A Bibliometric Analysis and Scoping Review of the Critical Success Factors for Residential Building Energy Retrofitting

Abstract

Retrofitting existing residential buildings presents a feasible approach to improving energy efficiency. Therefore, recognising the critical success factors (CSFs) for residential building energy retrofitting (BER) has remained a significant topic in this climate change era. However, given the fragmented nature of past findings, this study reviewed past studies on the CSFs for residential BER. Utilising Arksey and O’Malley’s framework, 138 studies were initially examined, with 33 meeting the inclusion criteria and synthesised according to the PRISMA-ScR guidelines. The review started with a bibliometric analysis, including publication trends, types, geographical focus, etc., and found growing interest in this topic amongst authors in China, Germany, Saudi Arabia, the UK, and Europe. The scoping review results highlight seven overarching themes of CSFs: project-, contract-, stakeholder-, team-, financial-, regulation-, and material/technology-related. Notably, the most emphasised across the studies were stakeholder-, project-, regulation-, and financial-related CSFs. A further review of the included studies revealed that the dominant methods used in past studies were factor analysis, regression analysis, social network analysis (SNA), and structural equation modelling (SEM). This study provides valuable insights for regulatory bodies, construction professionals, project managers, and homeowners seeking to develop customised retrofitting solutions, advancing residential BER research and practice. Further research is suggested to understand how combinations of factors can drive retrofitting success across varied contexts.

1. Introduction

As global efforts intensify to address climate change issues, the construction industry holds a significant position in the imperative to reduce its carbon footprint and achieve the Sustainable Development Goals (SDGs), specifically those focused on affordable and clean energy (SDG 7), sustainable cities (SDG 11), and climate action (SDG 13) [1]. This imperative is further amplified by the pledges made by 197 countries in the Paris Agreement, which aims to limit the global temperature rise to 1.5 °C [2]. Demonstrating commitment to their pledges, 124 countries have initiated plans to achieve carbon neutrality between 2040 and 2070 [3,4,5,6], highlighting the urgent need for effective carbon reduction strategies.

Within this context, improving the energy efficiency of existing buildings has become a critical pathway to carbon neutrality, especially considering that 80% of today’s buildings will still be in use by 2050, and recovering the energy loss consequent to demolishing and replacing them with new sustainable ones could take over 65 years [7,8]. This reality underscores the significance of retrofitting as a desirable alternative for reducing energy consumption in existing buildings. According to Tan et al. [9], building energy retrofitting (BER) refers to upgrading building components to enhance the environmental performance. BER has several benefits, which include a 30–40% reduction in energy consumption and over 50% reduction in carbon emissions [10]. BER also increases property values by 13.5% and lowers operational costs by 15–62% [11,12]. Beyond economic advantages, it improves indoor comfort, reduces healthcare costs, creates job opportunities, and guarantees socio-economic development [13].

Given the complexity of its impacts, identifying the critical success factors (CSFs) for BER has become a growing area of research. Several empirical studies have provided useful insights into different CSFs for BER, but their findings appear fragmented in contexts such as the residential typologies, regions/climatic conditions, and methodology. First, different residential building types, ranging from single-family detached homes to multi-unit apartment complexes, can be retrofitted. Unlike studies that considered specific residential types [14,15], this review provides a comprehensive and inclusive analysis of critical success factors across diverse residential building typologies. The focus on residential buildings is given by their direct connection to human daily lives and comfort [16]. According to Liang et al. [17], residential buildings account for over 80% of the total energy consumption during their operational phase. While this building type often encounters specific challenges related to BER requirements, only a few studies have examined the CSFs for residential BER [15,18,19,20].

Scholars have explored diverse aspects of residential BER, including the development of digital tools and processes for planning retrofits [15,21], market dynamics, stakeholder rights, and homeowners’ willingness to invest in retrofitting [22,23,24,25], stakeholder behaviours, participation, and interactions in retrofit projects [20,26,27,28], and technical and environmental assessments of energy-saving initiatives and retrofit strategies [19,29,30,31]. The areas focused on also include strategic approaches for sustainable urban development and optimising retrofit processes [32,33,34], region-specific retrofitting challenges across different climatic contexts [35,36,37], innovative methods utilising data analysis and artificial intelligence [38,39], and comprehensive literature reviews to outline research directions and pinpoint CSFs in BER [40,41,42].

Second, the impact of retrofitting solutions relies on a thorough understanding of various environmental and socio-economic contexts [43]. For instance, in temperate regions, the focus is on optimising the thermal envelope and utilizing a passive solar design, while in hot and humid areas, the emphasis is on reducing cooling loads and managing humidity [44,45]. In colder climates, there is a need for high levels of thermal insulation and efficient heating technologies [46], such as building management systems, smart sensor networks, and integrating renewable energy sources like rooftop solar panels, micro-combined heat and power systems, and smart energy storage solutions [47,48]. These technological advancements should be supported by economic models that offer flexible financing options, engage stakeholders, and align with changing regulatory requirements [43]. Valdiserri et al. [49] argue that the climatic zone of a building’s location could strongly affect its retrofit investment payback period. This necessitates an interdisciplinary approach to harmonise technical expertise with social adaptability and transform existing buildings into efficient and resilient infrastructures that significantly reduce carbon emissions and contribute to global sustainability objectives [50,51].

Third, data analysis methods such as factor analysis, regression analysis, social network analysis (SNA), and structural equation modelling (SEM) have dominated the past literature (see [25,27]). However, these methods possess significant limitations that make them inadequate for measuring the CSFs for residential BER. For example, regression and factor analysis often neglect contextual variations and oversimplify complex interactions with an assumption of uniform significance across factors [52,53]. SEM relies on pre-defined linear models that do not capture the nuanced interdependencies between CSFs. SNA focuses too narrowly on network structures without addressing how CSFs operate in diverse combinations [54]. Given these limitations, Fischer [54] suggests alternative approaches such as Fuzzy-set Qualitative Comparative Analysis (fsQCA) in analysing CSFs. Unlike traditional methods, fsQCA focuses on the logical connections between combinations of causal conditions that might lead to successful outcomes across varied contexts [55,56], thereby providing deeper insights into the complex relationships between CSFs [57].

Lastly, there is a lack of scoping reviews that consolidate the CSFs for residential BER. Against this backdrop, this study distinguishes itself from previous studies by synthesising current research findings on the CSFs for residential BER and examining how those studies analysed the CSFs, providing clear directions for future research. To achieve these, three research questions are important: (a) What are the bibliometric characteristics of the selected studies on the CSFs for residential BER? (b) What are the key themes of CSFs for residential BER implementation? And (c) what methodology does the existing literature adopt in analysing CSFs for residential BER? By answering these research questions, this study offers several benefits to multiple stakeholders, including homeowners, contractors, government agencies, and energy service providers, not only in understanding the CSFs, but also in making the best decision in the implementation of residential BER towards the achievement of net-zero emissions and SDGs. It also provides clear directions for future research.

The remaining parts of this paper are structured as follows. Section 2 outlines the methodology used in selecting the reviewed studies. Section 3 summarises the results of the bibliometric analysis and scoping review of selected studies, while Section 4 discusses the implications for policy and research. Lastly, Section 5 provides the conclusions and limitations of the study.

2. Materials and Methods

Several frameworks can be used for literature reviews. These include systematic reviews [58,59], meta-analyses [58], integrative reviews [60], bibliometric analyses [56], and scoping reviews [59,61]. This study began with a bibliometric analysis of the selected studies on the CSFs for residential BER and proceeded with a scoping review.

2.1. Bibliometric Analysis

A bibliometric analysis was used to chart the data obtained about the selected studies [62]. This method helps to analyse the impact of the studies based on different criteria including countries, subjects, and keywords. The analysis was aided by MS Excel^® (Office 16, Microsoft Corporation, Redmond, WA, USA) and VOSviewer (version 1.6.20, Centre for Science and Technology Studies, Leiden University, Leiden, Netherlands) with which visual representations of scientific landscapes in co-authorship and authors’ keyword co-occurrence were generated. It also shows the association strengths (proportion of total co-occurrences of authors’ keywords) between similar keywords which were derived [63].

2.2. Scoping Review

In the review of the past literature on the CSFs for residential BER, Arksey and O’Malley’s framework (developed in the University of York, Heslington, York, UK) [61] was employed for several reasons. First, unlike systematic reviews which focus on narrow research questions and require high-quality empirical studies, Arksey and O’Malley’s framework [61] allows the broader literature coverage necessary for mapping this emerging field where evidence is scattered across various sources [59]. The meta-analysis requires homogenous studies with comparable quantitative data, whereas the literature on the CSFs for residential BER is multifaceted. Similarly, integrative reviews lack the systematic approach needed for comprehensive literature mapping [60].

