A Lifecycle Assessment of a Low-Energy Mass-Timber Building and Mainstream Concrete Alternative in Central Chile
, Rodrigo Astroza 4, Ignacio González 5, Maureen Puettmann 6 and Mark Wishnie 7Round 1
Reviewer 1 Report
1. Abstract
1) Lines 14-15: the gaps should be briefly introduced in this sentence.
2) Line 15: “environmental benefits” was not appropriate, the authors only discussed the carbon emissions and energy use.
3) the authors used many abbreviations in the abstract, whether they are necessary should be evaluated.
4) both “kg CO2eq per m2” and “kg CO2eq/m2” were used.
2. Introduction
1) the authors should make a review on previous studies relevant to emission assessment of MT buildings as they mentioned in lines 35-37.
2) The knowledge gaps were unclear. Considering that previous studies have already verified that MT buildings can reduce life cycle emissions (lines 35-37), what else is novel about this manuscript?
3. Case Study Building
1) the authors need to evaluate whether the assumed construction site can significantly affect the results of comparison.
4. Materials and Methods
1) lines 154-155, why some phases were ignored, will they lead to considerable impacts on the results?
5. Results
1) why the section No. start from 5.2?
2) actually, the authors only considered several types of primary materials, this fact and potential influences on the results should be clarified in this section.
3) In section 5.4, the authors only listed some results of energy use. However, the reviewer cannot see how the data were obtained and processed, including the transport distance of materials, construction energy use, and operational energy demands. These are all necessary to support the results in the section.
6. Conclusions
1) Line 429, the authors should clarify the aim of this study and the applied method first.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
It is an interesting research work. The authors exclude from the analysis the end-of-life phase of building without any justification. At the end - of - life phase of building some crucial decisions that involve the handling of the retrieved materials (recycling or disposing in the landfill) and affect positevely the environmental benefits, can be taken. I think that the authors have to justify their decision. I would also prefer to have the opinion of the authors (at the end of the paper) on how we can improve further the environmental behaviour of such buildings.
Author Response
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Reviewer 3 Report
1) Please provide a block diagram of the performed LCC analysis step by step
2) what boundary conditions were adopted for the LCC analysis?
3) was the cost and time part deliberately omitted? what was the basic costing in the analysis?
4) what software was used for building visualization? has the model been calculated before? if so, in what program and under what conditions?
I am also sending you a look of durability in the case of pounding of tall buildings in a wooden structure which you can use:
https://www.sciencedirect.com/science/article/pii/S0950061818317458?casa_token=YqyJekfIa_UAAAAA:mQterkc9qAAL-5sCCisQPs75H_A-qgf_CLFwvoJwEBARY6jwftd_AAAmfvirFNIvQd1B0UkT
https://www.mdpi.com/2076-3263/9/12/488
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
Overall, my biggest point of concern is the discussion surrounding the carbon sequestration benefit and potential of mass timber. Your study did not include any end-of-life stages. Therefore, you are taking full benefit of the biogenic carbon sequestration and then implicitly assuming that: 1) all of that carbon remains permanently sequestered and 2) whatever trees were harvested were replaced through sustainable forestry to not lower the total forest biomass. These assumptions need to be made more clear for the reader, as they are major limitations.
In my opinion, you need to rewrite your discussion and parts of the paper that discuss the building being carbon negative due to carbon sequestration of MT. Instead you could discuss how it is only negative until end-of-life, upon which point if any of the materials decompose, are burned, landfilled, or chipped the sequestered CO2 will be released. There are some research papers not referenced here that investigate possible avenues of MT reuse and recycling that enable high rates of carbon retention.
Additionally, the MT described in the study is entirely hypothetical, as Chile does not harvest wood for MT nor does it have a MT plant. So advantages were taken for the MT product by the assumptions made in the study, in terms of proximity to site and energy mix, that are not representative of what is currently possible in Chile. This is fine, but the discussion and conclusion do not make it clear enough that the MT product discussed in the paper is not readily available in Chile. Rather, you would need to source MT from established manufacturers in the US, Europe, and Canada.
