4.1.1. Distribution across time:

The allocation of research articles within one decade is shown in Fig. 3. The oldest relevant articles reviewed were in 2011, while the most recent articles were in 2020. Study topic articles increased from 2009 to 2017 and then began a decreasing trend. Most articles were published between 2016 and 2017 (22 articles—52% of total articles in 12 years). Research on the subject began to decrease in 2018 and may decline or stabilize at a low number of publications in the next decade. The general findings of the factors that influence stakeholders’ decisions to retrofit their buildings are similar across diverse regions and building types, as will be discussed in detail in a later section. Moreover, these studies can be used as guidelines in retrofitting decisions in various contexts.

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4.1.2. Distribution across main journals:

Table 1 presents the distribution of articles among scientific journals. Seventeen out of 42 publications are in the journals classified within the Energy subject area (Applied Energy, Energy and Buildings, Energy Policy, Energy Procedia, International Journal of Energy Sector Management, Renewable Energy, and Strategic Planning for Energy and the Environment). Sustainability and health-related journals (i.e., International Conference on Urban Regeneration and Sustainability, International Journal of Environmental Research and Public Health, Journal of Cleaner Production, Journal of Green Building, Smart and Sustainable Built Environment, and Sustainable Cities and Society) represent the next significant portion, with 12 (29%) articles, followed by journals on building, facilities, and construction (19%), engineering (10%), and survey (2%). The dominant journals of the analyzed articles are Energy and Buildings, Energy Policy, and Sustainable Cities and Society, each containing five research articles that were selected for this study. Importantly, this finding reveals that the topic is being addressed in considerably diverse research communities, although predominantly in journals specializing in the Energy subject area.

TABLE 1 Distribution across journals

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4.1.3. Distribution across geographical regions:

The articles were coded to denote whether the study area was located within a developed or developing economy, as classified by the United Nations (Nations, 2019). Countries with developed economy identified in the study included Australia, Denmark, Germany, Greece, Ireland, Italy, Spain, United Kingdom (UK), United States, and other European counties that were not named. Countries with developing economy included China, Egypt, Malaysia, Nigeria, Sri Lanka, Taiwan, and Vietnam. One study combined developed and developing countries in the study (Jin & Marjanovic-Halburd, 2018); thus, this article was counted in both categories. Thirty of the studies, (71%), focused on countries with developed economies. The remaining 12 studies (29%) were conducted in developing countries. Distribution of case study locations of the research articles by regions is shown in Fig. 4. The studies were located in various regions around the world, including the following: Australia, China, Denmark, Egypt, Germany, Greece, Ireland, Italy, Malaysia, Nigeria, Spain, Sri Lanka, Taiwan, UK, United States, Vietnam, and a mix of several European countries that were not named. The country hosting the majority of studies was the United States, which appeared in 14 out of 42 articles. China was next, with six articles, then Australia and the UK, each with four articles. Although most articles covered a single region, two articles conducted a multi-country case study to compare the findings among diverse regions, both based on the significant differences and similarities.

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Si and Marjanovic-Halburd (Jin & Marjanovic-Halburd, 2018) found differences in expert opinions about retrofit projects between the UK and China, given their distinctive national contexts. Their case study showed that UK experts emphasize the economic performance of green technology, while Chinese experts place significant importance on technical performance. Tozer (Tozer, 2020) conducted interviews with experts from Stockholm, London, and San Francisco based on their similarities, including their international leadership in carbon governance, leadership heterogeneity, and evidence of leadership in building decarbonization. That study investigated the political effectiveness of implementing decarbonization initiatives. Case studies conducted in multiple countries in Europe were similarly aimed at examining the effect of the identical policies implemented in the countries. Valero et al. (Valero et al., 2016) investigated common pan-European challenges in making refurbishment decisions and presented insights regarding a proposed decision-support tool for local administrations. Haase et al. (Haase et al., 2015) found similar features amid the practices of rehabilitation of European shopping centers. Thus, the study used three shopping centers in different European countries to define the common drivers of retrofitting European shopping centers.