While Arksey and O’Malley’s framework [61] provides methodological rigour through its iterative and flexible approach, its reporting guidance is limited, hence the use of the PRISMA-ScR reporting guidelines. This integration particularly suits the research questions as it enables the systematic identification and documentation of CSFs while ensuring the transparent reporting of methodological approaches in the existing literature [64].

We also used fsQCA software (version 3.0, University of California, Irvine, CA, USA) to demonstrate the use of fsQCA in the analysis of CSFs.

2.2.1. Definition of Research Questions

The first stage of Arksey and O’Malley’s framework [61] is the definition of the research questions stated earlier. This framework allows open-ended questions that can be answered by synthesising past studies’ findings across several contexts [61]. Specifically, our literature search revealed a diverse range of perspectives present in the existing literature, leading to the emergence of recurring patterns and themes.

Following Arksey and O’Malley’s iterative approach, we refined the question to align with these themes while keeping it broad enough to include various study types and geographical contexts. This refinement process allowed us to map established factors and pinpoint knowledge gaps for future research. By promoting the inclusion of studies with different methodological approaches, the framework ensured that the question remained adaptable, reflecting how CSFs for residential BER were analysed across different countries and regions. This inclusivity facilitates a meta-aggregative synthesis through systematic collation, categorisation, and results’ summarisation in a way that maintains the original meaning of the data [65].

2.2.2. Literature Search Strategy

After defining the research questions, we conducted an extensive literature search from three databases (Scopus, Web of Science, and Google Scholar) in September 2024, using different keywords (See

Table 1. Keywords and search strings.

Database	Keywords and Search Strings
Scopus (32)	(ALL(“energy retrofitting” OR “energy-efficient retrofitting” OR “energy retrofit” OR “deep energy retrofit” OR “sustainable building retrofit”) AND TITLE-ABS-KEY (“residential buildings” OR “housing” OR “dwellings” OR “residence”) AND TITLE-ABS-KEY (“critical success factors” OR “csf*” OR “success factors” OR “key factors” OR “enablers”)) AND (LIMIT-TO (LANGUAGE, “English”))
Web of Science (11)	ALL = (building retrofit*) AND ALL = (“residential buildings” or “dwellings”) AND ALL = (“key factor” or “success factors” or “critical success factors” or enablers) AND ALL = (energy retrofit*)
Google Scholar (67)	“Critical success factors” and “residential buildings” or “homes” or “housing” and “energy retrofit*”
Additional literature found via Google search (28)	What are the CSFs for building energy retrofit implementation?

). We also reviewed the reference lists of selected articles and further searched for more pertinent publications on Google. Due to the evolving nature of this research area, we did not restrict our literature search to any specific range of publication years. The search yielded 138 publications comprising academic journals, conference proceedings, and a thesis. These publications were exported to MS Excel^® for further screening.

2.2.3. Screening and Selection of Past Studies

The screening and selection process was designed to ensure the systematic and unbiased identification of the relevant literature on the CSFs for residential BER. To mitigate potential bias, we established objective inclusion and exclusion criteria for all potential studies. The selection criteria were designed to eliminate subjective decision making by creating transparent guidelines that consider the application of a uniform and rigorous screening process to every potential study and using objective metrics such as the research focus, methodological approach, and publication type.

Table 2. Inclusion and exclusion criteria.

Inclusion	Exclusion
Studies focused on residential BER.	Studies not focused on residential buildings.
Studies that analysed CSF (quantitatively or qualitatively, or mixed methods).	Research focused solely on different aspects of BER (e.g., energy conservation, energy efficiency, cost analysis) without a clear emphasis on CSFs.
Studies conducted in different climates, but focused on residential buildings.	Viewpoints and editorials that lack empirical data or systematic analysis related to CSFs.
Studies whose full texts were available online to ensure comprehensive data extraction.
Studies written in the English Language.

shows the information on the criteria considered for including and excluding studies in this review.

2.2.4. Data Charting

Following the screening and selection of past studies, we charted the selected articles. Arksey and O’Malley [61] describe data charting/mapping as a technique for synthesising and interpreting qualitative data. We confirmed and extracted relevant articles based on the author/publication year, research focus, region/country of origin, methodology, key results, and identifiable CSFs (see

Table 3. Characteristics of reviewed articles.