Additional discussion and references could be added to provide context about embodied carbon values per m2 for different MT products from the literature, plus emissions associated, or estimated, for transportation of MT from the US, Canada, or Europe.
Lastly, both Figures 1 and 2 have their captions on the next page following the figure. The caption should be on the same page as the figure.
Author Response
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Reviewer 5 Report
In today's era, energy conservation and carbon reduction has become an important issue. The exploration of building energy conservation is of great significance. This article is well organized. The scientific problem of the article is clear. However, similar research problems and methods have been described in a large number of literatures. This paper uses a common research method to solve a specific regional architectural problem. From this point of view, the novelty degree of this paper is general.The following suggestions are expected to help the author improve the quality of the paper.
1.The accuracy of the data provided by the simulation part is not clear enough, which affects the accuracy of the experimental results. The author should display the necessary data of each step of simulation and calculation in the form of tables. Clearly discuss how to use data for calculation and Simulation in each step. Readers can carry out simulation verification according to the method provided by the author, and get the same results. If the simulation process cannot be verified, the authenticity of the data will be reduced. Therefore, the third part should show the calculation process step by step according to the process.
2.The software used for simulating energy consumption shall be introduced in detail. The basic principles and basic simulation parameters of the simulation energy consumption part shall be provided in detail. Otherwise, whether the result is accurate cannot be judged.
Author Response
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Round 2
Reviewer 4 Report
Thank you for incorporating many of the previously mentioned comments. While the revised manuscript reads better, I question the overall carbon values from both buildings, as they are significantly lower than any other study I have seen for MT or reinforced concrete. This could be due to bill of materials differences, system boundary, and other modeling assumptions, but it should be discussed. Especially with regards to the concrete building, many other studies have the embodied emissions associated with concrete buildings well over 300 kg CO2 eq / m2 (Pierobon et al. 2019: 340 kg CO2 eq. / m2 for concrete/CLT hybrid and 450 kg CO2 eq. / m2 for all concrete; Robertson et al. 2012: 420 kg CO2 eq. / m2; Guggemos and Horvath 2005: 550 kg CO2 eq. / m2). Some variability is expected, but your value of 167 kg CO2 / m2 is closer to previous studies on MT than concrete (Chen et al. 2020: 150 kg CO2 / m2 for MT; Allan and Phillips 2021: 167 kg CO2 / m2 for 2 MT buildings; Robertson et al. 2012: 130 kg CO2 / m2).
I would double check your numbers and add additional discussion putting your results into context so readers know your results are on the lower end of the spectrum present in the literature.
Author Response
Thanks for your useful comments. We have doubled checked our numbers, and we confirmed our results. The emissions for the MT and RC buildings are within the lower end of the spectrum presented in the literature (Allan and Philipps 2021; Chen et al 20202; Pierobon et al. 2019). As stated by the reviewer, this is due bill of material differences, system boundary, and other modeling assumptions. As an indication, these differences can be seen with respect to a recent publication by Puettmann et al. (2021), which, as part of the same project commissioned by TNC to the authors, adopts a similar approach by comparing the emissions of six equivalent MT and RC buildings across different regions of the US. For module A1-A5 the results for the US study range from 106 kg CO2eq/m2 to 172 kg CO2eq/m2 for the MT buildings and from 203 kg CO2eq/m2 to 282 kg CO2eq/m2 for the RC buildings. Most of the differences with regards to our study relied on the A4 module, since the materials required for the RC buildings traveled longer distances, generating CO2 emissions as much 55 kg CO2eq/m2 higher. To clarify this specific topic in the revised manuscript, we have included a new paragraph in Section 5.2.2 Construction Stage (A4–A5), page 11 (lines 430– 440).
Reviewer 5 Report
The article has been well improved after revision.
Author Response
Many thanks for your comments
Kind regards
