The Environmental Impacts of Façade Renovation: A Case Study of an Office Building

Thank you very much for taking the time to review this manuscript. We would like to thank the reviewer for their valuable feedback and constructive suggestions. Below are our detailed responses to each comment. All changes have been incorporated into the revised manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files. (Note: All revisions made in response to the reviewers’ comments are highlighted in yellow throughout the manuscript.)

Reviewer comments: This study presents a rigorous LCA comparing façade renovation scenarios, with clear strengths in methodological transparency and data-driven conclusions about material performance. However, the paper requires revisions to address critical gaps before publication. First, the exclusion of operational energy impacts significantly limits the real-world applicability of the findings, since energy efficiency is a primary driver for façade retrofits. Second, the reliance on generic LCA data, without site-specific validation or uncertainty analysis, weakens the robustness of the conclusions, particularly in terms of regional relevance. Addressing these issues would enhance the paper’s contribution to sustainable renovation policy-making. Some specific suggestions for improvement are provided below:

Comments 1: The title should be revised to reflect that the study focuses solely on an office building.

Response 1: Thank you for your suggestion. We have revised the title to clearly reflect that the study focuses specifically on an office building, ensuring better alignment with the scope and content of the article.

Comments 2: Given that LCA is a standardized methodology, Section 2.1 (describing basic LCA steps) may be omitted to improve conciseness.

Response 2: Thank you for your observation. In response, we have removed Section 2.1. to improve conciseness. Relevant methodological details have been selectively integrated into Section 2.3. (page 7) to maintain clarity regarding the specific application of LCA in our study.

Comments 3: The authors should provide a clearer justification for selecting these three specific renovation scenarios.

Response 3: Thank you for your observation. We have revised the manuscript to provide a clearer justification for the selection of the three renovation scenarios (Section 2.2., pagse 5-7). These scenarios were chosen to represent a range of realistic renovation strategies with varying levels of intervention, cost, and environmental impact. This selection allows for a meaningful comparison of outcomes and supports the study’s objective to evaluate trade-offs between different renovation approaches.

Comments 4: Figure 7 should be revised to a histogram to better represent the categorical comparison.

Response 4: Thank you for your suggestion. We have revised Figure 7 (now Figure 6, page 12) and replaced it with a histogram to better represent the categorical comparison, as recommended. This change improves the clarity and interpretability of the data presented.

Reviewer comments: In this paper, a life cycle assessment approach was used to investigate the environmental impacts of three façade renovation scenarios for the main building of the Technical University in Zvolen (Slovakia). The analysis focuses on key environmental indicators: ADE, ADF, GWP, ODP, HT, FAE, MAE, TE, POCP, AP. A large amount of design elaboration and data analysis have been carried out, and the environmental protection thinking and application value are very good. The paper has carried out a large amount of data mathematics and analysis work, but there are still too many problems. Specific suggestions are as follows:

Comments 1: The abstract is not concise enough and fails to clearly express the academic goals. The preface fails to focus on clear academic issues and goals. The conclusion is merely a simple superficial understanding, lacking depth in grasping the core points of the research. The topic is quite good, but the research methods and work implementation cannot support the realization of this topic.

Response 1: Thank you for pointing this out. We appreciate the reviewer’s feedback. We agree with this comment. In response, we have revised the abstract to make it more concise and to clearly state the academic objectives of the study. The introduction has been restructured to better highlight the research problem and goals. Additionally, the conclusion section has been expanded to provide a deeper synthesis of the findings and their implications for sustainable renovation strategies. These changes aim to strengthen the academic contribution and clarity of the manuscript.

Comments 2: The thesis is merely a simple case presentation and analysis, as well as a simple scenario analysis. Although numerous test indicators have been selected, there is no unified comprehensive evaluation objective or basis. Section 2.4 should attempt to establish one's own model or, on the basis of predecessors, select certain modified models to clearly identify some intuitive indicators with comprehensive evaluation significance.

Response 2: Thank you for your insightful comment. We acknowledge the importance of a unified and transparent evaluation framework. In response, we have clarified the role of the Composite Environmental Index (CEI) introduced in Section 2.3. by adding a new subsection 2.3.3. (page 10)., which serves as a simplified yet structured model for aggregating multiple LCA impact categories into a single weighted score. Although not a conventional predictive model, the CEI was developed specifically for this study to support intuitive comparison and decision-making across renovation scenarios. Its structure is based on established LCA normalization and weighting principles, adapted to the context of façade renovation. We have revised the section to better explain the rationale, structure, and interpretive value of the CEI as a comprehensive evaluation tool.

Comments 3: The consideration of influencing factors is too limited. There are only three simple scenarios, which are merely the demands of engineering cases and applications. Without delving into both internal and external factors for consideration, it is difficult to consider that a thorough exploration has been achieved and a regular understanding has been formed. Section 2.3 should present the three working conditions in a table for intuitive comparison. For regular understanding, it is necessary to refine the relevant secondary influencing factors and conduct a systematic analysis.

Response 3: We thank the reviewer for this valuable comment. In response, we have revised Section 2.3 to include a new summary table (Table 2, page 6), which clearly presents the key characteristics of all analyzed façade renovation scenarios (A–C and their subvariants). This addition improves the clarity and comparability of the scenarios and supports a more intuitive understanding of the design alternatives. Furthermore, we have added a paragraph acknowledging the current limitation of the study in terms of the number of scenarios and influencing factors (page 5, above Table 2). We emphasize that the selected scenarios were derived from a real-world engineering project and reflect practical constraints. However, we fully agree that future research should incorporate a broader range of internal and external factors—such as building orientation, user behavior, local climate conditions, and material availability—to enable more generalizable conclusions and systematic analysis.