S/N	Publication	Publication Type	Research Purpose	Region/Country of Origin	Research Method	Results
1	Armijo et al. [21]	Conference paper	To describe the use of the OpenBIM approach in transforming stakeholders’ implicit knowledge for automation into an OpenBIM digital process that adheres to Building Information Modelling (BIM) standards.	Europe	Qualitative (clustered, randomised community-based trial)	Insulating homes reduces health disparities in communities with low incomes by improving indoor temperatures and health outcomes.
2	Galvin [22]	Journal article	To investigate if rental and sales markets discourage property owners from upgrading their apartments to meet strict energy efficiency requirements.	Western Germany	Quantitative (evolutionary game theory)	Apartment owners who convert their properties frequently discover that, unless they receive a subsidy, sales premiums for energy efficiency do not cover retrofit expenses, and purchasers must pay higher purchase prices that are not entirely offset by energy savings. Landlords recoup only a fraction of retrofit costs through rental premiums, but tenants may balance higher rents with lower energy bills.
3	Gaspari et al. [15]	Journal article	To provide Social Housing Companies with a useful and time-saving tool to help them plan maintenance and retrofit projects for the diverse and large number of buildings they manage.	Italy	Mixed methods	Inaccuracies in energy performance estimates generated using the fast approach are acceptable since social housing managers save a significant amount of money, time, and effort during the planning stage. Simulations shows the potential improvements that could be achieved by applying different scenarios to the entire stock.
4	Groh et al. [23]	Journal article	To determine whether energy efficiency commands a higher price in the German rental market.	Germany	Quantitative	Current regulations, including the CO2 tax, do not sufficiently compensate landlords for retrofit costs. The marginal costs outweigh the marginal benefits by far.
5	He et al. [27]	Journal article	To investigate the factors affecting residents’ intentions to green retrofit existing residential buildings.	China	Quantitative	Subjective norms and perceived behavioural control are two factors that directly and significantly affect residents’ intentions. Though it does not directly impact intentions, the concept of green retrofitting indirectly affects them through behaviour and subjective norms. The biggest influence comes from policy issues, both directly and indirectly through perceived behavioural control. Demographic characteristics and regional differences show significant variations in influence paths.
6	He et al. [66]	Journal article	To develop a cost-effective decision-making model for building retrofits suited to the varied and temperate climate regions of China.	China	Mixed methods	In temperate zones, key measures include lighting upgrades, wall insulation, and better window glazing. In hot summer–cold winter zones, additional upgrades like heating systems and shading devices are crucial. A total of 40% energy saving can significantly reduce energy use by approximately USD 1.30 to 3.20 per m2/year.
7	Howden-Chapman et al. [67]	Journal article	To describe the purposes and procedures of a clustered, randomised, single-blinded study on the health effects of insulating existing homes.	New Zealand	Quantitative (clustered, randomised community-based trial)	Complex environmental interventions may be robustly tested in large-scale trials with high participation rates.
8	Huang and Lin [24]	Journal article	To evaluate the rights and interests of stakeholders as well as the influencing factors.	China	Quantitative (evolutionary game theory)	The study highlights the best strategies for stakeholders, emphasising the role of government subsidies and fines in encouraging collaboration and involvement in energy-saving retrofitting.
9	Huang et al. [25]	Journal article	To examine the factors influencing the willingness of homeowners to invest in building retrofitting.	China	Mixed methods (interviews and survey)	Financial incentives, environmental knowledge, and perceived advantages were all significant factors in determining investors’ willingness.
10	Hwang et al. [68]	Journal article	To evaluate the probability, impact, and criticality of green building construction projects to determine the primary factors influencing their productivity and compare them to conventional projects.	Singapore	Mixed methods (literature review, interviews, and survey)	Workers’ experience, technological design modifications, workers’ skill level. Green building initiatives are more productive than regular projects due to better planning and work scheduling.
11	Jagarajan et al. [40]	Journal article	To examine the body of research on green retrofitting, pinpoint current research directions, and emphasise the barriers and CSFs necessary for green retrofit projects to be implemented successfully.	Not specified	Qualitative (systematic literature review)	Stakeholders’ engagement, technological advances, and policy support are critical to successful green retrofit implementation.
12	Jia [37]	Thesis	To determine and reduce the hazards associated with household energy retrofits in China’s hot summer and cold winter regions.	China	Quantitative (Transaction Costs Theory)	The study identifies financial, organisational, and technological risks and proposed risk reduction methods, emphasising the need for government assistance and effective project management.
13	Krarti et al. [29]	Journal article	To assess the environmental and economic impacts of energy-saving initiatives for existing and new buildings.	Saudi Arabia	Quantitative (bottom-up analysis)	The study emphasises the relevance of government regulations and incentives for encouraging private-sector investment in energy-saving measures.
14	Liang et al. [17]	Journal article	To develop a set of CSFs for energy efficiency retrofit projects and examine how stakeholders and CSFs interact.	China	Qualitative (SNA and stakeholder analysis)	The five significant CSFs for managing green retrofit projects are stakeholder cooperation, policy support, cost, technology, and information sharing.
15	Liu et al. [26]	Journal article	To assess the influence of public participation on residential buildings’ energy-saving retrofits.	China	Mixed methods	Public participation before, during, and after retrofitting results in greater energy savings.
16	Madushika and Lu [41]	Journal article	To review the current state of green retrofitting in developing economies and suggest future research directions to enhance its application.	Developing economies (with a focus on countries like China, Malaysia, and Egypt)	Mixed methods (scientometric and content analyses)	The study suggests five key topics for future research in developing countries: performance evaluation, performance optimisation, adoption, regulations and incentives, and stakeholder involvement.
17	Martin et al. [33]	Journal article	To optimise and schedule residential building retrofits as efficiently as possible to achieve several policy objectives.	Not specified	Quantitative (SHAPE model)	The study emphasises the significance of strategic planning as a decision-support tool for stakeholders in informed decision making on retrofit measures.
18	Mejjaouli [34]	Journal article	To provide a comprehensive framework for building retrofits that will result in zero-energy buildings.	Saudi Arabia	Quantitative (mathematical programming, simulation, and the Analytic Hierarchy Process)	The framework’s application results in a retrofitting plan that achieves 30% annual energy savings and has a 2.2-year payback period.
19	Monna et al. [31]	Journal article	To analyse energy simulation to evaluate the possible energy savings from a proposed retrofitting programme for typical existing residential buildings.	Palestine	Quantitative	The results suggest significant energy savings from the retrofitting measures. Level one measures resulted in a 19-24% decrease in energy consumption. Combining levels one and two led to a 50–57% reduction, while implementing all three levels achieved a 71–80% decrease in total energy usage for heating, cooling, lighting, water heating, and air conditioning.
20	Mukhtar et al. [30]	Journal article	To evaluate the economic, environmental, and technical benefits of installing heat pump systems in existing housing stock to increase energy efficiency and conservation.	Cyprus	Quantitative	The retrofit project resulted in considerable energy savings, lowering electrical energy consumption for heating/cooling systems by 144,825 kWh annually and CO2 emissions by 121,592.8 kg annually. The economic study determined that the retrofit was feasible.
21	Ohene et al. [35]	Journal article	To investigate the feasibility of constructing net-zero energy buildings in tropical regions.	Ghana	Quantitative (parametric simulation)	Passive design strategies, such as natural ventilation, sun-shading, daylighting, and envelope airtightness, can significantly reduce building energy use intensity by 48–50%.
22	Pardo-Bosch et al. [32]	Journal article	To investigate significant aspects of building retrofitting for strategic sustainable development of cities.	European cities (Nantes, Hamburg, and Helsinki)	Qualitative	The integration of customer interface, funding and public–private–people partnership approach is key to scale up.
23	Peel et al. [14]	Journal article	To investigate the enablers and barriers to energy efficiency retrofitting of social housing.	UK	Mixed methods (interviews and surveys)	The study identifies seven categories of barriers and enablers: financial matters, technical issues, information technology, government policy and regulation, social factors (including awareness of the energy efficiency agenda), quality of workmanship, and disruption to residents.
24	Sang and Yao [18]	Journal article	To assess and identify the impact of CSFs on the development of green housing projects.	China	Quantitative	The study identifies five categories of CSFs: management factors, technical capacity factors, financial constraint factors, resource factors, and policy and regulatory factors.
25	Shen et al. [20]	Journal article	To identify CSFs and develop a collaborative governance mechanism for transforming existing residential buildings in urban renewal schemes.	China	Quantitative (SNA)	The study emphasises the importance of collaborative governance, proposing nine governance mechanisms based on the relationships between 13 CSFs and their respective stakeholders.
26	Soulios et al. [69]	Conference paper	To evaluate the interior insulation systems’ hygrothermal performance in upgrading a historic building.	Denmark	Quantitative (hygrothermal simulations)	Adding internal insulation increased the moisture content in the original masonry walls, which implies a higher risk of moisture-related damage such as mould growth, frost damage, and interstitial condensation.
27	Su et al. [42]	Journal article	To review the state-of-the-art in building energy research and determine directions for future developments.	Not specified	Qualitative (literature review)	Most studies focused on energy analysis and conservation, including energy models for prediction, the impact of resident behaviour, building forms, and renewable energy utilisation.
28	Wang et al. [19]	Journal article	To develop the best possible energy-saving retrofit plans for older homes.	China	Quantitative	The optimal retrofit scheme can reduce energy consumption by 18.52% in the targeted residential buildings, resulting in total energy savings of approximately 260.43 GWh.
29	Wenninger et al. [38]	Journal article	To investigate the use of socio-demographic data and explainable artificial intelligence (XAI) for understanding and improving residential BER practices.	UK	Quantitative	The critical factors influencing retrofitting decisions are building age, energy performance ratings, and the socio-economic status of residents.
30	Wierzba et al. [39]	Journal article	To develop a proactive approach that encourages the use of audit data throughout neighbourhoods to maximise the impact of residential building energy audits.	US	Quantitative	Investing USD 146,500 in retrofits could save 9.1 million kBtu of energy annually, reduce utility costs by USD 64,000, and cut 555 US tons of greenhouse gas emissions. Targeting older neighbourhoods benefits low-income families and strengthens community ties. This cost-effective approach supports policy initiatives for neighbourhood renewal and energy management.
31	Wu et al. [36]	Journal article	To assess the feasibility of retrofitting existing residential buildings in Guilin, China, to satisfy the EnerPHit standard—a certification for energy-efficient building retrofits.	China	Quantitative	Retrofitting residential buildings in Guilin, China, to the EnerPHit standard can reduce energy consumption by up to 60%. Despite high initial costs, the long-term savings and environmental benefits make it worthwhile.
32	Xie and Liu [70]	Journal article	To analyse stakeholders’ decision-making behaviour in energy-efficient retrofitting of office buildings.	China	Quantitative (tripartite evolutionary game model)	Stakeholders’ decisions in energy-efficient retrofitting of office buildings are heavily influenced by mutual benefits and costs. Government policies are effective when retrofit projects are profitable and public willingness is high.
33	Yang et al. [28]	Journal article	To analyse stakeholders’ behaviours in green retrofitting of traditional residential buildings.	China	Quantitative (tripartite evolutionary game model)	Government regulations and subsidies significantly boost participation. However, without direct incentives, effective publicity, education, and technological advancements can achieve similar results. The willingness of enterprises to invest depends on residents’ perceived benefits and risks.

).

2.2.5. Collation, Summarisation, and Reporting of Results

The fifth stage of Arksey and O’Malley’s [61] scoping review process is the categorisation and systematic reporting of research results based on seven distinct themes: project-related, contract-related, stakeholder-related, team-related, financial-related, regulation-related, and material/technology-related CSFs. These themes were identified to reflect the diverse aspects of the residential BER found by previous research. The statistical methods used by earlier studies in analysing the CSFs were also examined and organised. This categorisation provides a clear framework for understanding the CSFs for residential BER and allows for a systematic comparison.

3. Results

3.1. Selection of Selected Studies

The PRISMA-ScR flowchart used in the selection of the selected articles from their identification to final inclusion is presented in Figure 1, which shows that a total of 138 studies were found in three databases (Scopus—32, Web of Science—11, Google Scholar—67) and a citation search (n = 28). After removing three duplicates, 93 more articles were excluded based on irrelevant titles and abstracts. The remaining 42 articles underwent a full-text review, after which nine were excluded because of irrelevant contexts, an inaccessible full text, and a language other than English. In total, 33 studies were selected for the review. Since this total aligns with the range of studies utilised in previous related reviews (e.g., Almomani et al. [71]: n = 41; Chung-Camargo et al. [72]: n = 20; Lakhiar et al. [16]: n = 61), it is deemed acceptable for a scoping review of the existing literature.

