Development of an Indicator-Based Framework for a Sustainable Building Retrofit

Abstract

This study develops and operationalizes a multi-dimensional framework for sustainable building retrofit that aligns with national 2050 net-zero objectives. First, we conduct a scoping review of international standards (e.g., ISO), sustainability reporting guidelines (GRI G4), and peer-reviewed studies to define an indicator system spanning three pillars—environmental (carbon neutrality, resource circulation, pollution management), social (habitability, durability/safety, regional impact), and economic (direct support, deregulation). Building on this structure, we propose a transparent 0–3 rubric at the sub-indicator level and introduce the Sustainable Building Retrofit Index (SRI) to enable cross-case comparability and over-time monitoring. We then apply the framework to seven countries (United States, Canada, United Kingdom, France, Germany, Japan, and South Korea), score their retrofit systems/policies, and synthesize results through radar plots and a composite SRI. The analysis shows broad emphasis on carbon neutrality and habitability but persistent gaps in resource circulation, pollution management, regional impacts, and deregulatory mechanisms. For South Korea, policies remain energy-centric, with relatively limited treatment of resource/pollution issues and place-based social outcomes; economic instruments predominantly favor direct financial support. To address these gaps, we propose (i) life-cycle assessment (LCA)–based reporting that covers greenhouse gas and six additional impact categories for retrofit projects; (ii) a support program requiring community and ecosystem-impact reporting with performance-linked incentives; and (iii) targeted deregulation to reduce uptake barriers. The paper’s novelty lies in translating diffuse sustainability principles into a replicable, quantitative index (SRI) that supports benchmarking, policy revision, and longitudinal tracking across jurisdictions. The framework offers actionable guidance for policymakers and a foundation for future extensions (e.g., additional countries, legal/municipal instruments, refined weights).

1. Introduction

Following the Kyoto Protocol (1997) and the Paris Agreement (2015), countries set economy-wide greenhouse gas (GHG) reduction targets. In 2018, the Intergovernmental Panel on Climate Change (IPCC) concluded that pathways consistent with limiting warming to 1.5 °C above pre-industrial levels require achieving net-zero GHG emissions around 2050 [1,2,3,4]. Subsequent high-level convenings—such as the 2019 Climate Action Summit and the United Nations Framework Convention on Climate Change (UNFCCC) Conferences of the Parties—reiterated the urgency of action, and by 2020 many advanced economies had announced 2050 net-zero goals [5,6,7].

Korea likewise declared a 2050 net-zero target and adopted a nationally determined contribution (NDC) to reduce 2030 national GHG emissions by 40% relative to 2018 [8]. Within this, the buildings sector is targeted to reduce emissions by 32.8% by 2030 from the 2018 baseline and by 88.1% by 2050 [9]. From a building life-cycle assessment (LCA) perspective, more than 70% of a building’s GHG emissions occur during the operation phase [10]. Accordingly, since 2020, Korea has mandated Zero Energy Building (ZEB) certification for new buildings exceeding specified size thresholds [11]. Annual ZEB certifications totaled 509 (2020), 1104 (2021), 1266 (2022), 1909 (2023), and 2243 (2024), indicating steady institutionalization of measures targeting operational carbon neutrality [12].

At the same time, building retrofit is increasingly critical, as approximately 40% of Korea’s building stock is 20 years or older [13]. Multiple schemes support energy upgrades in existing buildings; a representative instrument is G-SEED (Green Standard for Energy and Environmental Design), Korea’s national green-building rating system [14,15]. Since 2016, G-SEED has included a Green Remodeling category that provides incentives for retrofitting and is government-operated and administered by the Korea Institute of Civil Engineering and Building Technology (KICT) [16]. However, G-SEED has not been updated since 2016, and retrofit-related policies remain skewed toward energy-saving measures (e.g., insulation reinforcement, high-efficiency equipment replacement, and renewable-energy installation) [15].

These circumstances reveal a gap in comprehensive evaluation frameworks that simultaneously integrate broader environmental dimensions (carbon neutrality, resource circulation, environmental management), social dimensions (habitability, health, safety, regional impact), and economic dimensions (life-cycle cost, performance-linked incentives) [17]. In addition, the absence of a scoring and monitoring system that enables project-level comparability and continuous tracking constrains evidence-based policy decisions among construction-sector stakeholders [18].

This study, therefore, aims to develop a framework for sustainable building retrofit that aligns with the national 2050 net-zero strategy and integrates environmental, social, and economic considerations. We analyze retrofit-related systems and policies in environmentally advanced countries to establish the conceptual basis for sustainable building retrofit and to propose an indicator-based policy approach. Furthermore, we derive an indicator scoring scheme and introduce the Sustainable Building Retrofit Index (SRI) as a quantitative evaluation system. The overall study flow is depicted in Figure 1.

2. Literature Review

2.1. Building Retrofit Research Trends

Retrofit is a series of actions to improve the performance of a building by adding insufficient factors in the manufacturing and construction processes of a building, and terms such as “refurbishment” and “renovation” are used alternately. Retrofit sustainably improves the energy and resource efficiency of existing buildings, which is intended to improve building energy efficiency and service levels to a satisfactory level [19].

According to the UN Agenda for Development and the Sustainable Development Act, the direction of sustainable development in all fields has emphasized the comprehensive consideration of the environment, society, and economy [20,21]. However, research on retrofits has predominantly focused on the operational phase, with a strong emphasis on energy and technology, thus lacking integration of environmental, social, and economic dimensions [22,23,24]. Much of the existing work has been confined to single-issue topics, showing limited linkage to policies that holistically incorporate sustainability considerations [25,26,27,28,29,30,31,32,33]. Furthermore, although some studies—similar to the present one—have analyzed policies and institutional frameworks, they remain largely descriptive and offer only partial recommendations [34,35,36,37,38,39,40,41]. While certain studies have addressed improvements to various retrofit assessment tools (e.g., certification schemes, indicators), they have not sufficiently considered broader sustainability aspects, notably carbon neutrality as a critical issue [42,43,44,45]. In addition, many works are restricted to specific regions, cases, or models, with methodologies overly concentrated on economic feasibility and disconnected from comprehensive sustainability-oriented policy frameworks [46,47,48]. Consequently, there is a lack of research that systematically incorporates environmental, social, and economic dimensions into retrofit policies aligned with national sustainability and carbon-neutral agendas, highlighting the urgent need for further investigation in this area. Building retrofit literature review and this study’s contributions are presented in

Table 1. Building retrofit literature review and this study’s contributions.