Comments 4: The entire article seems more like a comprehensive evaluation and presentation of simple design work. The cases are rather simple, the methods are not novel, the selection of influencing factors is rather random, and there is a lack of systematic analysis, as well as necessary regular understanding and discussion.

Response 4: Thank you for your critical feedback. The study is indeed based on a real-world renovation project of a university office building, which inherently defines the scope and structure of the analyzed scenarios. While the design configurations may appear simple, they reflect practical constraints and architectural requirements of a historically and functionally significant structure. To address the concern regarding methodological novelty and systematic analysis, we emphasize that the study introduces a Composite Environmental Index (CEI), which aggregates multiple LCA impact categories into a single, weighted score. This approach enhances the interpretability of complex LCA results and supports multi-criteria decision-making. The CEI methodology is aligned with the EU Environmental Footprint framework and represents a structured and transparent evaluation tool.

Furthermore, we have expanded the discussion section to better contextualize the findings and highlight the broader implications of material selection and façade design on environmental performance. We also acknowledge the limitations of the current study and explicitly suggest directions for future research, including the integration of dynamic factors, broader scenario modeling, and socio-economic dimensions. These revisions aim to strengthen the academic contribution of the paper and clarify its relevance beyond the specific case study.

Reviewer comments: The authors studied paper titled “Environmental Impacts of Façade Renovation of a University Building – A Case Study from Slovakia”. The paper is recommended for publication. The following issues may be helpful for the authors to address:

Comments 1: Extend the explanation on the main environmental impacts identified in the facade renovation of the university building.

Response 1: Thank you for your suggestion. In response, we have expanded the relevant sections of the manuscript to provide a more detailed explanation of the main environmental impacts identified through the LCA of the façade renovation scenarios. Specifically, we highlight that Global Warming Potential (GWP), Abiotic Depletion (ADE/ADF), and Ozone Depletion Potential (ODP) emerged as the most robust and decision-relevant impact categories (page 17). These were consistently sensitive to material choices, particularly insulation type and façade finish. For example, scenarios using mineral wool insulation and wood–aluminium windows (Scenario C–2) demonstrated significantly lower GWP and ADE values due to lower embodied energy and reduced reliance on fossil-based materials.

In contrast, scenarios involving aluminium windows and ventilated cladding systems (e.g., Scenario B–2) showed higher impacts in categories such as Human Toxicity (HT) and Terrestrial Ecotoxicity (TE), largely due to the production processes and material composition of aluminium and composite cladding elements.

We also clarified that the Composite Environmental Index (CEI) was instrumental in synthesizing these findings (Subsection 2.3.3, page 10), allowing for a more intuitive comparison across scenarios. The expanded discussion (pages 19-20) now better contextualizes these results and explains how specific material choices influence each impact category.

These additions aim to enhance the reader’s understanding of the environmental trade-offs involved in façade renovation and support more informed decision-making in sustainable building design.

Comments 2: How does the life cycle assessment (LCA) approach contribute to achieving the EU's 200 climate target? Explain that in the manuscript.

Response 2: Thank you for your suggestion. In response, we have added an explanation to the manuscript clarifying how the Life Cycle Assessment (LCA) approach contributes to achieving the EU’s 2050 climate target (in Introduction, page 2 and in Conclusion, page 20). Specifically, we highlight LCA’s role in identifying and reducing greenhouse gas emissions across the entire life cycle of building materials and renovation processes, supporting informed decision-making aligned with long-term climate neutrality goals.

Comments 3: What are the key construction materials used in the refurbishment of the external wall assemblies?

Response 3: Thank you for your question. We have clarified the key construction materials used in the refurbishment of the external wall assemblies in the revised manuscript (Section 2.2., Table 2, page 6). These include thermal insulation materials such as glass wool, mineral wool, and wood-fibre insulation; façade cladding systems such as ventilated cladding (sandstone, Siberian spruce) and plaster finishes; and window infills, comparing aluminium with wood-aluminium frames. The selection of materials was based on their thermal performance, durability, and environmental impact, as assessed through the LCA.

Comments 4: What role does material selection play in optimizing sustainability in the renovation process? Explain that in the manuscript.

Response 4: Thank you for your comment. In response, we have expanded the manuscript (Subsection 2.2. – pages 6-7, Conclusion, pages 21-22) to better explain the role of material selection in promoting sustainability within the renovation process. The revised text emphasizes that thoughtful material selection is a key strategy for minimizing environmental impacts throughout the building’s life cycle. It supports energy efficiency, reduces embodied carbon, and enhances the overall resilience and health of the built environment. Furthermore, the use of the Composite Environmental Index (CEI) strengthens this approach by offering a transparent, aggregated measure of environmental performance, enabling more informed and balanced decision-making.

Comments 5: How do you address the thermal comfort of the building? Have you taken thermal comfort factors into account?

Response 5: Thank you for your question. In response, we have clarified how thermal comfort was addressed in the study (Section 2.2., page 7). While a detailed dynamic thermal comfort analysis was not conducted, we partially addressed this aspect by including the thermal properties of the examined external wall assemblies (Table 3, page 7) in the revised manuscript. We also discussed the expected impact of façade renovation on the building’s heating demand (Table 4, page 7). The renovation scenarios were designed to improve the thermal envelope, which contributes to more stable indoor temperatures and reduced energy consumption for heating—factors that are closely linked to thermal comfort. These improvements are in line with national energy performance requirements and support occupant well-being.