3.2. Bibliometric Analysis of Selected Studies

To answer the first research question, this subsection presents the analysis of the characteristics of the studies included in this review. The characteristics analysed include publication trends, publication types and names, the country or region of focus, and the research methods.

3.2.1. Publication Trends

As shown in Figure 2, the publication trend shows three distinct phases, including the pre-pandemic era (2019), the pandemic era (2020), and the post-pandemic era (2021–2023). Residential BER research began to take shape slowly, with only one publication each in 2005 and 2011, indicating the early development of the research area. Moreover, building energy efficiency gained traction after the introduction of the Energy Performance of Buildings Directive by the European Union in 2002 [73]. A notable surge to four articles in 2019 reflects the increasing global focus on building energy efficiency and strategies for climate change mitigation following the Paris Agreement’s implementation.

The significant drop to one article in 2020 corresponds with the beginning of the COVID-19 pandemic. This decrease can be linked to various pandemic-related issues: nationwide lockdowns that limited field research and data collection in the construction sector, decreased funding for non-COVID research as global research priorities shifted to pandemic-related subjects, and interruptions in academic activities [74,75].

After the pandemic, publications increased significantly to six articles each in 2021, 2022, and 2023. This indicates the resumption of postponed research projects and a growing interest in BER as part of various governments’ “green recovery” initiatives [76]. However, the decline to three articles in 2024 can be attributed to funding availability and the usual delays between conducting studies and their eventual publication.

3.2.2. Frequency of Citations

The number of citations for the included studies was sourced from Google Scholar and analysed accordingly. As shown in Figure 3, the 10 studies with the most citations were Jagarajan et al. [40] (n = 213), Hwang et al. [68] (n = 197), Krarti et al. [29] (n = 149), Howden-Chapman et al. [67] (n = 141), Pardo-Bosch et al. [32] (n = 104), Liang et al. [17] (n = 97), Liu et al. [26] (n = 78), He et al. [27] (n = 63), Ohene et al. [35] (n = 59), and Monna et al. [31] (n = 47). The majority of studies with the most citations were published no later than 2019, which reflects enough time for their visibility by authors who have cited them.

3.2.3. Selected Publications by Country and Region of Focus

This analysis provides insight into the progress of academic and industrial practices in different countries or regions. As shown in Figure 4, we employed an elementary counting method in identifying the countries or regions with the most relevant publications. Publications without a clear geographical attribution were indicated as “not specified” (See Table 3). The highest number of publications came from China (n = 13), followed by Germany (n = 2), Saudi Arabia (n = 2), the UK (n = 2), and Europe (n = 2). China’s domination can be linked to its massive existing building stock requiring energy efficiency improvements, strict new building energy codes, ambitious carbon reduction goals, and government subsidies for residential BER programmes. On the other hand, countries with the least publications include Cyprus, Denmark, Italy, New Zealand, Palestine, Singapore, Ghana, and other developing economies, each of which has one publication.

Additionally, three articles did not identify the specific country or region of focus. To significantly reduce the global energy consumption and greenhouse gas emissions, researchers have highlighted the potential of residential BER. However, there remains a significant gap regarding implementation rates, technical expertise, financial support mechanisms, and policy frameworks supporting residential BER in different countries.

Figure 5 also shows the focus of the publications according to the regions of focus. This geographical distribution reflects how regions adapt their research focus to address local climatic conditions, economic circumstances, and social priorities while contributing to the broader global knowledge base in residential BER. The research landscape in residential BER reveals clear regional patterns and priorities. In the Asia Pacific region, China stands out as a major contributor, emphasising stakeholder engagement and behaviour, CSFs identification and governance, climate-specific solutions, and technical standards like EnerPHit. Other notable contributions from this region include Singapore’s research on green construction and New Zealand’s studies on the health impacts of BER.

Residential BER research in Europe exhibits a variety of country-specific interests. For example, research from Germany focused on market incentives and improving building energy efficiency, while the UK is exploring social housing and applications of AI. In the same vein, research was more focused on tools for maintenance planning in Italy, and preserving historic buildings is the area of focus in Denmark. In the Middle East and Africa, research directions vary significantly. While developing frameworks for net-zero energy was the research focus in Saudi Arabia, researchers in Palestine were interested in energy simulation studies. Research interest in Ghana centred around net-zero solutions suitable for tropical climates, while heat pump system adoption as a retrofit tool was studied in Cyprus.

In the Americas, research from the US centres primarily on residential energy audits and neighbourhood-level optimisation approaches. Despite these regional variations, the global research community converges on four fundamental themes: technical solutions focusing on energy efficiency and optimisation, policy and standards development, stakeholder engagement emphasising participation and behaviour, and economic factors addressing cost-effectiveness and market considerations.

3.2.4. Publication Type and Names

As shown in Figure 6, the analysis of the types of publications selected for this review reveals that 30 of them were peer-reviewed journal articles (91%), one was a published thesis (3%), and two were conferences (6%). This result suggests that residential BER research has moved beyond preliminary research stages to more comprehensive and validated studies worthy of journal publication.

Further analysis reveals the distribution of the publications according to the journal or conference in which they were published. A total of 25 publication names were recorded. The first five journals (having the highest number of publications) are Sustainability (n = 4), Energy and Buildings (n = 3), Heliyon (n = 2), Energy Efficiency (n = 2), and Applied Energy (n = 2). These journals published 13 articles (39.4%), while the remaining 17 (51.5%) published one article each. The remaining three publications (9.1%) comprised a combination of two conference articles (“4th Central European Symposium on Building Physics”) and one thesis (“Architecture and the Built Environment”). These details are summarised and presented in Figure 7.

3.2.5. Research Methods Adopted

Quantitative methods (n = 21: 64%) were the most used research approach in the selected studies; this was followed by mixed methods (n = 7: 21%) and qualitative methods (n = 5: 15%). This predominance of quantitative methods reflects the technical nature of the field of study, where researchers primarily focus on measurable variables. Mixed methods research combined technical assessments with stakeholder surveys and interviews, providing insights into the CSFs for residential BER. The relatively low proportion of purely qualitative studies suggests that while these CSFs have been approached quantitatively, the qualitative approach creates a robust explanation of the factors (see Figure 8).

3.2.6. Co-Authorship

This analysis investigates the extent of collaboration amongst researchers in a field of study. With a minimum publication threshold of 1, the total strength of the co-authorship link amongst 129 authors was analysed. Within a single cluster, 12 of these authors have the largest sets of collaborations (see Scheme 1). This result shows a low collaboration level amongst authors in the field of residential BER. Collaboration is important to enhancing the quantity of research in this direction and guaranteeing research quality and impact.

3.2.7. Authors’ Keywords Co-Occurrence

An analysis to ascertain the co-occurrence of keywords revealed a total of 137 keywords, but 11 of these met the threshold of 2. The largest node, as shown in Scheme 2 belongs to “energy efficiency” with eight occurrences, followed by “retrofitting” and “stakeholders” (three occurrences); “energy conservation”, “review”, “building retrofitting”, “energy performance certificates”, “social housing”, “economic viability”, “green retrofitting”, and “thermal comfort”, each had two occurrences. These keywords present the hotspots in the residential BER research with energy efficiency being the most focused on. With a threshold of two occurrences, 10 out of 11 keywords are connected. These were categorised into five clusters of keywords (see

Table 4. Cluster of keywords.

Clusters	Connected Keywords
1	Energy performance certificate, economic viability
2	Energy conservation, energy efficiency
3	Green retrofitting, review
4	Retrofitting, social housing
5	Building retrofitting, thermal comfort

and Scheme 2).

As shown in Scheme 2, the connecting lines indicate the number of studies in which two keywords co-occurred. The thicker these connecting lines, the stronger the link. Also, the size of the nodes and their labels indicate each keyword’s frequency of occurrence and suggest its level of importance. Furthermore, the distance between two keyword nodes reflects the strength of their relationship. In other words, two close keyword nodes indicate a more frequent co-occurrence [78]. The colour of the nodes also explains the cluster to which each keyword belongs.