Year	Authors	Main Topic	Research Areas and Limitations	Differences in This Study
2023	Ahmed et al. [22]	Sustainability	- Limited number of cases - Short-term data - Weak methodology	- Develops sustainability indicators - Compares policies - Proposes an LCA-based package
2018	Liang et al. [23]
2015	Choi [24]
2025	Sinha et al. [25]	Economic policy	- Sample constraints - Economics-centric focus - Lack of integrated, scalable retrofit evaluation - Limits on factor/policy analysis	- Proposes integrated LCA–regional-impact package - National framework - Integrates metrics and benchmarking - Embeds LCA-based policies
2023	Marchi and Gaspar [26]
2023	Mushafiq and Arisar [27]
2021	Hwang et al. [28]
2019	Bravo et al. [29]
2019	Studer and Rieder [30]
2019	Liang et al. [31]		- Focus on economic incentives - Focus on case-based optimization - Lack of policy metrics	- Integrated retrofit policy - Indicators-based SRI
2018	Mora et al. [32]
2017	Park and Jeong [33]
2025	Go [34]	Renovation	- Analysis of renovation drivers - Lack of integrated sustainability evaluation	- Indicator-based framework - Integrated LCA-linked policy package
2023	Perez-Navarro et al. [35]
2020	Choi [36]
2020	Park [37]
2017	Satu and Ahvenniemi [38]		- Focus on efficiency, barriers, and support - Absence of integrated sustainability indicators	- ISO/GRI-based SRI benchmarking - Beyond energy-only focus
2015	Kim and Youm [39]
2014	Jang et al. [40]
2013	Sim [41]
2025	Barbosa and Almeida [42]	Environmental tool	- Addresses retrofit tools and policies (RP, NSAT, RLMs) - Fragmented standards and environmental bias	- Indicator-based SRI - Identifies Korea’s policy gaps
2023	Pulgar Rubilar et al. [43]
2018	Kim and Yoon [44]
2018	Gonzalez Caceres [45]
2024	Huang and Xu [46]	Framework	- Energy bias and fragmented knowledge - Data/tool gaps and weak contextual adaptation	- Proposes integrated package - LCA-based policy measures
2024	Liu et al. [47]
2015	Malmgren and Mjörnell [48]

.

2.2. Analysis of Pillars and Indicators for Building Retrofit

To develop a sustainable building-retrofit framework, we conducted a scoping review of the literature to derive the three pillars—environmental, social, and economic—and to identify the indicators corresponding to each pillar. The review covered international standards and sectoral guidelines, the GRI G4 sustainability reporting indicators, and peer-reviewed research on retrofit and building sustainability. Specifically, we queried ISO standards using the keywords “sustainability” and “building,” then selected documents applicable to the assessment of cities and buildings [49,50,51,52,53,54,55], to bioenergy sustainability where interactions with the natural environment are relevant [56], and to building services and operations that support sustainable system management [57]. We further examined the GRI G4 framework as widely used guidance for sustainability reporting [58,59,60,61,62], together with studies on the environmental sustainability of retrofit buildings [63,64,65,66] and on material-related differences in building environmental performance [67,68].

For social aspects, we reviewed ISO documents that can be used for building-level social and environmental sustainability [49,50,51,52,53,54,55], standards for radon assessment directly affecting occupants [69,70,71], and people-centered design standards focusing on indoor environmental quality (IEQ) [72,73]. For the economic dimension, we consulted the GRI G4 economic indicators (EC-series) [62,74,75,76,77,78], policy/strategy documents from the Ministry of Environment [79] and the Ministry of Land, Infrastructure and Transport (MOLIT) [80], as well as Castro (2017) on retrofit sustainability in healthcare buildings [81].

To ensure relevance to building retrofit, we screened the above sources for building- and program-level applicability and did not retain GRI items outside this scope—such as sanctions, transport logistics, and investment/market-environment items under EN; pension schemes and management ratios under EC; and labor-practices and product-responsibility items under LA/SO where they are not building-specific. The retained items were then mapped to the three pillars and consolidated into indicator families. Table 2 presents the standards, guidelines, reports, and peer-reviewed research analyzed and summarizes the resulting pillar–indicator structure for sustainable building retrofit.

Within the environmental pillar, we distinguish three indicator families that jointly span energy and non-energy dimensions. Carbon neutrality captures the energy-related drivers of greenhouse-gas reduction—namely, energy-efficiency improvements, electrification, and renewable-energy procurement or on-site generation—and also considers life-cycle greenhouse-gas implications. Resource circulation addresses materials efficiency, recycled content, and the management of construction and demolition waste. Environmental management covers local pollutant control, water and stormwater management, and biodiversity and ecosystem safeguards. In this formulation, energy performance is explicitly treated under carbon neutrality, while the environmental pillar extends beyond energy to encompass broader resource and environmental-quality concerns [49,50,51,52,53,54,55,56,57,58,67,71,72,73].

The social pillar focuses on habitability and indoor environmental quality, on health and safety—including radon assessment and occupant protection—and on regional impact, which captures the building’s interface with the local community and place-based effects during and after retrofit activities. These elements synthesize ISO-based requirements and people-centered standards with practice-oriented guidance that emphasizes in-building social outcomes [49,50,51,52,53,54,55,71,72,73,80,81,82] and are consistent with the literature that separates building-field and environmental domains when structuring social indicators [83].

The economic pillar centers on life-cycle cost (LCC) and on the performance linkage of incentives, reflecting the need to align grants or tax credits with verified retrofit outcomes. Screened GRI EC-series items, government policy documents, and sectoral studies inform the operationalization of these indicators at the building or program level [79,80,81,84]. The consolidated pillar–indicator structure is used as the foundation for the scoring and evaluation scheme in the subsequent sections. Details of the scoping review and the derived pillar–indicator information are provided in Table 2.

Table 2. Details of scope review and derived pillar-indicator information.