4.1.4. Distribution across building types:

The distribution of articles across building types is shown in Fig. 5. The buildings used in these case studies can be categorized into eight types: education, health care, lodging, mercantile, office, mixed commercial, historic building, and public facilities. This study partly follows the definitions of building types determined by the Energy Information Administration (EIA) (EIA) to simplify the classification where possible but keeps some definitions of types of buildings found in the original articles to maintain the particular characteristics of the buildings when being evaluated for energy retrofits. Studies of mixed commercial buildings are identified in 18 articles. These studies either did not specify in detail about the use of facilities or used multiple building types in their research to obtain a consensus about factors affecting retrofit in commercial buildings. For example, Clancy et al. (Clancy et al., 2017) identified drivers and barriers of energy efficiency by conducting 750 interviews across a statistically representative sample of commercial businesses in Ireland, including retail, hotel, public houses and restaurants, offices, and warehouses and storage. The second most studied building types are offices (9 articles), followed by lodging (5 articles). The articles focusing on hotels focused on the significant energy consumption of this building type. Luxury hotels may spend up to 50% of their expenses on energy (SLEMA, 2009) and represent a savings potential of 20% (Karawita & Withanage, 2013). Buildings categorized as for education were discussed in three articles, including for public and private schools and higher education institutions. The collected data covered use of the buildings for academic or technical classroom instruction, administration buildings, dormitories, libraries, and teaching hospitals. Public facilities were identified in three articles: one argued that limited studies analyze the implementation of sustainable measures in public buildings (Abdallah et al., 2016), and two explored how fundamental differences in the public sector compared to the non-government sector can present unique challenges to energy-efficiency projects (Alam et al., 2019; Bertone et al., 2018). The historic building was discussed in two articles that represented growing interest in focusing energy-efficiency efforts on historic buildings and emphasizing the value of preserving the structural qualities and aesthetics while still seeking energy efficiency (Lidelöw et al., 2019). Last, a health care building type and mercantile building type were each only used in one article for a case study, indicating the lack of examination about perceptions of energy-efficiency retrofits in these building types. Mohammadpour et al. (Mohammadpour et al., 2017) focused on examining patient safety during energy-efficiency retrofits of healthcare facilities. Haase et al. [8] filled the gap of studies in the mercantile sector by understanding the energy efficiency and sustainability issues in shopping centers.

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4.1.5. Overview of research objectives, data collection approaches, and participant characteristics:

Table 2 summarizes reviewed articles, including the region, building type, objective, data collection, case study and sample size, and participant characteristics. Most of the selected papers had straightforward goals to identify drivers, barriers, and information requirements to implement energy-efficiency retrofits. Some articles used specific building types for a case study, such as shopping centers (Haase et al., 2015), hotels (Xu et al., 2012), and schools (Castleberry et al., 2016). In contrast, other studies focused on the decision factors at different retrofitting phases, such as during the initial intention phase (Liang et al., 2016) and actual project level executions (Fasna & Gunatilake, 2019). Factors influencing energy retrofit were also identified in articles that defined the retrofit challenges by focusing on the stakeholders’ characteristics. For example, retrofit decisions were examined based on the impact of ownership type, tenant demand, and market competitiveness (Kontokosta, 2016) and the interactive effect of participants’ experience, knowledge, and roles on sustainable building practices (Nguyen et al., 2017; Zuhaib et al., 2017). Another theme of the selected articles included studies that aimed to comprehensively assess the state-of-the-art methods, processes, and technologies of retrofitting. For example, Mohammadpour et al. (Mohammadpour et al., 2017) examined current retrofit practices in healthcare facilities focusing on patient safety. Other studies assessed the preferences on various energy reporting, data tracking, and labeling mechanisms available in the market (Christensen et al., 2018) and examined the retrofit decision process by investigating relationships among decision factors (Kim et al., 2019). The remaining articles aimed at evaluating existing buildings with green standards (e.g., (Komolafe et al., 2016; Yang et al., 2018)), proposed a new methodology for optimal retrofit (e.g., (Komolafe et al., 2016; Roberti et al., 2017)), and evaluated new energy-efficiency programs or decision-support tools (e.g., (Zheng et al., 2019)).