3.3. Themes of CSFs

In this subsection, an attempt was made to answer the second and third research questions. Seven themes of CSFs (project-related, contract-related, stakeholder-related, team-related, financial-related, regulation-related, and material/technology-related), the data analysis method used in analysing the CSFs, and the research gaps are discussed as follows.

3.3.1. Project-Related Factors

Conducting comprehensive energy audits is a crucial first step in assessing energy consumption and identifying opportunities for energy savings and potential BER measures [39]. Energy audits provide the data to inform project planning and decision making, ensuring targeted and effective retrofit efforts [31].

Effective planning and management are foundational to the success of BER projects. Sang and Yao [18] highlight that a systematic approach to planning helps mitigate risks and set clear project objectives. Mejjaouli [34] emphasises the importance of a structured plan to ensure all BER aspects are thoroughly addressed. Additionally, detailed scheduling helps to optimise resource utilisation and minimise delays, especially without specific cost values [35,68].

Another critical project-related factor for the success of residential BER is the selection of blueprints and designs tailored to a building’s specific needs and constraints. Building and site-specific factors such as the geographic location, building type, size, age, local climate, orientation, and previous energy use significantly impact energy savings, making tailored audits essential for selecting effective BER measures [39,40]. Designing buildings with natural ventilation and lighting is frequently mentioned because they significantly enhance energy efficiency [30].

3.3.2. Contract-Related Factors

Contract-related factors are a major factor because the complexity of BER often necessitates detailed agreements to manage risks associated with construction disruptions and potential changes in the project scope. Clear contractual agreements help mitigate misunderstandings and conflicts during BER and reduce the associated barriers, particularly in social housing contexts where stakeholders’ engagement is essential [14]. Madushika and Lu [41] note that well-structured contracts can facilitate smoother project execution by outlining performance metrics and compliance with sustainability standards. Furthermore, contracts should incorporate clauses that address potential changes in the project scope due to unforeseen circumstances, which are common in BER projects [40].

3.3.3. Stakeholder-Related Factors

The successful implementation of residential BER requires the involvement of different stakeholders. However, stakeholders are more likely to emphasise factors that align with their interests and priorities, thereby leading to bias in their identification of CSFs [17]. For example, Yang et al. [28] revealed that the decisions of stakeholders, such as residents, government, and retrofitting enterprises, are influenced by their perceptions of benefits and risks. Therefore, raising awareness and educating stakeholders about the benefits and risks of BER is critical for increasing participation [17]. According to Huang et al. [25], homeowners are more likely to invest in BER if they have a clear understanding of its potential benefits and available financial mechanisms.

Active participation from stakeholders is essential for the effective management of BER projects, as it ensures that all perspectives are considered and that the project aligns with the interests of those affected [20]. Engaging stakeholders early on increases their enthusiasm for participating in BER initiatives, enhancing the likelihood of project success by considering their diverse perspectives and needs in planning and execution [70]. In particular, the commitment of building owners to energy efficiency has a direct influence on BER success [32].

Amongst the important stakeholders, engaging the community plays a critical role in BER implementation. A comprehensive framework that includes stakeholder participation in decision making can help address diverse homeowner needs and ensure BER programmes are effectively tailored to local contexts [34]. Howden-Chapman et al. [67] emphasise that effective community involvement and valued intervention by the participants are important factors for the success of retrofit action. Also, Liu et al. [26] demonstrate how different levels of public participation—before, during, and after retrofitting—impact energy savings by comparing three Beijing neighbourhoods with different BER models: a central government-led model, a local government-led model, and an old neighbourhood retrofit model.

Effective communication is fundamental for enhancing stakeholders’ trust and facilitating smoother retrofit project execution. The clear communication of sustainability goals can enhance stakeholders’ engagement and commitment to energy-efficient practices [17]. Furthermore, communication efforts, coupled with educational initiatives, foster collaboration and encourage input from various stakeholders, leading to innovative solutions and stronger project buy-in [42]. This is particularly important for enhancing homeowner participation in energy retrofit projects [25]. By addressing the motivations and concerns of stakeholders, communication helps build a sense of ownership and commitment, and ultimately a more successful energy-saving retrofitting [41].

3.3.4. Team-Related Factors

The expertise and technical knowledge of the project team play a critical role in the success of BER. A multidisciplinary team, including architects, engineers, and sustainability experts, is crucial for providing comprehensive insights into energy audits, conservation measures, and financing strategies for BER projects [40]. Collaborative governance and team dynamics are critical for enhancing problem-solving capabilities and fostering innovation, ultimately determining the success of BER projects and promoting sustainable development [41]. Jagarajan et al. [40] and Shen et al. [20] explain that continuous training, knowledge sharing, and the improvement of human resources, including professional knowledge, skills, and the selection of appropriate machinery and materials, are essential for overcoming BER challenges.

3.3.5. Financial-Related Factors

Financial-related factors are critical in the feasibility and adoption of BER. Cost concerns are a major hurdle for green building initiatives due to significant initial investments. However, providing financial incentives such as grants, tax credits, and subsidies can encourage homeowners to undertake BER, particularly where high upfront costs might be prohibitive [40]. The availability of financial mechanisms—such as grants, tax credits, low-interest loans, and subsidies—can reduce retrofit costs, making them more attractive to property owners, while integrating financial strategies into planning policies is essential for facilitating residential BER [6,24]. From the government’s perspective, the number of subsidies provided to residents can influence strategic decisions. However, if regulation and subsidies become too excessive, they may diminish the advantages for the government, leading it to adopt a “no incentive” approach [28].

Beyond initial investments, operational and maintenance costs are significant considerations in the decision-making process for residential BER. Cost is a crucial factor, and several strategies have been suggested to improve energy efficiency without placing excessive financial strain on building owners or occupants [17].

The prospect of increased rent from retrofitted residential buildings is a motivating factor for property owners. Groh et al. [23] concluded that energy-efficient buildings in the German rental market can command higher rents.

Ensuring the economic viability of BER projects through a thorough cost–benefit analysis and financial planning, including accurate cost estimation and payback periods, is crucial. This can help stakeholders understand the long-term savings associated with energy-efficient upgrades, thereby justifying the upfront costs [40]. Mejjaouli [34] develops a framework highlighting the required steps to plan and implement successful residential and commercial building retrofitting: data collection, life-cycle cost calculation, building simulation, and multi-criteria decision making (MCDM). The study found that retrofitting the case study buildings had a 2.2-year payback period.

The distribution of profits amongst stakeholders, including property owners, tenants, and investors, can influence the attractiveness of BER projects. While tenants enjoy energy savings, property owners often struggle to recover their investments through rental premiums [22]. This dynamic necessitates the careful consideration of market conditions and policy interventions to ensure that all parties are incentivised to participate in energy efficiency initiatives.

3.3.6. Regulation-Related Factors

Government policies and regulations play a significant role in facilitating the implementation of BER [6]. Government involvement is essential for implementing successful large-scale BER projects, particularly in residential buildings, as it provides the necessary guidance and encouragement for homeowners [29,37]. Given that BER does not often completely compensate for the incurred costs, Galvin [22] suggests specific policy interventions to compensate for market anomalies.

Regulatory frameworks often dictate the minimum energy performance standards that must be met, and failure to comply can result in penalties or project delays [32]. Understanding and integrating regulations into the project planning phase not only streamlines the BER process by ensuring compliance with current laws, but also enhances the likelihood of project approval and support from governmental bodies [20,41]. Moreover, aligning project goals with regulatory objectives enhances the likelihood of project approval and support from governmental bodies [20]. Adhering to local and international energy efficiency standards ensures that BER meets the required performance levels [36].

3.3.7. Material/Technology-Related Factors

Technical aspects of BER are essential for achieving energy efficiency. The research indicates that utilising innovative technologies such as BIM can significantly enhance the project coordination and efficiency, thereby reducing delays and cost overruns [21]. Similarly, installing sustainable building materials, such as advanced insulation and renewable energy technologies, can significantly enhance the energy performance of retrofitted buildings [19,69]. The integration of explainable AI in assessing BER practices can provide valuable insights into the effectiveness of different technologies and materials, helping stakeholders make informed decisions [38]. Furthermore, adopting energy-saving technologies must be accompanied by adequate training and support for contractors and homeowners to ensure proper implementation [15].

This review reveals that, although seven themes of 26 CSFs for residential BER have been identified, four themes comprising stakeholder-related, project-related, regulation-related, and financial-related CSFs are the most frequently reported (see

Table 5. CSFs for residential BER.