Category	Reference		Main Contents	Indicator (1)
Environmental pillar
Standard	ISO 21930:2017	[49]	- Pollution management (water, air, soil)	PM
	ISO 21931-2:2019	[50]	- Managing using energy; recycling water; managing waste treatment; pollution management (water, air, soil)	PM
	ISO 16745-1:2017	[51]	- Assessing carbon emissions	CN
	ISO 21931-1:2022	[52]	- Pollution management (water, air, soil); managing using energy; managing water; using reusable materials	PM
	ISO 21929-1:2011	[53]	- Managing greenhouse gas; using reusable materials; managing waste treatment	CN
	ISO 16813:2024	[54]	- High efficiency of energy facilities	CN
	ISO 37104:2019	[55]	- Managing greenhouse gas; reduce the use of ingredients; using reusable materials; managing using energy; managing water	CN
	ISO 13065:2015	[56]	- Restriction of carbon emissions	CN
	ISO 21401:2018	[57]	- Managing energy; managing water; pollution management (water, air, soil)	PM
Guideline	GRI G4 (EN1-EN2; EN27)	[58]	- Using reusable materials	RC
	GRI G4 (EN3-EN7)	[59]	- Reduce energy consumption	CN
	GRI G4 (EN8-EN10)	[60]	- Reduce the use of water	PM
	GRI G4 (EN10)	[60]	- Recycling water	PM
	GRI G4 (EN11-EN14; EN20-EN22; EN24, EN26-EN27)	[58]	- Pollution management (water, air, soil)	PM
	GRI G4 (EN15-EN19)	[61]	- Restriction of carbon emissions	CN
	GIR G4 (EN23; EN25; EN28)	[62]	- Managing waste treatment	RC
Research paper	Chandrasekaran et al. (2021)	[63]	- Managing waste treatment; restriction of carbon emissions; installation of renewable energy facilities; using reusable materials	CN
	Rinaldi et al. (2020)	[64]	- High efficiency of energy facilities	CN
	Malmgren and Mjörnell (2015)	[48]	- Installation of renewable energy facilities; restriction of carbon emissions	CN
	Zhong and Wu (2015)	[67]	- Using reusable materials; reducing the use of water; managing air pollutants (NOx, PM, VOC, etc.); managing waste treatment	PM
	Mjörnell et al. (2014)	[65]	- Restriction of carbon emissions; reduce energy consumption; managing waste treatment	CN
	Risholt et al. (2013)	[68]	- Restriction of carbon emissions; using renewable energy facilities	CN
	Gohardani and Björk (2012)	[66]	- High efficiency of energy facilities	CN
	Xu et al. (2012)	[69]	- Reduce energy consumption; using reusable materials; high efficiency of energy facilities	CN
	Nguyen, and Altan (2011)	[83]	- Reduce the use of water; managing greenhouse gas; using renewable energy facilities; using reusable materials; recycling water; managing waste treatment	CN, RC, PM
	Anastaselos et al. (2009)	[70]	- Air pollutants (NOx, PM, VOC, etc.) management; reducing energy consumption	PM
Social pillar
Standard	ISO 21931-2:2019	[50]	- Influence of the local ecosystem	RI
	ISO 21931-1:2022	[52]	- Basic environment; influence of the local ecosystem; indoor air quality; lighting; sound insulation	Re
	ISO 21929-1:2011	[53]	- Indoor air quality; safety (durability)	D&S
	ISO 16813:2024	[54]	- Indoor air quality; temperature; sound insulation; lighting	Re
	ISO 37104:2019	[55]	- Influence of the local ecosystem; indoor air quality; harmful substances in the human body	Re
	ISO 21401:2018	[57]	- Influence of the local ecosystem; workers’ industrial safety; safety (durability)	D&S
	ISO 11665-8:2019	[71]	- Air quality (harmful substances in the human body)	Re
	ISO 19454:2019	[72]	- Lighting; temperature; ventilation	Re
	ISO 16817:2017	[73]	- Residential; lighting	Re
Guideline	GRI G4 (SO1-SO2)	[74]	- Influence on the community	RI
	GRI G4 (EN11, EN26)	[75,76]	- Influence of the local ecosystem	RI
	GRI G4 (LA5-LA8)	[77]	- Workers’ industrial safety	D&S
	GRI G4 (LA1-LA4; LA9-LA16)	[62,78]	- Social equity	RI
Report	Newport Partners, LCC (2015)	[82]	- Durability	D&S
	Yoon (2010)	[80]	- Earthquake resistance, durability	D&S
Research paper	Mjörnell et al. (2014)	[65]	- Well-being; citizen’s participation; regional service; social equity; sound insulation; resident safety	RI, Re
	Zhong and Wu (2015)	[67]	- Workers’ industrial safety; sound insulation; durability	D&S
	de Fátima Castro et al. (2017)	[81]	- Social equity; basic environment (sound insulation, lighting, insulation, ventilation, etc.); influence of the local ecosystem; resident safety	RI Re
	Nguyen, and Altan (2011)	[83]	- Resident safety; basic environment (sound insulation, lighting, insulation, ventilation, etc.)	Re
	Xu et al. (2012)	[69]	- Resident safety; residential	Re
	Risholt et al. (2013)	[68]	- Temperature; indoor air quality; durability; humidity	Re
Economic pillar
Guideline	GRI G4 (EC1, EC4)	[84]	- Support; subsidy support	DS
Report	Yoon (2010)	[80]	- Tax deduction; subsidy support	DS
	Ministry of Environment (2003)	[79]	- Improving unreasonable regulations	De
Research paper	Mjörnell et al. (2014)	[65]	- Subsidy support	DS
	Zhong and Wu (2015)	[67]	- Incentive; tax deduction	De
	de Fátima Castro et al. (2017)	[84]	- Incentive; tax deduction; subsidy support	De
	Xu et al. (2012)	[69]	- Incentive	DS
	Risholt et al. (2013)	[68]	- Incentive	DS

⁽¹⁾ Environmental (CN: Carbon Neutrality, RC: Resource Circulation, PM: Pollution Management), Social (Re: Residential, D&S: Durability and Safety), Economic (RI: Regional Impact, DS: Direct Support, De: Deregulation).

Table 2. Details of scope review and derived pillar-indicator information.