TABLE 2 Summary of articles examining factors influencing energy-efficiency retrofits in buildings

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Nineteen out of the 42 studies used qualitative methods for data collection, such as interviews, meetings, document review, panel discussions, site visits, focus group discussion, and workshops to assess participants’ perceptions. Fifteen articles used a mix of quantitative and qualitative methods. The rarest method used was the quantitative method via survey, which was identified in eight papers. The case study sizes ranged from focusing on a single building case study (Gultekin et al., 2014) to covering the extensive building portfolio of a real estate firm located in multiple cities (Kontokosta, 2016). The study with the most participants was Clancy et al.’s (Clancy et al., 2017), which was comprised of 750 phone interviews that statistically represented diverse commercial businesses in Ireland. Experts and practitioners who participated in the studies through interviews, focus groups, and surveys worked in the built environment and held extensive experience in building retrofit projects. Professions that were represented included owner representatives (e.g., executives, facility managers, project managers, engineers), contractor representatives (e.g., managers, energy specialists), and consultants (e.g., technical advisors, architects). In addition, some studies required participants to have a particular experience depending on its study objectives. For example, a retrofit investment study of a historic building required perceptions from experts with many years of experience in cultural heritage (Roberti et al., 2017). Another study desired engineering professional participants with knowledge about green building concepts and rating systems when proposing a new energy-efficiency rating system for existing buildings (AbdelAzim et al., 2017). A few studies also included academic researchers for a specific building type (e.g., (Xu et al., 2011)), government officials for public buildings and a regional case study (e.g., (Alam et al., 2019)), and occupants for a customer-centric type of building (e.g., (Haase et al., 2015)).

4.2.1. Key factors based on assessment criteria:

Based on the SLR of 42 selected articles, this study identified 30 key factors that influence the implementation of energy-efficiency retrofits. These factors can be grouped into seven decision criteria, each of which emerged in multiple articles: economic feasibility (EF; 32 articles), team process (TPro; 29 articles), technical practicality (TPra; 28 articles), institutional characteristic (IC; 27 articles), governmental policy (GP; 24 articles), occupant impact (OI; 24 articles), and environmental impact (EI; 17 articles). EF is considered most important and has a strong interrelationship with other criteria, meaning that a change in financial performance can affect the performance of other criteria. EI criterion is mentioned least as an influencer of retrofit decisions. Table 3 summarizes the total number of articles and the frequency of the assessment criteria being coded. The following sections discuss the primary factors under each assessment criteria that influence retrofit decisions.

TABLE 3 Summary of articles and codes on assessment criteria of building retrofit

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EF—life cycle cost. Factors related to EF were observed in 32 of 42 articles reviewed (76%) and included life cycle cost, funding mechanism, payback period, and profit distribution. The participants across the literature consistently indicated that energy-efficiency improvements were ultimately made based on financial decisions. The primary factor under this criterion is life cycle cost, covering 74 of 136 codes (54%). The coded statements from the reviewed articles indicated that life cycle cost was seen as a critical measure of success. The high upfront cost of technology installation (Castleberry et al., 2016; Haase et al., 2015; Zuhaib et al., 2017), uncertainty in improving building value and rent (Fasna & Gunatilake, 2019; Liang et al., 2016), and financial risks of savings overestimation (Bertone et al., 2018; Bruce et al., 2015) are some barriers related to life cycle cost that hinder retrofit implementation. Participants across the reviewed literature often noted that a retrofit project can be implemented if it can generate an economic return. A retrofit realization can be driven by pursuing affordable retrofitting cost (Tsai et al., 2017) by starting with more minor, simple, low to no-cost improvements (Christensen et al., 2018). Other retrofits requiring significant capital investment can then be considered when financial incentives become available and the affordable retrofit projects prove to be a cost benefit within a short payback period (Christensen et al., 2018). While financial incentives help encourage retrofits, barriers associated with split incentives among stakeholders are highlighted in the reviewed literature. For example, when the government department tenant does not receive enough incentive to retrofit when public buildings are leased, ad-hoc financing mechanisms such as environmental upgrade finance could help address the split-incentives issue [49]. Energy-efficiency investment that can provide attractive economic returns through reduced building energy bills for tenants and higher rents for building owners will drive more implementation of energy-efficiency retrofits (Kontokosta, 2016).

TPro—coordination and collaboration. Factors categorized under TPro were mentioned in 29 of 42 articles reviewed (69%) and included coordination and collaboration, expert skills, management leadership, and team training. The primary factor is coordination and collaboration, covering 54 of 127 codes (43%). Some barriers to retrofits discussed regarding coordination and collaboration include lack of quality management system (Hou et al., 2016); weak negotiation power (Liang et al., 2016); the reluctance of energy companies to share data (Valero et al., 2016); lack of trust and good relationships (Woodroof, 2011; Xu et al., 2011); potential high coordination cost (Liang et al., 2016); lack of involvement of experts, owners, and occupiers, which leads to conflicting opinions (Bertone et al., 2018; Zuhaib et al., 2017); an unsystematic way of making decisions [54]; and difficulties in establishing communication between parties (Fasna & Gunatilake, 2019). Improving the project organization process is a key success factor to effective coordination. Senior leadership should involve multidisciplinary stakeholders, including facility managers and engineers, throughout the process as the key decision-makers who directly interact with the day-to-day building operations and the occupants [35]. Recommendations from the reviewed articles suggest the need to perform project management under internationally recognized systems, communicate the program’s goals and progress across stakeholders through eco-charrette to formulate a shared vision and produce a preventive maintenance plan (Alam et al., 2019; Kim et al., 2017; Xu et al., 2011).