Factor	CSFs Identified	Sources
Project-Related Factors	Conducting comprehensive energy audits.	[31,39]
	Effective planning and management.	[18,34]
	Extensive pre-project planning and detailed scheduling.	[35,68]
	Site and building characteristics.	[39,40]
	Tailored design considerations.	[30]
Contract-Related Factors	Clear contractual agreements.	[14,40,41]
Stakeholder-Related Factors	Stakeholders’ active participation and collaboration.	[20,70]
	Building owners’ commitment to energy efficiency.	[32]
	Effective community involvement in BER projects.	[34,67]
	Public participation at different stages (before, during, and after retrofitting).	[26]
	Effective communication amongst stakeholders.	[17,41,42]
	Awareness-raising and educational initiatives for stakeholders.	[25,27,28]
Team-Related Factors	Expertise and technical knowledge within a multidisciplinary project team.	[40]
	Collaborative governance and team dynamics.	[41]
	Continuous training and improvement in knowledge, skills, and human resources.	[20,40]
Financial-Related Factors	Financial incentives.	[24,28,40]
	Cost–benefit analysis.	[40]
	Financial viability through rent increase potential and reduced operational and maintenance costs.	[23,34,66]
	Profit-sharing considerations amongst stakeholders.	[22]
Regulation-Related Factors	Supportive government policies and incentives.	[6,29,37]
	Regulatory frameworks that set minimum energy performance standards for BER.	[22,33,41]
	Alignment of project goals with regulatory objectives.	[20,36]
Material/Technology-Related Factors	Use of sustainable materials such as improved insulation and renewable energy technologies.	[19,69]
	Implementation of BIM for efficient project coordination and cost control.	[21]
	Utilisation of AI for effective technology selection and assessment of BER practices.	[38]
	Training and support for contractors and homeowners.	[15]

). Also, less attention has been paid to investigating context-specific retrofitting solutions that consider regional differences, varying climatic conditions, and diverse types of residential buildings.

The adaptability of the CSFs for residential BER reveals a multifaceted and contextually nuanced landscape of implementation strategies. Project-related factors tend to be relevant across various regions. For example, comprehensive energy audits serve as a foundational approach, with research highlighting the need for tailored assessments that consider the specific residential buildings’ characteristics in different climates. While the fundamental principle of clear contractual frameworks remains consistent, certain mechanisms must be carefully adapted to local regulatory and market conditions, especially in social housing scenarios. This underscores the importance of detailed agreements that can address construction disruptions and potential changes in scope.

The strategies for engaging stakeholders need to be deeply embedded in local cultural and economic contexts. The core principles of raising awareness, educating participants, and ensuring active involvement are universal [25,28], but their execution requires significant localisation as community engagement, communication strategies, and motivation techniques can vary greatly across different regions and socio-economic settings [78]. Given the complexity of BER, MCDM frameworks offer a sophisticated approach to holistically addressing multifaceted challenges. By systematically integrating thermal comfort, the life-cycle assessment, and affordability, these frameworks provide a comprehensive methodology beyond traditional single-dimensional analyses, enabling more nuanced and context-sensitive decision making.

Furthermore, while Galvin [22] addressed policy interventions and regulatory challenges, the creation of tailored retrofit policies for specific residential types has not been thoroughly explored. This demands a thoughtful approach and requires a thorough examination of the distinct features of various residential types, recognising their energy requirements, structural limitations, and socio-economic backgrounds. Residential BER policies can vary greatly from one region to another. The involvement of governmental bodies in guiding, promoting, and potentially mandating energy retrofits is crucial. However, the specific regulatory frameworks need to be carefully customised to fit local economic and political contexts, where locally compatible energy-efficient retrofits are easier to identify [78].

Financial analyses by Groh et al. [23], Liu et al. [26], and Mejjaouli [34] have studied different economic mechanisms with obstacles ranging from high upfront investment costs to intricate profit-sharing models. However, more in-depth research is necessary to develop cost-effective retrofitting strategies beyond simple financial assessments. This demands a comprehensive approach that weighs the upfront costs against long-term energy savings, considers the economic limitations of the community, and utilises innovative financing options to ensure that sustainable improvements are financially feasible for affordable housing. While financial incentives such as grants, tax credits, and subsidies are widely acknowledged as essential, their application varies significantly depending on local economic conditions, government support, and market dynamics.

The technological aspect, studied by Armijo et al. [21], requires further investigation into how innovative technologies such as BIM and advanced materials can improve energy efficiency and climate resilience. This means creating innovative solutions that not only lower energy use, but also improve buildings’ resilience to changing climate conditions, thereby ensuring infrastructure that is both sustainable and adaptable. However, the success of these initiatives relies heavily on local technological infrastructure, professional training, and economic viability. The need for collaborative governance and knowledge sharing crosses regional boundaries, although the availability of skilled professionals and resources can differ significantly. Therefore, continuous training and human resource development are critical, particularly in rapidly changing technological landscapes.

Ultimately, past studies have yet to sufficiently examine the complex interdependencies amongst these factors; thus, the development of a conceptual framework is suggested for further studies (see the next section).

3.4. Conceptual Framework of CSFs for Residential BER Implementation

As shown in Scheme 3, a conceptual framework was developed to show the interconnectedness amongst the seven themes of CSFs for residential BER implementation. This was motivated by a structured approach to managing the complexities of residential BER. The framework is structured to reflect two layers of influence: external and internal CSFs. The external layer consists of regulatory factors that largely influence the other elements within the internal layers. The regulatory requirements act as both enablers and constraints to retrofit implementation, setting minimum standards while potentially offering incentives that influence the financial viability, stakeholder decisions, and other factors in the inner layer.

The internal layer consists of project-specific factors that directly impact implementation. Project-related factors directly inform material selection and the deployment of retrofit technologies. For example, an energy audit could reveal structural limitations that influence both material choices and the scope of BIM implementation. The project-related factors provide the technical foundation that supports and is supported by material and technology considerations. The framework also demonstrates how team-related and contract-related factors are intrinsically linked; team expertise influences contract formulation, while contract terms can affect team composition and performance.

At the core of both layers, stakeholder factors act as a crucial bridge between external and internal layers, highlighting how stakeholder interests and engagement levels can either accelerate or impede the success of residential BER. Financial factors permeate other factors in the framework and could act as enablers and constraints. All the factors in both layers ultimately converge towards the central objective of residential BER implementation. The framework is a valuable tool for stakeholders to ensure the comprehensive consideration of all CSFs for residential BER.

3.5. Methodologies for CSF Analysis

Of the 33 studies selected for this review, four focused directly on analysing the CSFs for residential BER [18,20,25,27]. The literature presents various statistical methods for analysing CSFs for residential BER. While these methods have their strengths, they also have limitations that may prevent them from fully capturing the complex and multi-dimensional aspects of residential BER.

Shen et al. [20] utilise the SNA method to investigate the interactions amongst stakeholders engaged in residential BER initiatives. The study started with a comprehensive literature review to identify potential CSFs and relevant stakeholders. This is followed by developing a conceptual framework that shows the interactions amongst stakeholders and the CSFs. Data were collected through surveys targeting various stakeholders, including homeowners, contractors, and government officials. The relationships between stakeholders and the identified CSFs were analysed using SNA techniques. The study highlighted that while SNA was effective for visualising network structures, it lacked depth in addressing the complex combinations of CSFs that vary by context [20,54].

Huang et al. [25] investigate the factors influencing homeowners’ willingness to invest in residential BER. This study employed a survey-based approach for data collection, and regression analysis was utilised to assess the significance of various factors, including financial incentives and the awareness of energy efficiency benefits. Sang and Yao [18] employ a mixed-methods strategy that integrates both qualitative and quantitative research methods to explore and assess the CSFs for enhancing energy efficiency in existing residential buildings across China. The research commenced with an extensive literature review to pinpoint potential CSFs, which were subsequently validated through interviews with experts engaged in residential retrofitting initiatives.

After the qualitative phase, Sang and Yao [18] developed a survey rooted in the CSFs they had identified. This survey was subsequently disseminated to a broader audience of industry experts, including architects, engineers, and project managers. The study employs statistical methods such as factor analysis and regression analysis to ascertain the significance and relationships amongst the identified CSFs. The regression analysis identifies and measures the impact of specific factors on the success outcome [53]. Meanwhile, factor analysis helps to identify a relatively small number of underlying unobserved factors that could explain certain interdependencies amongst a larger set of observed variables [79]. However, these methods assume a uniform significance across CSFs, often neglecting the diverse contexts and interdependencies that can impact residential BER differently, depending on local conditions, building types, and stakeholder priorities [18,53,78].