Category	Reference		Main Contents	Indicator (1)
Environmental pillar
Standard	ISO 21930:2017	[49]	- Pollution management (water, air, soil)	PM
	ISO 21931-2:2019	[50]	- Managing using energy; recycling water; managing waste treatment; pollution management (water, air, soil)	PM
	ISO 16745-1:2017	[51]	- Assessing carbon emissions	CN
	ISO 21931-1:2022	[52]	- Pollution management (water, air, soil); managing using energy; managing water; using reusable materials	PM
	ISO 21929-1:2011	[53]	- Managing greenhouse gas; using reusable materials; managing waste treatment	CN
	ISO 16813:2024	[54]	- High efficiency of energy facilities	CN
	ISO 37104:2019	[55]	- Managing greenhouse gas; reduce the use of ingredients; using reusable materials; managing using energy; managing water	CN
	ISO 13065:2015	[56]	- Restriction of carbon emissions	CN
	ISO 21401:2018	[57]	- Managing energy; managing water; pollution management (water, air, soil)	PM
Guideline	GRI G4 (EN1-EN2; EN27)	[58]	- Using reusable materials	RC
	GRI G4 (EN3-EN7)	[59]	- Reduce energy consumption	CN
	GRI G4 (EN8-EN10)	[60]	- Reduce the use of water	PM
	GRI G4 (EN10)	[60]	- Recycling water	PM
	GRI G4 (EN11-EN14; EN20-EN22; EN24, EN26-EN27)	[58]	- Pollution management (water, air, soil)	PM
	GRI G4 (EN15-EN19)	[61]	- Restriction of carbon emissions	CN
	GIR G4 (EN23; EN25; EN28)	[62]	- Managing waste treatment	RC
Research paper	Chandrasekaran et al. (2021)	[63]	- Managing waste treatment; restriction of carbon emissions; installation of renewable energy facilities; using reusable materials	CN
	Rinaldi et al. (2020)	[64]	- High efficiency of energy facilities	CN
	Malmgren and Mjörnell (2015)	[48]	- Installation of renewable energy facilities; restriction of carbon emissions	CN
	Zhong and Wu (2015)	[67]	- Using reusable materials; reducing the use of water; managing air pollutants (NOx, PM, VOC, etc.); managing waste treatment	PM
	Mjörnell et al. (2014)	[65]	- Restriction of carbon emissions; reduce energy consumption; managing waste treatment	CN
	Risholt et al. (2013)	[68]	- Restriction of carbon emissions; using renewable energy facilities	CN
	Gohardani and Björk (2012)	[66]	- High efficiency of energy facilities	CN
	Xu et al. (2012)	[69]	- Reduce energy consumption; using reusable materials; high efficiency of energy facilities	CN
	Nguyen, and Altan (2011)	[83]	- Reduce the use of water; managing greenhouse gas; using renewable energy facilities; using reusable materials; recycling water; managing waste treatment	CN, RC, PM
	Anastaselos et al. (2009)	[70]	- Air pollutants (NOx, PM, VOC, etc.) management; reducing energy consumption	PM
Social pillar
Standard	ISO 21931-2:2019	[50]	- Influence of the local ecosystem	RI
	ISO 21931-1:2022	[52]	- Basic environment; influence of the local ecosystem; indoor air quality; lighting; sound insulation	Re
	ISO 21929-1:2011	[53]	- Indoor air quality; safety (durability)	D&S
	ISO 16813:2024	[54]	- Indoor air quality; temperature; sound insulation; lighting	Re
	ISO 37104:2019	[55]	- Influence of the local ecosystem; indoor air quality; harmful substances in the human body	Re
	ISO 21401:2018	[57]	- Influence of the local ecosystem; workers’ industrial safety; safety (durability)	D&S
	ISO 11665-8:2019	[71]	- Air quality (harmful substances in the human body)	Re
	ISO 19454:2019	[72]	- Lighting; temperature; ventilation	Re
	ISO 16817:2017	[73]	- Residential; lighting	Re
Guideline	GRI G4 (SO1-SO2)	[74]	- Influence on the community	RI
	GRI G4 (EN11, EN26)	[75,76]	- Influence of the local ecosystem	RI
	GRI G4 (LA5-LA8)	[77]	- Workers’ industrial safety	D&S
	GRI G4 (LA1-LA4; LA9-LA16)	[62,78]	- Social equity	RI
Report	Newport Partners, LCC (2015)	[82]	- Durability	D&S
	Yoon (2010)	[80]	- Earthquake resistance, durability	D&S
Research paper	Mjörnell et al. (2014)	[65]	- Well-being; citizen’s participation; regional service; social equity; sound insulation; resident safety	RI, Re
	Zhong and Wu (2015)	[67]	- Workers’ industrial safety; sound insulation; durability	D&S
	de Fátima Castro et al. (2017)	[81]	- Social equity; basic environment (sound insulation, lighting, insulation, ventilation, etc.); influence of the local ecosystem; resident safety	RI Re
	Nguyen, and Altan (2011)	[83]	- Resident safety; basic environment (sound insulation, lighting, insulation, ventilation, etc.)	Re
	Xu et al. (2012)	[69]	- Resident safety; residential	Re
	Risholt et al. (2013)	[68]	- Temperature; indoor air quality; durability; humidity	Re
Economic pillar
Guideline	GRI G4 (EC1, EC4)	[84]	- Support; subsidy support	DS
Report	Yoon (2010)	[80]	- Tax deduction; subsidy support	DS
	Ministry of Environment (2003)	[79]	- Improving unreasonable regulations	De
Research paper	Mjörnell et al. (2014)	[65]	- Subsidy support	DS
	Zhong and Wu (2015)	[67]	- Incentive; tax deduction	De
	de Fátima Castro et al. (2017)	[84]	- Incentive; tax deduction; subsidy support	De
	Xu et al. (2012)	[69]	- Incentive	DS
	Risholt et al. (2013)	[68]	- Incentive	DS

⁽¹⁾ Environmental (CN: Carbon Neutrality, RC: Resource Circulation, PM: Pollution Management), Social (Re: Residential, D&S: Durability and Safety), Economic (RI: Regional Impact, DS: Direct Support, De: Deregulation).

3. Materials and Methods

This study aims to propose a sustainable national building-retrofit policy by first establishing a concept of sustainable building retrofit grounded in a systematic analysis of research and indicators across the environmental, social, and economic pillars. On this basis, we conducted a comparative review of domestic and international building-retrofit systems and policies. We then introduced a quantitative 0–3 point scoring rubric for each system and policy and proposed the Sustainable Building Retrofit Index (SRI) to secure comparability across policies and jurisdictions, to enable monitoring over time, and to accommodate policy revisions.

Elements that were insufficient in terms of sustainability in retrofit architecture policies were identified for each country, and a retrofit architecture policy was proposed to supplement such insufficiencies. The framework of this study is shown in Figure 2.

3.1. Development of Sustainable Building Retrofit Concept and Categorization

Drawing on the literature review, we conceptualized sustainable building retrofit across three pillars—environmental, social, and economic—and organized the construct into a three-tier hierarchy of large category (pillar), medium category (indicator), and small category (sub-indicator). Environmental, social, and economic categories were defined as large, and an integrated indicator set was then constructed by assigning the relevant indicators and sub-indicators to each pillar.

Within the environmental pillar, three indicators are specified. Carbon neutrality addresses energy-related greenhouse gas reductions during the operation phase and thus comprises the sub-indicators “High efficiency of energy facilities,” “Installation of renewable energy facilities,” and “Restriction of carbon emissions”; Resource Circulation promotes the recovery and efficient use of resources and includes “Waste treatment,” “Using reusable materials.,” and “Recycling water.”; and pollution management aims to limit emissions and releases across the building life-cycle and therefore consists of “Water pollutant management,” “Air pollutants (NOx, PM, VOC, etc.) management,” and “Soil pollutant management (Oil, fuel, waste, etc.) management.” In this formulation, the environmental pillar explicitly spans both energy and non-energy dimensions.