TPra—system compatibility. TPra factors were identified in 28 of 42 articles reviewed (67%) and included system compatibility, risk management, project integration, technology readiness, site accessibility, and procurement process. Under this criterion, the most cited factor was system compatibility, covering 43 of 124 codes (35%). The physical limits on the types of energy-efficiency technologies that can be installed (Ginks & Painter, 2017; Jimenez-Pulido et al., 2020; Kontokosta, 2016), lack of spare parts for older equipment that requires major disruptions (Curtis et al., 2017), and lack of availability of one-stop solutions (Zuhaib et al., 2017) were some of the main concerns discussed by participants across the studies. Constructability, ease of installation, and functionality of the retrofit technology are critical in fueling stakeholders’ confidence to invest in energy-efficiency improvement (Mosgaard et al., 2016; Strachan & Banfill, 2017; Tsai et al., 2017). Evaluating the existing building condition and its environment and improving the inspection processes (Jimenez-Pulido et al., 2020; Liang et al., 2015) should be an essential step to minimize system compatibility issues during retrofitting.

IC—internal value. Factors related to IC—including internal value, demand pressure, community engagement, and reputation—were observed in 27 of 42 articles reviewed (64%). Internal value is mentioned the most, covering 30 of 78 codes under IC (38%). It is well known that companies may not see reducing energy use as a top priority when investing capital. In fact, participants in some studies even perceived energy-efficiency retrofits as work that could harm the value of their organization or building. For example, historic building experts are concerned that retrofits are insensitive toward architectural and cultural aspects (Zuhaib et al., 2017). They could lead to a loss of historical material and might not maintain the building’s heritage value (Ginks & Painter, 2017; Jimenez-Pulido et al., 2020; Zuhaib et al., 2017). A case study in Australia showed that building code development such as fire safety and disability access prevented heritage-listed buildings from being renovated for reuse because they became significantly more expensive to retrofit (Bruce et al., 2015). In another study, Ginks and Painter found a regional variation: conservation professionals in Scotland had different perceptions about energy retrofits in historic buildings than conservation professionals throughout the rest of the UK (Ginks & Painter, 2017). Consequently, overcoming this gap in knowledge and beliefs should be a priority when considering potential added value for all stakeholders. For example, most companies in a U.S.-based study believed eco-labels and energy ratings add value to their real estate assets by attracting the market and identifying improved energy performance (Christensen et al., 2018). When retrofitting historic buildings, conservation professionals and heritage agencies are encouraged not to view energy-efficiency renovations as modernizing the facilities but rather as ensuring the buildings’ long-term survival (Ginks & Painter, 2017).

GP—government commitment. Factors related to the GP were identified in 24 of 42 articles reviewed (57%); they included government commitment, standards and regulations, information sharing, and political influence. Government commitment is the most crucial factor, with 31 of 74 codes identified from the article (42%). Barriers to retrofits cited in the literature included lack of energy code enforcement and efficiency (Andrews et al., 2016), lack of citizen education (Valero et al., 2016), delays in getting approval from the local authority (Fasna & Gunatilake, 2019), and lack of knowledge and support of high-level government officials responsible for introducing retrofit programs (Alam et al., 2019). That study [17] further expressed concerns that energy-efficiency retrofits are not a priority unless the state government mandates them. Ensuring that the mandated target is realistic and is followed by clear guidelines is necessary for a successful mandate. Further, the commitment to the energy-saving program should also start at the implementation phases (Woodroof, 2011).