He et al. [27] examine the factors influencing residents’ intentions towards the green retrofitting of existing residential buildings. The study employs a survey-based approach to collect data from residents regarding their intentions to engage in green retrofitting. The authors used SEM to analyse the relationships between the factors influencing intentions, including policy support and perceived benefits. Although SEM provides insights into causal relationships amongst variables, it is constrained by a reliance on pre-defined models and linear associations, limiting its ability to handle the diversity of CSF interactions that influence retrofit outcomes [80].

The complexity, context-specificity, and dynamic nature of residential BER highlight the need for more suitable analytical techniques, such as fsQCA. FsQCA has garnered increasing interest lately due to its distinct advantages in merging qualitative insights with quantitative rigour. It calibrates data on a 0 to 1 scale, making it attractive to qualitative and quantitative researchers seeking precise interpretations [81]. In contrast to traditional variance-based approaches that concentrate on individual net effects, fsQCA investigates the interplay of conditions across various patterns and includes unique subsets of cases [57].

Moreover, fsQCA is adaptable to different sample sizes and data types, enabling researchers to work with both small samples (up to 50) and extensive datasets (in the thousands), while also allowing for the inclusion of categorical variables. This method uncovers configurations that elucidate a segment-specific sample, including cases other methods consider as outliers [57]. Although fsQCA demands a thorough understanding of the variables and context for effective calibration and analysis, this in-depth engagement significantly improves the quality of outcomes, merging qualitative and quantitative data for more comprehensive insights [82]. Consequently, utilising fsQCA enables researchers to uncover intricate interdependencies and configurations of CSFs, ultimately fostering the development of more effective residential BER strategies that align with sustainability goals.

Application of fsQCA

The seven themes of CSFs for BER projects cover a broad range of interconnected elements. By employing fsQCA, we can pinpoint the combinations of these elements that contribute to successful results. Many software applications, including fsQCA software, R packages (e.g., QCA and Set Methods), and TOSMANA can be used for this analysis. However, fsQCA 3.0 software is used in the following hypothetical example to demonstrate the steps to follow in using fsQCA.

• Step 1: Define the Outcome and Causal Conditions

The initial step in fsQCA is to define the outcome variable and the causal conditions. The outcome, in this case, is defined as successful residential BER implementation (Y), to achieve a 30–40% reduction in energy consumption [10]. The causal conditions consist of the seven CSF themes, but for simplicity in this example, we include one representative factor from each theme:

• Project-related: energy audits (X₁).
• Contract-related: clear contracts (X₂).
• Stakeholder-related: stakeholders’ collaboration (X₃).
• Team-related: technical expertise (X₄).
• Financial-related: financial incentives (X₅).
• Regulation-related: supportive government policies (X₆).
• Material/technology-related: sustainable materials and technologies (X₇).

• Step 2: Entering Data into Software

The raw data gathered through a 5-point Likert scale (1 = “Not Critical” and 5 = “Very Critical”) are stored in a CSV (comma delimited) file format. After storing the data, they can be opened in the software by clicking File >> Open. This returns the interface shown in Scheme 4.

• Step 3: Data Transformation and Calibration

Before calibrating the data, researchers need to calculate the construct scores by finding the minimum, maximum, and average of the data in each column (i.e., X₁ to X₇). This can be done manually or by using appropriate functions (=max (), =average (), and =min ()) in MS Excel^®, as shown in Scheme 5.

The next action is to calibrate the data into fuzzy-set scores ranging from 0 to 1 using the Variables >> Compute menu. The target variable is named by clicking the “calibrate (x, n1, n2, n3)” function, where “x” refers to the seven factors highlighted earlier, “n1” represents the threshold for full-membership, “n2” represents the cross-over point, and “n3” connotes the threshold of non-membership in the target set. Take X₁, for example, n1 is 5, n2 is 3.867, and n3 is 2. This is repeated for the remaining six factors. Following this process, the data transforms into the fuzzy sets accordingly (see Scheme 6). Calibrating these values returns an upper bound of 0.95 and a lower bound of 0.05 [83].

• Step 4: Construct the Truth Table

The truth table outlines all possible combinations of causal conditions and their respective outcomes. The truth table can be computed by selecting Analyse >> Truth Table Algorithm. To execute this algorithm, choose the Y (outcome or dependent variable) condition as a “Set” in the “Select Variables” menu, and then add the antecedent conditions X₁–X₇ (independent variables) accordingly. The results from the fuzzy set indicate the number of cases that reflect the combination of conditions (i.e., configuration). By conducting the standard analysis (encompassing all potential causal combinations), the consistency and coverage of these configurations are determined. With seven causal conditions, there are 2⁷ = 128 possible configurations. However, only those with a consistency of >0.8 and coverage of >0.2 can be deemed sufficient configurations to produce an outcome. This can be achieved by clicking the Edit >> “Delete and Code…” menu (see Scheme 7).

• Step 5: Solution Analysis and Interpretation

The results of fsQCA provide three types of sufficient configurations: complex, intermediate, and parsimonious [83]. The complex solution calculates the largest number of configurations, but because it is impossible to interpret all configurations of complex solutions, intermediate or parsimonious solutions are recommended [83]. According to Ragin [83], the parsimonious solution considers only the essential configurations, while an intermediate one stands between the complex solution and the parsimonious solution.

By clicking on Standard Analyses, the following is generated. Scheme 8 shows how the method allows researchers to state whether a condition must be present; otherwise, the default Present or Absent is set.

By clicking ok, the complex, intermediate, and parsimonious solutions are generated. However, because it offers a robust, theoretically informed, and empirically grounded pathway to understanding causal configurations, the intermediate solution is the gold standard for interpreting fsQCA results [83]. In this example, the intermediate solution presented in

Table 6. Sufficient configurations for CSFs.

Configurations	X1	X2	X3	X4	X5	X6	X7	Raw Coverage	Unique Coverage	Consistency
~x1 * x3 * x4 * x5 * ~ x6 * x7								0.341521	0.14503	0.9125
x1 * ~ x2 * x3 * x4 * ~ x5 * ~ x6 * ~ x7								0.181287	0.0467837	0.828877
~x1 * ~ x2 * ~ x3 * ~ x4 * x5 * x6 * x7								0.14269	0.0549709	1
x1 * x2 * ~ x3 * x4 * x5 * ~ x6 * x7								0.194152	0.0584797	1
x1 * x2 * x3 * x4 * x5 * x6 * x7								0.256141	0.141521	1

Solution coverage: 0.643276; solution consistency: 0.901639; frequency threshold = 1; consistency threshold = ≥0.8. Note. Asterisks (*) means “logical intersection”, tilde (~) indicates negation or absence of a condition, ‘o’ represents an intermediate solution pathway, shaded ‘o’ signifies a core solution pathway, and a blank cell suggests no relevance of that condition in the analysed pathway.

shows five configurations: configuration 1 indicates that X₁ and X₆ are not as critical as X₃ to X₅ and X₇. For configuration 2, X₁, X₃, and X₄ are more critical than X₂ and X₅ to X₇. The case is different for configuration 3, which suggests that X₅ to X₇ are more critical than X₁ to X₄. Configuration 4 indicates that X₁, X₂, X₄, X₅, and X₇ are more critical than X₃ and X₆. Lastly, configuration 5 recommends that all the conditions (i.e., X₁ to X₇) are critical. With a consistency of >0.8 and raw coverage of >0.2, configurations 1 and 5 are sufficient causal combinations of conditions for the CSFs for residential BER implementation [83].

However, necessary conditions are checked by clicking the Analyse >> Necessity Conditions menu. This action pops up a dialogue menu comprising positive and negative “~” conditions (calibrated data), either of which can be used consistently. The conditions (X₁ to X₇) are transferred to the conditions box while the outcome (y) is transferred to the outcome box on the right side, all using the “→” bottom. Given that none of the conditions were consistent in all five configurations, the consistency values, as shown in Scheme 9, are <0.9. This means that none of the conditions tested are necessary conditions for residential BER implementation.

4. Implications

This review underscores the importance of seven CSF themes (project-related CSFs, contract-related CSFs, stakeholder-related CSFs, team-related CSFs, financial-related CSFs, regulation-related CSFs, and material/technology-related CSFs). These results have several implications for policymaking and research.