For the social pillar, the indicators reflect occupant performance, stakeholder safety, and place-based effects. Residential focuses on habitability and indoor environmental quality and is operationalized through the sub-indicators “Social equity,” “Basic environment (Sound Insulation, Lighting, Insulation, Ventilation, etc.),” and “Comfortable environment (Indoor air quality, Temperature/Humidity, etc.)”; durability and safety considers the protection of users and workers and is composed of “Resistance, Durability” and “Workers’ industrial safety”; and regional impact captures externalities on communities and ecosystems through “Influence on the community” and “Influence of the local ecosystem”.

The economic pillar addresses financial feasibility and enabling conditions. Direct support encompasses fiscal instruments for retrofit and therefore uses the sub-indicators “Support, subsidy support” and “Tax deduction,” whereas deregulation facilitates uptake by easing binding constraints and is represented by the sub-indicator “Construction standard relaxation (Volume area ratio, etc.).” The complete list of pillars, indicators, and sub-indicators used for scoring and evaluation is summarized in

Table 3. Defining sustainability for retrofit building policy analysis.

Pillar (Large Category)	Indicator (Medium Category)	Sub-Indicator (Small Category)
Environmental	(1) Carbon neutrality	① High efficiency of energy facilities
		② Installation of renewable energy facilities
		③ Restriction of carbon emissions
	(2) Resource circulation	① Waste treatment
		② Using reusable materials
		③ Recycling water
	(3) Pollution management	① Water pollutant management
		② Air pollutants (NOx, PM, VOC, etc.) management
		③ Soil pollutant management (oil, fuel, waste, etc.) management
Social	(1) Residential	① Social equity
		② Basic environment (sound insulation, lighting, insulation, ventilation, etc.)
		③ Comfortable environment (indoor air quality, temperature/humidity, etc.)
	(2) Durability and safety	① Resistance, durability
		② Workers’ industrial safety
	(3) Regional impact	① Influence on the community
		② Influence of the local ecosystem
Economic	(1) Direct support	① Support, subsidy support
		② Tax deduction
	(2) Deregulation	① Construction standard relaxation (volume area ratio, etc.)

.

3.2. Deriving of Indicator-Based Scoring Framework from Building Retrofit Systems and Policies

This study analyzed seven countries—South Korea and six developed countries (the United States, the United Kingdom, Japan, France, Germany, and Canada)—that implement policies related to building retrofits. To evaluate the alignment between each policy instrument and the study’s sustainable building retrofit concept, we applied a three-level scoring rubric at the sub-indicator (“small-category”) level:

• 3 points (high alignment): the policy satisfies ≥2 sustainability sub-indicators.
• 2 points (moderate alignment): the policy satisfies exactly one sub-indicator.
• 1 point (indirect/minimal alignment): no sub-indicator is explicitly satisfied, but the policy addresses the theme indirectly or in a general manner.

Scores were then aggregated by pillar (environmental, social, economic) and visualized as radar charts to compare the sustainability profiles of each country’s retrofit systems and policies. To inform improvements in Korea, we benchmarked overseas systems and policies that scored strongly on relevant sub-indicators. The country-by-country scoring results across the environmental, social, and economic dimensions are summarized in

Table 4. Domestic and international systems and policies related to retrofitting buildings.

System and Policies	Sustainability (1),(2)
	Environmental			Social			Economic
	CN	RC	PM	Re	D&S	RI	DS	De
South Korea
1. Improving energy efficiency for low-income families	○			●
2. Public building green remodeling support project	●	○	△	●	○		○
3. Green home housing support project	○		○	○			○
4. Green remodeling private support project	●			●			●
5. Building retrofit project (BRP) loan support project	●			○			○
6. G-SEED (Green Standard for Energy and Environmental Design)	●	○		●	○
7. Incentive system related to green building certification							○	○
8. Public Procurement Service, Green Remodeling Order Guidelines	○			●
9. ESCO investment project	●			○			○
10. Green school project	●			○
11. Seoul Dream Housing project				○			○
12. Building Act					○			●
13. Housing Act					○			●
Total of the medium categories	22	4	3	25	8	0	15	8
Total of the large categories	29			33			23
United States (US)
1. Housing Repair and Weatherization	○			●	○		○
2. PACE (Property Assessed Clean Energy) system	●		△	○	○		○
3. Retrofit Chicago	○			○			○
4. Energy Smart Schools Program	○						○
5. SFFW (Single Family Full Weatherization)	○			●			○
6. Single Family ‘Specialty’	○			○			○
7. Multi-family Weatherization	○			○			○
8. Home Repair	○		●	●	○		○
9. Chicago Climate Action Plan	○	○	○	○
10. School Energy Efficiency Project Grant	●			○			○
11. Better Buildings Neighborhood Program	○						○
12. Climate Mobilization Act	○			○			○
13. Built Green	○	○	△	●		○
14. LEED (Leadership in Energy and Environmental Design)	●	●	○	●	△	○
15. NGBS (National Green Building Standard) Certification	○	○		●		○
Total of the medium categories	33	9	9	32	7	6	22	0
Total of the large categories	51			45			22
United Kingdom (UK)
1. BREEAM (Building Research Establishment Environmental Assessment Method)	●	●	○	●	●	○
2. Green Deal	○			○			○
3. Energy supplier efficiency improvement obligation system	○			●			○
Total of the medium categories	7	3	2	7	3	2	4	0
Total of the large categories	12			12			4
Germany
1. CO2 Building renovation program.	●			○			○
2. EnEV (Energy Saving Ordinance)	●			●
3. Energy Efficient Refurbishment	●		○	●			○
4. School of the Future Project	●			○			○
5. ELENA (European Local Energy Assistance)	○						○
6. DGNB (Deutsche Gesellschaft fur Nachhaltiges Bauen)		○	○	●		○
7. EnerPhit	●	○	△	●
Total of the medium categories	17	4	5	16	0	2	8	0
Total of the large categories	26			18			8
Canada
1. HPNC (High Performance New Construction Program)	○	○	○				○
2. Hi-RIS (High-Rise Retrofit Improvement Support)	●		●	○			○
3. HELP (Home Energy Loan Program)	●			○			○
4. Eco-Roof Incentive Program			○	●			●
Total of the medium categories	8	2	7	7	0	0	9	0
Total of the large categories	17			7			9
France
1. PAH (Pretal’ Am elioration de l’ Habitat)	○			●	○		○
2. eco-PTZ (eco-Pret a Taux Zero)	●		△	○			○
3. Plan de Renovation Energetique de l’Habitat	○			○			○
4. Credit d’ impot developpement durable	○			○			○
5. Eco-pret logement social	○			○			○
6. HQE (Haute Qualite Environnementale)	○	○	○	○	○	○
Total of the medium categories	13	2	3	13	4	2	10	0
Total of the large categories	18			19			10
Japan
1. Eco-Flow	●	○		○		○
2. Eco School Plus	○		△			○	○
3. Building Standards Act					○			●
4. CASBEE(Comprehensive Assessment System for Built Environment Efficiency)-Retrofit	○	○	○	●	○	●
Total of the medium categories	7	4	3	5	4	7	2	3
Total of the large categories	14			16			5

⁽¹⁾ Relationship with sustainability: ● (Highly related: 3 points), ○ (A bit related: 2 points), △ (Low relation: 1 point). ⁽²⁾ Environmental (CN: Carbon Neutrality, RC: Resource Circulation, PM: Pollution Management), Social (Re: Residential, D&S: Durability and Safety), Economic (RI: Regional Impact, DS: Direct Support, De: Deregulation).

