze the market? Do they propose a new approach to analysis? What are the objects of the work? All this points are unclear.

7) There is no mathematical analysis of the data in the work. And no checking the presented data mathematically.

8) It is also unclear from the conclusions what was counteracted, what specific conclusions were drawn from the conducted modeling. Sections 1, 4, 5 are written in very general phrases.

Author Response

Comment 1. There are no Refs. in the article, which is unacceptable.

Authors’ Response: There are Refs in the article – the list of References starts on Line 741 and there are in-line citations in brackets throughout, per the Submission Template instructions.

Comment 2. The title is very general, it is unclear from the title what exactly is the article about. Also, it is not clear from the abstract which objects are investigated.

Authors’ Response: We have changed the title to “Evaluating Fast-Growing Fibers for Building Decarbonization with Dynamic LCA.” Lines 16-18 in the Abstract tell the reader what is being investigated.

Comment 3. The abstract should clarify which specific scenarios are being discussed Line 19-20 “The carbon flows for these four framing systems were then scaled across four adoption scenarios…” In addition, it should be clearly stated in the abstract what is the novelty of the article and the scientific contribution. At the moment, it is unclear what the article gives the reader.

Authors’ Response: Lines 19-20 list and describe the specific scenarios, which are defined further in the Methods section. Given we are constrained to 200 words in the Abstract, it is difficult to elaborate fully on the novelty of this work (this is done in Lines 245-254). However, we have edited the Abstract to make the key takeaways of the article clearer for the reader.

Comment 4. Line 34 “policy initiatives and regulations…” Which ones are in which regions and countries? It is desirable to specify too general phrases in a scientific article, based on the facts, giving appropriate references.

Authors’ Response: We have clarified in the text that the focus is on the United States and added references to support the claim.

Comment 5. Line 42 “Broadly speaking, there are two categories of building materials: extractive and biogenic” Is this the opinion of the authors or a generally accepted classification that can be supported by a reference and is it possible to provide exhaustive definitions?

Authors’ Response: We have reclassified to biobased and non-biobased and included a reference for the definition of biobased.

Comment 6. Lines 94-148 In the introduction, the authors list the problems in great detail, I recommend shortening this part or presenting the results of this review more concisely. At the same time, the authors do not formulate a specific task that they solve in their work. The purpose of the work and the methods of its solution should be clearly outlined in the introduction. Do the authors analyze the market? Do they propose a new approach to analysis? What are the objects of the work? All these points are unclear.

Authors’ Response: We have gone through the Introduction and made it shorter/more concise where possible. We have also added a ‘scope of work’ paragraph towards the end of the Introduction (Lines 255-267) that clearly outlines the purpose and methods of the study. Regarding analyzing the market, this is outside the scope of work.

Comment 7. There is no mathematical analysis of the data in the work. And no checking the presented data mathematically.

Authors’ Response: The methods used in this study are well-developed in the literature. The Methods section has clearly referenced the studies upon which the mathematical analysis is based (Lines 358-367). For brevity of this manuscript, these methods are left to the referenced studies for the details, and their implementation is included in the GitHub data repository.

Comment 8. It is also unclear from the conclusions what was counteracted, what specific conclusions were drawn from the conducted modeling. Sections 1, 4, 5 are written in very general phrases.

Authors’ Response: We have added additional language to Sections 1, 4 and 5 in order to clarify the introduction and conclusions of the study.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The article Significance of Time Value When Comparing Alternatives for Building Decarbonization is a valuable contribution to the research on sustainable construction, particularly focusing on the dynamic potential of fast-growing biogenic materials.

The study stands out for its innovative focus on the timing of carbon uptake by biogenic materials, a nuance often overlooked in standard carbon accounting methods. By incorporating dynamic life cycle assessment (LCA) modeling to evaluate radiative forcing and global temperature change potential, the authors offer a novel perspective that challenges conventional approaches to carbon neutrality in construction. This originality makes the work a valuable addition to the growing field of building decarbonization.

The article provides valuable insights into the climate benefits of adopting fast-growing biogenic construction materials, such as bamboo and eucalyptus, highlighting their capacity to reduce the climate impact of residential framing systems. The findings have significant implications for policymakers, builders, and sustainability advocates aiming to mitigate climate change within the built environment. The emphasis on scenario-based modeling ensures the content remains relevant under various adoption pathways.

The presentation of the article is of very high quality. The structure is logical and flows smoothly, guiding readers through the background, methodology, results, and implications. The visuals are clear and effective in conveying complex data. This enhances the accessibility of the research to both technical and non-technical audiences.

While the scientific methodology is robust and adequately described, my one concern is the reliance on long-term projections through 2100. While such a timeline is necessary to gauge the full impact of decarbonization strategies, the inherent uncertainties of modeling over such a horizon may reduce the reliability of some predictions. Nevertheless, the research design and methods are well-aligned with the study's objectives, and the authors transparently address these limitations.

The selection of references is very well done, showcasing up-to-date and relevant literature.

The study design is appropriate. The methods are adequately described, though some readers may benefit from additional clarification on the assumptions underlying the adoption scenarios and the temporal dynamics of carbon flows.

The conclusions are consistent with the results and emphasize the urgency of immediate action for achieving climate-cooling benefits, effectively grounding the study's findings in actionable insights.

In my opinion, the article should be accepted in its current form.

Author Response

Comment 1. The article Significance of Time Value When Comparing Alternatives for Building Decarbonization is a valuable contribution to the research on sustainable construction, particularly focusing on the dynamic potential of fast-growing biogenic materials.