Due to greenhouse gas emissions, climate change has become a global challenge in recent decades [1]. As a response, Australia has committed to reducing its CO₂ output by 43 % of its 2005 levels by 2030, and then to net zero emissions by 2050 [2]. Aligning with this net zero commitment, Australia’s “Trajectory for Low Energy Buildings” set out the national plan for the residential building industry to achieve zero-energy and carbon-ready sector by 2030 [3]. In Australia, the minimum energy standards for new buildings are considered essential policy instruments for lowering energy consumption and carbon emissions from the built environment. The minimum performance standard before the 2022 update to the National Construction Code (NCC) was to achieve a Nationwide House Energy Rating Scheme (NatHERS¹) 6 stars for new housing. However, this minimum standard has increased from 6 to 7 stars under changes to the NCC 2022, which will become mandatory for the State of Victoria in Australia from May 2024. Many researchers have underlined that 6 or even 7 stars are not sufficient for Australia to achieve net zero emissions. An optimal economic and environmental energy standard should be beyond 7.5 stars [4]. Nevertheless, the latest NatHERS data from the HStar² dashboards reveal that 79.88 % of new Victorian housing between May and October 2023 (i.e., the transition period toward the 7-star standard) was designed only to achieve the minimum NatHERS 6-star standard, approximately 7.15 % went 7 stars and beyond, and only around 1.18 % went beyond the optimal 7.5 stars [5]. This lower rate of beyond-compliance design is perhaps expected, given that many of these homes were already in the design or planning stages and thus not required to anticipate the 7-star threshold. Nevertheless, with the 7-star minimum becoming mandatory and the long-term industrial transition toward net zero emissions objectives, limiting new housing to minimum standards may fall short in addressing these goals. Given the gradual pace of regulatory changes, a critical challenge is to foster industry practices that encourage beyond-compliance outcomes. Going beyond minimal compliance will drive substantial progress toward net zero emissions targets, making it an urgent challenge to tackle [6].

On a worldwide scale, similar challenge is observed – Several studies have demonstrated that the energy performance of new houses in many countries, including the US, the United Kingdom (UK), South Korea and Australia, is sub-optimal when considered from an environmental and economic perspective [4]. South Korea introduced its Building Energy Code in 2001, but by 2016, most residential buildings were designed to solely meet minimum standards. Among the 30,489 permits issued that year, just 0.05 % achieved the government-promoted zero-energy level [7]. In the UK, Gupta and Kotopouleas [8] reported that many new homes are also designed to fulfill merely the minimum energy performance standards, with few achieving beyond-compliance outcomes. The UK Committee on Climate Change (2019) has called for new homes to go beyond-compliance for a low-carbon, sustainable future [9]. In Illinois (US), homes must score 62 or lower on the Home Energy Rating System, with lower scores indicating higher energy efficiency. In 2022, the state’s average score was 58, just above the required minimum [10].

Among all the reasons for not exceeding minimal compliance, such as the frequently-researched inadequate transitional support from building authorities and low client demand for homes beyond code minimums, recent studies indicate that one of the arguments is the different behaviors of building practitioners in the compliance process, especially their willingness and ability to achieve beyond-compliance outcomes [11,12]. Since the NatHERS is calculated based on the simulation of the house design, the building practitioners who engage in the design phase of a project (e.g., architects, designers/draftspersons, builders, project managers and thermal performance assessors) are especially relevant. Building practitioners often serve as crucial intermediaries between policy expectations and client preferences. Their role involves executing the policies as well as advising and encouraging clients on the benefits of achieving beyond-compliance [13], which should in turn drive better beyond-compliance outcomes. Nevertheless, most academic works relating to building energy policies as well as sustainable buildings only focus on the top and bottom (i.e., policymakers and building consumers), while neglecting the middle actors’ (i.e., building practitioners’) willingness and capacity to achieve beyond-compliance with the energy policies [14]. This neglect wrongfully assumes that a zero-energy and low-carbon vision outlined in a policy is straightforwardly and instantly adopted by building practitioners without careful consideration [15]. As is further affirmed by Parag and Janda [16], building practitioners are critical middle actors who can upstream influence top actors like the policymakers, downstream influence bottom actors like the building consumers and also sideways influence the other building practitioners in delivering net zero building industry [17]. Their varying behaviors can lead to different beyond-compliance outcomes in the design stage. The key to achieve an overall beyond-compliance status in Australia is to understand these different behaviors so that building practitioners themselves can identify key areas for self-improvement, and policymakers can develop and execute tailored strategies to effectively motivate different building practitioners to go beyond-compliance. Notwithstanding this significance, no research effort has addressed the fundamental question: how to segment building practitioners based on behavior constructs. Therefore, to fill this research gap, this paper aims to explore the segments of building practitioners based on their beyond-compliance behavior constructs when they face the transition toward 7 stars in the NatHERS. To accomplish this, the researchers employed a questionnaire survey designed based on the beyond-compliance behavior assessment model established in their previous work [18]. This survey collected data on various behavioral constructs of building practitioners. The analysis used k-means cluster analysis to explore segments within the surveyed practitioners based on their constructs. By presenting the first clustering analysis in the context of beyond-compliance with energy performance standards, this study offers valuable insights for building practitioners to identify areas for self-improvements. In addition, the study allows policymakersto identify tailored interventions to stimulate more building practitioners to advance toward achieving beyond-compliance outcomes. With more of them exceeding the minimum standard, the industry’s transition to net zero emissions will be accelerated.