.

United States. All surveyed systems satisfied the environmental carbon-neutrality criterion. Certification schemes—Built Green, LEED, and NGBS—underpin comparatively higher performance in resource circulation and pollution management via structured requirements for materials selection, waste minimization, and construction-phase controls. Within the social pillar, numerous habitability provisions (e.g., IEQ, occupant comfort) were identified, whereas regional-impact considerations were generally absent. In the economic pillar, instruments were dominated by direct financial support, with performance conditions variably attached.

United Kingdom. Scores were high in carbon neutrality (environmental) and habitability (social), consistent with a lifecycle orientation toward energy and carbon reduction. The BREEAM framework—particularly lifecycle-impact items (e.g., Mat 01)—reinforces assessment beyond operational energy. By contrast, durability, safety, and local/territorial impacts were less explicitly addressed. Economic feasibility was pursued via direct support, yet the Green Deal faced high loan interest and private charges, delivered limited savings and GHG reductions, and was terminated in 2015.

Germany. As in several peers, carbon neutrality and habitability were the most pronounced themes, while durability/safety-focused provisions were not prominent at the national level. Activation relied on direct support alongside EU-linked drivers. The DGNB certification system integrates barrier-free design, emission control, and life-cycle costing (LCC) and—distinctively—assesses regional impacts by considering a building’s effects on the local environment and community context, yielding a more balanced radar profile across environmental and social sub-indicators.

Canada. Carbon neutrality and habitability were dominant, and retrofit uptake was encouraged through direct support. Pollution control was comparatively emphasized, plausibly reflecting multi-pollutant management (including GHGs and criteria pollutants) embedded in Toronto’s retrofit landscape and municipal guidelines. The overall pattern indicates robust environmental compliance paired with consistent occupant-focused social provisions.

France. Carbon neutrality and habitability were addressed at broadly similar levels, accompanied by direct support in the economic pillar. Other themes—resource circulation, pollution control, durability/safety, regional impact, and deregulation—were generally limited. An exception is HQE, which offers an environmental performance-evaluation framework relevant to retrofitting; however, uptake of HQE-aligned requirements within policy tools remained selective rather than comprehensive.

Japan. Scores were comparatively even, with notable emphasis on regional impacts in the social pillar. Outcomes align with policy support for timber use and the prominence of school-building retrofits, where programs such as Eco-Flow and Eco School Plus promote locally sourced materials and the use of schools as educational collaboration spaces, collectively elevating regional-impact considerations.

South Korea. Multiple systems correspond to carbon-neutral items designated by the Ministry of Environment; however, explicit carbon-reduction requirements were comparatively limited over the survey period. Korea pursued emissions measurement through a retrofit-building certification approach. In the social pillar, habitability scored highly; seismic performance and durability are recognized in law as factors related to potential structural defects. By contrast, the social role of retrofit buildings and ecosystem impacts during works were less developed. In the economic pillar, instruments emphasized direct support, whereas deregulatory benefits were limited in scope and depth. Figure 3, Figure 4, Figure 5, Figure 6, Figure 7, Figure 8, Figure 9 and Figure 10 present radar charts that classify each country’s systems and policies against the study’s sustainability framework.

4. Results

4.1. Proposal of Sustainable Building Retrofit Policy

4.1.1. Environmental Policy

To satisfy the sustainable retrofit building systems and policies, policies that satisfied the carbon emission, resource circulation, and pollution control items were required in terms of environmental performance. Therefore, in this study, as a sustainable retrofit building policy in terms of environmental factors, a report on the results of the retrofit life cycle assessment was submitted, which was intended to quantitatively measure the carbon emissions of retrofit buildings from an entire life cycle perspective. In addition, when evaluating the life cycle of a retrofit building, a report on the results of six environmental impact assessments, as well as carbon emissions, was submitted. Air, water, and soil pollutants were measured, and the corresponding values were considered to be available as a standard when establishing policies to limit pollutants to a certain level or less. Life cycle assessment can measure the amount of carbon emissions and other environmental impact emissions from recycling, incineration, and landfilling of buildings during the dismantling and disposal stage by evaluating the environmental impact through the stages of production, construction, operation, and dismantling and disposal of a building. This allows the measures for reducing environmental impact emissions from waste treatment to be considered at the design stage. This supplements the aspect of resource circulation, which shows little interest in waste treatment and the reuse of materials input through building retrofit. Reducing carbon emissions of retrofit buildings by numerically confirming quantitative environmental impact factor emissions and considering the carbon emissions generated during dismantling and disposing of buildings, it is considered helpful in establishing a step-by-step reduction plan.

The life cycle assessment aims to induce the establishment of a plan to reduce the environmental load for each stage of the life cycle by evaluating the information on the environmental load that occurs during the entire life cycle, and is based on this information. The retrofit building life cycle assessment method should be supported in the design stage to help users determine the pros and cons of retrofitting an aging building from a carbon-neutral perspective. Therefore, along with the retrofit building life cycle assessment, it is necessary to set the renovated building and the non-retrofitted or non-renovated building as the standard buildings for the life cycle assessment. The life cycle of renovated buildings was evaluated in the same way as for new buildings. For buildings that have not been renovated or retrofitted, life cycle analysis is performed as in the new building life cycle assessment method by excluding the building materials input for retrofit construction from the calculation of the required amount for the operation stage.