4.1. Policy

Developing policies that focus on energy audits could significantly improve the effectiveness of residential BER, allowing property owners to gain a clearer understanding of their energy consumption and pinpoint suitable retrofit solutions. Energy audits should be customised to fit local climate conditions—focusing on minimising heat loss in colder areas, managing solar radiation in dry regions, and controlling moisture in humid climates. The goal is not only to assess, but also to provide actionable insights that inform specific retrofit strategies.

The regulatory framework surrounding residential BER is crucial, as it underscores the necessity for substantial government backing to streamline the approval process and establish minimum energy performance benchmarks, ultimately promoting a wider adoption of retrofit initiatives. In Nordic countries, for instance, regulations may focus on strict insulation standards and technologies for heat retention, whereas Mediterranean policies might prioritise integrating solar energy and cooling efficiency. Developing nations often need more adaptable strategies that align energy efficiency objectives with wider economic development requirements.

Equitable contractual and team management practices are essential in residential BER projects. Adaptable contractual frameworks highlight the potential benefits of policies that establish clear performance metrics, sustainability standards, and collaboration protocols that can adapt to various economic situations. Achieving this necessitates a careful balance between offering a structure and allowing for flexibility, especially in social housing. Fair contracts include specific performance metrics, risk-sharing, and fair compensation mechanisms to safeguard service providers and property owners. Contracts should also feature clauses that address potential technological uncertainties, allow necessary adjustments, and outline a clear dispute resolution process. In diverse socio-economic settings, contracts should be adaptable enough to reflect local differences while upholding essential standards of professional conduct and project execution. This strategy fosters trust and reduces the likelihood of conflicts among stakeholders.

Teams engaged in these initiatives should be organised to foster interdisciplinary collaboration, ensuring that technical experts, policymakers, financial analysts, and community representatives work together effectively. This involves defining clear roles, establishing transparent communication channels, and implementing performance evaluation systems that encourage collective success over individual competition.

Moreover, the insights regarding stakeholders underscore the necessity of inclusive policies that foster their active participation. This resonates with prior studies that suggest that participatory methods can boost community support and foster sustained engagement in residential BER. Effective strategies must acknowledge significant cultural differences in decision making [78]. Indigenous communities require methods that genuinely honour traditional knowledge and local environmental insights.

While policies may focus on achieving community consensus, personal economic incentives take precedence. In other words, financial policies considering tax incentives, grants, subsidies, and innovative financing options like green bonds and microfinancing are essential to make residential BER more affordable and feasible for property owners burdened by significant upfront costs. These strategies should be tailored to the local economic conditions, as regions rich in resources will require different approaches unlike those with limited resources [78].

The integration of technology adds another layer of complexity. Policy frameworks should facilitate a technology transfer and innovation while acknowledging the significant disparities in technological infrastructure. Regions with advanced technology might prioritise cutting-edge solutions such as AI-driven energy management. However, developing areas may need simpler, low-tech solutions that are easier to implement and maintain.

The main challenge for policymakers is to establish a regulatory environment that is both structured and flexible. Achieving success will involve ongoing dialogue, interdisciplinary collaboration, and an understanding that energy retrofitting is not merely a technological issue, but a multifaceted social, economic, and environmental endeavour. This requires policymakers to go beyond generic recommendations and craft sophisticated, context-specific strategies that recognise the complex interplay between technological innovation, financial limitations, and environmental needs in residential BER.

4.2. Research

The findings from this extensive review underscore the urgent need for a more refined, interdisciplinary strategy to grasp the success of residential BER. The past literature has largely concentrated on isolated CSFs. However, the gaps identified in the research highlight the necessity for a more detailed investigative framework that can capture the intricate relationships amongst stakeholder perceptions, technological advancements, policy structures, and economic factors. Future research should particularly focus on developing MCDM models that can address thermal comfort, the life cycle assessment, and affordability simultaneously, while also considering regional differences and various residential types.

From a methodological perspective, this approach requires sophisticated analytical techniques to unravel the complex interdependencies amongst different CSFs [55,57]. Therefore, researchers should aim to develop configurational methodologies that investigate how combinations of factors—rather than single variables—lead to successful BER outcomes. This will necessitate innovative research designs that merge qualitative insights with quantitative analysis, potentially employing fsQCA to explore the conditional relationships amongst stakeholder engagement, technological integration, financial mechanisms, and regulatory support.

Additionally, the research implications advocate for a more context-sensitive approach that transcends generic retrofit strategies. Future studies should aim to create adaptive frameworks that can be customised for specific residential settings, considering unique elements such as local climate conditions, building types, and socio-economic factors. This would involve developing comprehensive research protocols that not only pinpoint effective retrofit strategies, but also offer flexible implementation guidelines that can be tailored to different contexts.

5. Conclusions

This review synthesised the previous literature on the CSFs for residential BER and how these factors are analysed. To achieve the research objectives, we adopted a scoping review methodology to synthesise previous studies on residential BER. The review adopted Arksey and O’Malley’s framework in the systematic search for relevant studies, the selection process, data extraction, and categorisation of identified CSFs.

We analysed the 33 selected studies’ characteristics, and the publication trends revealed three distinct phases: the pre-pandemic era saw a slow growth in residential BER research, the pandemic era experienced a decline, and the post-pandemic era saw a resurgence. The publications are predominantly peer-reviewed journal articles (91%), with the top journals being Sustainability, Energy and Buildings, Heliyon, Energy Efficiency, and Applied Energy. Geographically, China dominates the research, while other regions exhibit varying research foci based on local contexts. The analysis of the authors’ collaboration revealed the largest sets of collaboration amongst 12 authors, and 10 keywords related to “energy efficiency” emerged as the most frequently used. Methodologically, quantitative research methods were mostly adopted (63%); this was followed by mixed methods (22%) and qualitative methods (16%).

Twenty-six CSFs for residential BER were identified in the selected studies. We categorised these factors into seven themes (project-related, contract-related, stakeholder-related, team-related, financial-related, regulation-related, and material/technology-related CSFs). However, four CSFs were most frequently emphasised: stakeholder-related, project-related, regulation-related, and financial-related CSFs. This highlights the need for effective collaboration amongst stakeholders, strong regulatory support, and specific financial incentives to encourage the widespread implementation of retrofit initiatives. The results reveal the interconnected nature of CSFs, suggesting that isolated strategies fall short of addressing the challenges associated with residential BER. Furthermore, a significant methodological gap was noted, as only a few studies have utilised analytical approaches that effectively capture the conditional relationships between CSFs.

This review lays the groundwork for policymakers and practitioners by emphasising the necessity of a flexible, multifaceted retrofit approach that supports energy efficiency and sustainability goals. It also stresses the importance of continued research to comprehend effective configurations of CSFs, ultimately creating a conducive environment for strategic retrofit initiatives to flourish across diverse regional and socio-economic contexts.

While this review offers valuable insights, it is not without some limitations that call for caution in the application and generalisation of its results. The review primarily relies on the existing published literature, which may not capture all relevant but unpublished research, potentially affecting the conclusions’ completeness. Also, differences in the terminology, research focus, and methodologies amongst the studies reviewed created challenges in synthesising and categorising results, which might impact the accuracy of the identified themes. Furthermore, the review’s reliance on thematic categorisation lacks a comprehensive analysis of the inter-relations amongst CSFs. This oversight means that the intricate and evolving nature of the elements in the actual residential BER may not be adequately captured. Lastly, various regions possess unique residential BER requirements. However, considering the limited literature, we could not compare based on climate- or region-specific criteria. As a result, the identified CSFs may not accurately represent the peculiarities of different climates or regions.

Building on these identified limitations, future empirical studies should adopt a more comprehensive and nuanced approach to exploring the CSFs for residential BER. The research should explore the less studied themes, particularly technology-, team-, and contract-related CSFs, while also considering the wider context of sustainability regulations and innovative financing models. Given the complex and multifaceted nature of BER, researchers are advised to utilise advanced methodological approaches such as fsQCA to reveal the intricate configurations and interdependencies amongst CSFs in various contexts.

The research needs to go beyond traditional single-factor analyses by developing a comprehensive framework that illustrates how CSFs interact dynamically and differ across climatic zones and socio-economic settings, with a special focus on the unique challenges that developing economies encounter. This approach requires an interdisciplinary research strategy combining technological innovations, stakeholder perspectives, policy frameworks, and economic factors to achieve a well-rounded understanding of successful residential energy retrofitting. By employing such a detailed, context-sensitive methodology, researchers can offer more valuable insights that can be transformed into flexible strategies for executing energy retrofit projects in diverse environmental and socio-economic landscapes.