Comparative Life Cycle Assessment of Mass Timber and Concrete Residential Buildings: A Case Study in China

Round 1

Reviewer 1 Report

In this work, the authors used a developed LCA approach to assess the environmental impacts of different construction materials and concluded that the timber building was better than concrete counterpart, which has guiding significance for policy making. However, the following questions should be addressed.

1. The author uses the LCA model to evaluate the impact of different building materials on the environment. However, the author did not explain the reliability and evaluation bias of the model. The author should explain the applicable conditions of the LCA model and the reliability of the model evaluation results.
2. The conclusion not only includes the author’s key findings, but also concludes key improvements compared to findings in literature and the author’s vision for future work.

Author Response

1. The author uses the LCA model to evaluate the impact of different building materials on the environment. However, the author did not explain the reliability and evaluation bias of the model. The author should explain the applicable conditions of the LCA model and the reliability of the model evaluation results.

 

An additional paragraph was added in the Discussion section to address the limitations of the data and model.

 

1. The conclusion not only includes the author’s key findings, but also concludes key improvements compared to findings in literature and the author’s vision for future work.

 

Additional text was added in the Conclusion section in response to this comment, including a paragraph describing the importance of this study and suggestions for future work.

Reviewer 2 Report

The paper gives a well-presented practical comparison method between the environmental impacts of buildings made of different building materials. However, the insufficient number of prototypes of buildings does not allow us to understand how the conclusions obtained are valid for all types of buildings and structures, or they relate only to a particular building geometry. Therefore, it is necessary to get an explanation in the text of the article in this regard.

Author Response

comment: The paper gives a well-presented practical comparison method between the environmental impacts of buildings made of different building materials. However, the insufficient number of prototypes of buildings does not allow us to understand how the conclusions obtained are valid for all types of buildings and structures, or they relate only to a particular building geometry. Therefore, it is necessary to get an explanation in the text of the article in this regard.

 

Response: A paragraph addressing this comment was added in the Conclusion section. Components described in this study are applicable for many residential buildings and can provide reference to future studies on other types of buildings using mass timber. The outcomes of this case study, including data associated with mass timber manufacturing, energy consumption, and building design may be adjusted to suite various types of buildings.

Reviewer 3 Report

The paper concerns evaluation of the environmental impacts of a timber builiding and a conventional concrete building in China by using a cradle-to-gate LCA model. The analysis also shows how important (reduction in GWP) is the transport (distance) of materials to the construction site.

 

Author Response

Comment: The paper concerns evaluation of the environmental impacts of a timber building and a conventional concrete building in China by using a cradle-to-gate LCA model. The analysis also shows how important (reduction in GWP) is the transport (distance) of materials to the construction site.

 

Response: We appreciate the positive feedback. No changes were made based on Reviewer 3’s comments.

Reviewer 4 Report

The manuscript (ms) discussed a comparison between timber versus concrete as building material in China. Generally, the authors have been presented their research result well, however some clarifications and enhancements are still required in order to improve the ms.

1. In abstract section, GHG emissions should be mention as greenhouse gas (GHG) emissions
2. In introduction section, there was a missing of reason why the authors choose CLT for substituting concrete. There were many ranged of wood products such as glulam (glue-laminated timber), LVL (laminated veneer lumber), plywood, particleboard, fiberboard used nowadays instead of CLT. Authors seemed ignore these products since there were no mentioned in the text. CLT is a new product and still uncommon worldwide. Authors should add more literature review on CLT.
3. In method section, authors should give a brief what of both ISO (literature no.24 and 25) explained. Definition, scope, and method of measurement and calculation. Further, software used should also be mentioned. This is very important because the authors exhibited numeric.
4. Line 227 “picea abies” should be Picea abies
5. Fig.3, why floor in timber building was higher compare to floor in concrete building in term of contribution of global warming potential (GWP)? (42% vs 37%)
6. Fig.4, why insulation in timber building was lower compare to insulation in concrete building in term of GWP? Authors should explain what insulation is. Insulation for thermal or noise. Further, for noise, the insulator function is for absorbing sound or reflecting sound. Wood tends to absorb and concrete tends to reflect sound.

Author Response

The manuscript (ms) discussed a comparison between timber versus concrete as building material in China. Generally, the authors have been presented their research result well, however some clarifications and enhancements are still required in order to improve the ms.

1. In abstract section, GHG emissions should be mention as greenhouse gas (GHG) emissions

 

Corrected.

 

1. In introduction section, there was a missing of reason why the authors choose CLT for substituting concrete. There were many ranged of wood products such as glulam (glue-laminated timber), LVL (laminated veneer lumber), plywood, particleboard, fiberboard used nowadays instead of CLT. Authors seemed ignore these products since there were no mentioned in the text. CLT is a new product and still uncommon worldwide. Authors should add more literature review on CLT.

 

Although there are various types of mass timber products, this case study focuses on CLT. One of the most important reasons for considering CLT in this case study is that CLT can be used as a direct alternative for structural components (e.g., walls and floors), and because it is allowed in mid- to high-rise buildings, which are more common in urban settings, CLT was considered as an appropriate material in this study. This was explained in paragraph 5 of the Introduction section: “It is important to note that one of the advantages of using mass timber over other timber products in construction is that mass timber can be used as structural component in tall buildings. This characteristic can be particularly important for urban areas that have demand for tall buildings due to higher population density”. Additional publications outside of the U.S. were also added in the Introduction section to provide a broader aspect (citations [16], [17], [18], and [19]).

 

1. In method section, authors should give a brief what of both ISO (literature no.24 and 25) explained. Definition, scope, and method of measurement and calculation. Further, software used should also be mentioned. This is very important because the authors exhibited numeric.

 

A description of these ISO standards was added in Section 2. Software and version number were mentioned in Section 2.8 and cited in the References. Database used for the model was also mentioned in Section 2.8.

 

1. Line 227 “picea abies” should be Picea abies

 

Corrected.

 

1. Fig.3, why floor in timber building was higher compare to floor in concrete building in term of contribution of global warming potential (GWP)? (42% vs 37%)

 

Additional explanations are added in Section 3.3.1. to address this comment. In the timber building, the wall and foundation components contributed lower impacts due to the design and material requirements (e.g., lower material mass, lower quantity requirements) different than the concrete building, which in turn, played a less significant role as impact contributors. CLT is the largest impact contributor in the timber building and the floor component used the highest amount of CLT. Thus, the floor component would play a more significant role as an impact contributor in the timber building than in the concrete building.

 

1. Fig.4, why insulation in timber building was lower compare to insulation in concrete building in term of GWP? Authors should explain what insulation is. Insulation for thermal or noise. Further, for noise, the insulator function is for absorbing sound or reflecting sound. Wood tends to absorb and concrete tends to reflect sound.

 

Figure 4 uses the concrete building as the baseline for comparison (100%) and the overall impacts of the timber building was lower (~75%). Because more types of materials were required in the timber building and each of these materials accounted for a certain proportion of the impact, the percentage of contribution from insulation was lower. The insulation as presented in Figure 4 were a part of the wall assembly and served as both thermal and sound insulation. The type of insulation used in the timber building was fiberglass batt, which tends to help absorb sound. A short explanation was added in Section 3.1.

 

Round 2

Reviewer 4 Report

This manuscript is accepted in the present form.