Retrofit restores the performance level of the building to its initial completion without degrading it. The evaluation period for retrofit buildings can be set using the same evaluation period setting method as for new buildings. Major repair retrofitting is set at 50 years, which is the same as the evaluation period for new buildings. As the changed use must comply with the requirements for new use in the use change in retrofit construction, it is set at 50 years, which is the same as the evaluation period for new buildings. The evaluation period of retrofit extension construction is set at 50 years, which is the same as for new construction, because it is structurally designed as a new building in the case of integral extension. The extension department of independent extensions should be set at 50 years in the same way as for new buildings. In an existing building, it is estimated as a building that has not been retrofitted, and the life cycle assessment must be performed by setting the evaluation life to 50-n years (n = construction time–year of completion). As for repair/reinforcement retrofit for construction without reinforcement work, it is not necessary to comply with the requirements for new buildings in the building structure standard, and it is difficult to confirm that the performance of the new construction level has been restored. In this case, the life cycle assessment should be performed by setting the evaluation life to 50-n (n = the time of construction—year of completion). As retrofit construction, with reinforcement construction performed concurrently or independently, meets the building structure standards for new buildings, the evaluation should be performed by setting the evaluation lifespan to 50 years.

As for the retrofit building life cycle assessment, an environmental impact assessment according to the stage of dismantling and disposal of existing buildings should be performed prior to the production stage evaluation, unlike in the new building life cycle assessment. The System boundary of the proposed retrofit building framework in this study is shown in Figure 11.

4.1.2. Social Policies

In this study, as regulations requiring the submission of a report on the analysis results of regional influence factors during retrofit construction may cause the retrofit market to shrink, a policy to support retrofitting in the form of a support project is proposed, as shown in

Table 5. Example proposal of a sustainable building retrofit support program.

Item	Description
1. Project name	- Building retrofit support project in terms of social sustainability
2. Development purpose	- In order to consider the impact of the local community and the ecosystem in the overall retrofitting, such as repair/reinforcement, major repair, change in use, and extension, etc.
3. Operating system	- In retrofit, it is necessary to conduct waste assessment for soil, water, and air pollution according to the use of materials.
4. Support target	- Retrofit construction operators, building owners, public institutions, etc.
5. Support conditions	- Submission of [Community Influencer Report] Whether it is a facility for local residents within the total floor area Whether it affects the quality of life of local residents - Submission of [Report on Factors Influencing Local Ecosystems] Impact of the use of the surrounding land below a certain range due to soil emissions Effect on surrounding water bodies below a certain range from water discharges Ambient atmospheric effects below a certain range from air emissions Protection of surrounding plants during construction - [Maintaining factors affecting the community and local ecosystem] Management of factors affecting the community in retrofit buildings Management of factors affecting the ecosystem after retrofit
6. Support items	- Grants and tax credits [Maintenance of factors affecting local communities and local ecosystems] grant benefits according to the period setting - Allowing materials and equipment above a certain percentage threshold Easing conditions restricting the use of building materials and facilities of a certain grade or higher when submitting a report on the results of analysis of factors affecting the local ecosystem below a certain level

. The “Report on Factors Influencing the Local Community” should include information on whether convenience facilities and rest facilities for local residents have been built together during retrofit construction within the total floor area. Factors affecting the overall quality of life, such as lighting and ventilation for local residents in retrofitted buildings, should be included. In the “Report on Factors Affecting Local Ecosystems,” the evaluation of the extent to which the soil, water, and air pollutants generated during retrofit construction affect the surrounding water bodies and ecosystems should be included. Rather than simply measuring pollutants, this study attempted to consider more social aspects by including the degree of impact on the ecosystem caused by pollutants. For this purpose, it seems that waste evaluation for deriving construction materials and facilities, soil, water, and air pollutants from construction should be performed simultaneously. For smooth policy implementation, research should be conducted to select items to be entered into the regional impact report. In addition, this study proposes to maintain the above-mentioned influence factors of local communities and local ecosystems to ensure continuous management.

4.1.3. Economic Policies

Retrofit policies in the form of subsidies are the most effective way to promote retrofitting buildings and increase the program participation rate. Therefore, this study also intends to support retrofit through direct support and proposes a policy to support retrofit through deregulation in the retrofit market, where various regulations are implemented. The sociality aspect of the retrofit policy proposed in this study (Table 5) was intended to provide sustainable support rather than a one-time payment that provides subsidies when continuously managing local influence factors for a certain period of time. Points are allocated to continuously maintain and manage the influence factors of the local community above a certain level caused by the retrofit building. In terms of factors influencing the local community, in addition to the items described in the sociality policy, items such as continuous use as a resting space for passengers, use as a local community space, and management of use as a children’s experience center or field study site may be included. Furthermore, it is possible to compose and write items to maintain the factors affecting the local ecosystem for a certain period of time after retrofit. Factors affecting the local ecosystem include social policy, continuous identification and management of living organisms in the natural environment around the building, and satisfaction of water quality above a certain level when water quality management is necessary for the management of living organisms. Such factors affecting local communities and local ecosystems are continuously maintained over 5, 10, and 15 years, and when set for a long period of time, more subsidies and tax deductions are provided compared to the short-term. In addition, the analysis result report is submitted under a certain standard condition when submitting the community and ecosystem impact report, and this study intends to propose a policy that allows the use of building materials or facilities that could not be used because of disadvantages in terms of carbon emission during building retrofit at a certain rate. According to the distribution of regional impact and local ecosystem impact factor reports, energy efficiency grade-certified products other than Grade 1, which are generally allowed, can lower the construction cost because of the lower initial purchase cost. This allows retrofit operators to manage and supplement deficient factors in the report rather than simply submitting a report.

4.2. Proposal of Sustainable Building Retrofit Index (SRI)

For the proposed sustainable building retrofit policy to be practically adopted, a quantitative evaluation system is required to ensure comparability among retrofitted buildings and to support consistent monitoring. To this end, we propose the Sustainable Building Retrofit Index (SRI), which enables over-time monitoring and facilitates the identification and remediation of relatively underperforming evaluation items. The calculation procedure is provided in Equation (1).

$$SRI(\%)=(enviScore+econScore+sociScore)÷(enviMax+econMax+sociMax)\times 100$$

(1)

• SRI: Sustainable building retrofit index
• Score: Each pillar attainable points (0–3 per sub-indicator)
• Max: Each pillar’s maximum attainable points (∑ each sub-indicator’s maximum points)

Using the 0–3 point sub-indicator scoring rubric introduced in Section 3.2, we evaluated the seven countries listed in Table 4—South Korea, the US, the UK, Germany, Canada, France, and Japan. The resulting SRI outcomes are reported in

Table 6. Sustainable building retrofit index (sRi) results.