OI—satisfaction and wellbeing. Factors related to OI—including satisfaction and wellbeing, health and safety, educational program, and energy-efficient behavior—were mentioned in 24 of 42 articles reviewed (57%). Satisfaction and wellbeing were discussed the most, with 21 of 56 codes identified (38%). Key barriers to retrofits that were cited include interrupting productivity and complaints from tenants (Curtis et al., 2017; Strachan & Banfill, 2017). One study in a hospital setting focused on understanding the impact on patients during the construction phase of retrofitting (Mohammadpour et al., 2017). Three case studies of healthcare facilities indicated various patient safety and wellbeing issues included noise, vibration, coordination, dust, and asbestos. The study suggested that considering input from the occupants as end-users during the design phase will improve current practices.

EI—eco-friendly installation. Factors included in EI, such as eco-friendly installation, carbon dioxide emissions, sustainable resources, and waste management, were observed in 17 of 42 articles reviewed (40%). The primary factor under this criterion, covering 28 of 63 codes identified (44%), is eco-friendly installation, which explores the feasibility of implementing various energy-efficiency improvement strategies with an environmental emphasis. Examples include eco-friendly refrigerants and fire suppression systems (AbdelAzim et al., 2017), use of reused building materials in the project (Nguyen et al., 2017), and use of materials with recycled content (Jin & Marjanovic-Halburd, 2018; Nguyen et al., 2017). An empirical study about sustainable building practices in Vietnam suggested the need to provide green building-related training to experienced practitioners to successfully implement various sustainable building applications in conventional buildings (Nguyen et al., 2017).

4.2.2. Key factors based on diverse regions and building types:

This section discusses the 30 factors mentioned in the selected articles that apply across different regions and building types.

Factors by regions. Table 4 shows factors influencing retrofit decisions that emerged in different regions. Seventeen regions around the world were used as case study locations within the selected literature. Three factors discussed in most regions included life cycle cost (14 regions), system compatibility (11 regions), and coordination and collaboration (10 regions). China, the United States, Australia, and the UK cover most of the 30 identified factors; 27 factors emerged in China and the United States, while 23 factors emerged in studies in Australia and the UK. Denmark and Egypt explored the least number of factors—only four factors each. This observation is in line with the number of articles that explored these regions. The studies are more concentrated in the United States and China, with 14 articles undertaken in the United States and six articles in China, resulting in 90% of the factors identified for each country. In contrast, Denmark and Egypt were only represented by one article each, limiting the representation of more diverse factors for these countries (13%).

TABLE 4 Factors influencing retrofit by region

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Although research articles are primarily from developed countries with higher per capita income than developing countries, both types of countries see EF criteria that focuses on life cycle cost and funding mechanisms as the most dominant considerations. However, some differences in concern exist between developed and developing economies. Studies featuring developing economies raised more concerns about TPra, IC, and GP (85%, 85%, and 69% of the articles) when considering retrofit projects than did developed economies (60%, 57%, and 50% of the articles). Fig. 6 summarizes the percentage of articles that mentioned each decision factor. In studies conducted in developing economies, TPra issues were emphasized for risk management, technology readiness, and system compatibility (54%, 38%, and 38%). In studies conducted in developed economies, the most discussed factor was system compatibility (43%), while risk management and technology readiness were only mentioned in 20% of the articles. Issues related to standards and regulation were more emphasized when considering retrofit projects in developing economies than in developed economies. This finding is consistent with Liang et al. (Liang et al., 2015), who found that government and policy factors are significantly important in energy-efficiency retrofits in China, unlike another study in Australia that indicated the limited role of the government in green building development (Yang & Zou, 2014). However, the impact of political influence in retrofit implementation was discussed in 3 of the 30 studies conducted in developed countries, yet it was not mentioned in any of the 13 studies conducted in developing countries.

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Factors by building types. Table 5 demonstrates how the factors influencing retrofit decisions are represented in eight building types identified in the reviewed articles. Like the representation by region, life cycle cost is the factor most discussed across diverse building types; it is mentioned for seven out of eight building types used in the literature. It is followed closely by expert skills, risk management, demand pressure, internal value, and satisfaction and wellbeing, which are equally identified in six building types. Research articles using mix commercial buildings represented the most identified factors (28 of 30 factors), followed by offices (25 factors) and education and lodging (23 factors each). Healthcare facilities covered only two of 30 factors, including satisfaction and wellbeing and health and safety. Only one article used a healthcare facility as the case study; thus, this finding does not imply that other factors were not considered by the owners and managers of healthcare buildings. Instead, additional studies that focus on this building may reveal a more comprehensive list of factors considered.

TABLE 5 Factors influencing retrofit by building type

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