Country	Environmental (1)			Social (1)			Economic (1)		SRI
	CN	RC	PM	Re	D&S	RI	DS	De
South Korea	56.4%	10.3%	7.7%	64.1%	20.5%	-	38.5%	20.5%	27.2%
United States	73.3%	20.0%	20.0%	71.1%	15.6%	13.3%	48.9%	-	32.8%
United Kingdom	77.8%	33.3%	22.2%	77.8%	33.3%	22.2%	44.4%	-	38.9%
Germany	81.0%	19.0%	23.8%	76.2%	-	9.5%	38.1%	-	31.0%
Canada	66.7%	16.7%	58.3%	58.3%	-	-	75.0%	-	34.4%
France	72.2%	11.1%	16.7%	5.6%	22.2%	11.1%	55.6%	-	24.3%
Japan	58.3%	33.3%	25.0%	41.7%	33.3%	58.3%	16.7%	25.0%	36.5%

⁽¹⁾ Environmental (CN: Carbon Neutrality, RC: Resource Circulation, PM: Pollution Management), Social (Re: Residential, D&S: Durability and Safety), Economic (RI: Regional Impact, DS: Direct Support, De: Deregulation).

.

5. Discussion

This study attempted to define sustainable retrofit indicators by analyzing prominent sustainability-related standards, guidelines, and existing studies. In this study, the indicators were defined and applied to analyze retrofit policies. Beyond this analytical role, however, the relevant indicators can also serve as evaluation standards for the sustainability of retrofit practices, covering the environmental, social, and economic dimensions of both building-related fields and policies. By applying these indicators, this study analyzed the building retrofit systems and policies of the surveyed countries to extract their respective strengths and weaknesses in terms of sustainability. This comparative analysis enabled us to determine which dimensions—environmental, social, or economic—are prioritized within each country’s retrofit policy landscape, and it also revealed areas where policy efforts remain insufficient. Furthermore, this study suggests that benchmarking across cases can provide a useful mechanism to address national policy gaps by adapting effective measures from other countries.

To advance this contribution, the framework was refined into a quantitative, index-based metric, the Sustainable Building Retrofit Index (SRI). The SRI transforms qualitative policy principles into measurable, comparable indicators, thereby providing a structured methodology to monitor retrofit policy performance over time. Importantly, the SRI is not presented merely as an abstract framework but as a pragmatic, proof-of-concept instrument that demonstrates how sustainability criteria can be operationalized. By developing the SRI, this study offers policymakers a potential tool to benchmark progress across jurisdictions, identify strengths and weaknesses in existing policies, and ensure comparability in the evaluation of retrofit sustainability. Moreover, the index provides the basis for continuous monitoring, enabling policymakers to track policy effectiveness as revisions, expansions, or new measures are introduced.

At the same time, we acknowledge certain limitations in the current study. The analysis focused on seven countries across three global regions—the Americas (US, Canada), Asia (Korea, Japan), and Europe (UK, France, Germany). These cases were selected based on the presence of well-established, nationally recognized green building certification systems such as G-SEED (Korea), LEED (United States/Canada), BREEAM (UK), CASBEE (Japan), HQE (France), and DGNB (Germany). This ensured that reliable documentation was available and that institutional comparability was possible. Nevertheless, as highlighted by the reviewer, the exclusion of Nordic countries such as Sweden, Finland, Denmark, and Norway is a limitation, as these countries have pioneered energy-efficient building codes, renewable energy integration, and lifecycle-based retrofit policies. Expanding the analysis to include these and other advanced cases would strengthen the extensibility and replicability of the SRI framework.

Another limitation of this study is that it did not examine country-specific legal frameworks or municipal ordinances that directly affect retrofit implementation. While national certification systems provide a strong comparative basis, they do not fully capture the diversity of legal, regulatory, and local policy contexts that shape retrofit practices on the ground. Future research should therefore incorporate national legal systems, environmental regulations, and local ordinances to provide a more comprehensive and context-sensitive evaluation. This is particularly relevant because retrofit policies are often influenced by unique regional conditions such as climate, energy infrastructure, or urban planning traditions. Expanding the framework to integrate these localized factors will not only enhance the precision of sustainability assessments but also improve the relevance of the SRI as a globally applicable tool.

6. Conclusions

This study defined sustainability indicators for building retrofit by analyzing prominent sustainability-related standards, guidelines, and existing studies, and applied them to evaluate retrofit policies in seven countries. Based on this analysis, the following main conclusions can be drawn:

• Definition of sustainability indicators:
  Sustainability in building retrofit was classified into three dimensions—environmental, social, and economic. Within these, the study further identified specific factors: carbon neutrality, resource circulation, and pollution control (environmental); habitability, durability/safety, and regional impact (social); and direct support and deregulation (economic). This framework provides a structured basis for evaluating retrofit policies.
• Cross-national policy comparison:
  The comparative analysis revealed that most countries, except Japan, placed the greatest emphasis on carbon neutrality (environmental), habitability (social), and direct support (economic). However, significant gaps remain, including limited attention to resource circulation, pollution management, and deregulation.
• Findings for South Korea:
  Retrofit policies in South Korea focus primarily on carbon neutrality through the replacement of energy facilities, while resource circulation and pollution control are underrepresented. Legal frameworks ensure durability and safety but insufficiently address regional impacts. Similarly, deregulation mechanisms to enhance economic feasibility are lacking.
• Proposal of the Sustainable Building Retrofit Index (SRI):
  To operationalize the indicators, the study developed the Sustainable Building Retrofit Index (SRI) as a quantitative, index-based framework. This index enables policymakers to monitor and benchmark retrofit policies over time, ensuring comparability across nations and supporting evidence-based revisions.
• Policy recommendations:
  To compensate for insufficient factors, the study proposes (i) conducting life cycle assessments (LCA) of retrofit buildings that explicitly consider carbon neutrality, resource circulation, and pollution control, and (ii) implementing retrofit support programs that require reporting of regional impacts while providing subsidies and regulatory flexibility. These measures can address current policy gaps in both social and economic dimensions.
• Limitations and future research directions:
  The study is limited to seven countries with well-documented certification systems, excluding advanced cases such as Nordic countries, and does not incorporate national legal frameworks or municipal ordinances. Future research should therefore (i) expand the scope to include more countries and local jurisdictions, (ii) integrate more granular datasets (e.g., city-level programs, building-type-specific regulations), and (iii) refine indicator weighting based on regional priorities.

This study presents a multi-dimensional framework for evaluating retrofit policies, develops the Sustainable Building Retrofit Index (SRI) to operationalize sustainability indicators, and proposes policy measures to address identified gaps. These contributions establish a methodological foundation for advancing sustainable retrofit research and provide practical guidance for policymakers. The SRI framework can serve as a basis for cross-country comparisons, be adapted to reflect regional or legal contexts, and be applied to long-term policy monitoring. Through these applications, it has the potential to evolve into a globally applicable tool for assessing and guiding sustainable retrofit policies.