As seen in Table 1, the first predictive variable is attitudes, which is typically defined as an individual’s overall evaluation—positive or negative—toward a specific behavior [26]. To adapt to the current context of building practitioners’ beyond-compliance when using the NatHERS, the attitudes refer to an evaluative predisposition toward beyond-compliance as a function of its determinant personal consequences [29]. According to Brown and Loosemore [30], Australian building practitioners’ attitudes may stem from perceived benefits through e.g., getting more clients, or differentiating their projects through competitive advantage [30]. Similar arguments were found in China [31]. Alternatively, studies in Australia and the US found that the attitudes can also come from building practitioners’ assumption of increased compliance costs with high energy performance designs [25,32].

Subjective norms, which refers to the perceived pressure or motivation from those significant referents, i.e., how the regulated building practitioner feels they will be perceived by others [33]. Tam, et al. [34] and Enker and Morrison [12] stated that Australian building practitioners’ beyond-compliance behavior can be influenced by their expectations of industry peers or clients. Zapata-Lancaster and Tweed [15] concluded with similar arguments in the regulatory setting of UK’s building industry. Thus, this variable was operationalized to reflect the perceived social pressures from important referent groups such as clients, peers, and other industry stakeholders.

Perceived behavioral control concerns an individual’s perception of their ability to perform a behavior, determined by their confidence in their knowledge and skills, the perceived ease or difficulty of the task, and external constraints. In this context, according to Cooper [29], it was operationalized to a building practitioner’s understanding of their capacity to achieve beyond-compliance outcomes. A report commissioned by the Government of South Australia revealed that situational constraints (such as shortage of specific building materials) hinder building practitioners from achieving higher energy star ratings [35]. In the UK, knowledge and skills possessed by building practitioners to design a high energy star rating house are considered a relevant factor [36].

Personal norms are self-expectations to conduct or refrain from engaging in beyond-compliance [28]. They arise either from internalized moral agreement with the policy objective or from the content of the policy itself [37]. Research in Australia and UK found that beyond-compliance behavior is dependent on building practitioners’ moral agreement with substantive goals in the building energy policy, or on the agreement level with the policy content [28,38].

Behavioral intention is a critical determinant of behavior, referring to the motivational factors that influence a person’s decision to perform a specific action [26]. In this model’s context, the intention to achieve beyond-compliance is measured by the willingness and efforts devoted to executing beyond-compliance outcomes. It reflects a building practitioner’s deliberate choice and commitment to exceed the minimal regulatory standards.

Actual beyond-compliance refers to the observed frequency or outcomes of beyond-compliance actions in practice. In this context, following Gram-Hanssen and Georg [39], the operationalization based on the previous frequency of delivering beyond-compliance projects implies the actual beyond-compliance outcomes.

Notwithstanding the identification of these interrelated predictive variables shaping the behavioral intention and actual beyond-compliance outcome, previous studies did not differentiate building practitioners’ discrete beyond-compliance behavior in the context of achieving beyond-compliance when using NatHERS [12]. In the other regulatory compliance studies [28,40], investigating and clustering of the regulatees’ beyond-compliance behavior were shown to have implications for the regulators to design various interventions for each distinct group. In this way, the policy objective was achieved more efficiently. Therefore, to meet the residential building industry’s net zero emissions vision, it is important to explore the segments of the building practitioners based on their beyond-compliance behavior predictive variables regarding the NatHERS.

Based on the above-mentioned beyond-compliance behavior assessment model [18], a questionnaire survey was used for data collection. As previous behavior studies suggested, questionnaire survey can facilitate the retrieval of large dataset that first contains information about building practitioners’ different kind of variables that co-shape their beyond-compliance behaviors, and secondly, includes data with a broad variety of occupational characteristics [28]. In a similar vein, Li, et al. [41] used questionnaire survey to obtain data for examining building practitioners’ construction waste reduction behavior.

Following Fig. 1, the preliminary factor analysis was performed in the first instance. Most of the variables and indicators in the questionnaire showed their reliability and validity (see Appendix 1). There were only two exceptions. The factor loading of the indicator PBC3 “Perceived controllability in going 7 stars and higher” in the perceived behavioral control was 0.578, which was below the threshold of 0.7. According to Francis, et al. [55], the variable of perceived behavioral control must include two dimensions: controllability (PBC3) and self-efficacy (PBC 1 and PBC 2). Therefore, the researchers chose to accept PBC 3 despite its low loading index. A similar approach was used by Nielsen and Parker [28]. Another indicator PN5 “Agreement regarding whether going beyond 7 stars can lead to energy consumption reduction” for the variable personal norm had a factor loading of 0.699, which was below the cutoff of 0.7. Hair, et al. [56] argued that in exploratory research, a coefficient greater than 0.6 was also deemed acceptable. Hence, this item was kept. In addition to the assessment of reliability and validity, the Kaiser-Meyer-Olkin index was reported at 0.808, which suggested sample adequacy. Following the confirmation of the reliability, validity, and sample size adequacy, the main analysis was conducted and presented in the next sections.

In the cluster of lingerer, building practitioners exhibit the lowest attitudes, indicating a general disinterest in exceeding the minimum requirements. Their subjective norms and perceived behavioral control are also relatively low, suggesting that they neither feel significant pressure from external stakeholders nor are confident in their ability to deliver high-performance outcomes. This aligns with findings from studies in the UK where certain building practitioners similarly reported low interest or motivation to go beyond the minimum energy requirements due to perceived financial burdens [58].

Building practitioners in the cluster of close-followers express strong subjective and moral motivations to achieve beyond-compliance, as indicated by their high values of subjective norms, perceived behavioral control, and personal norms, but they fall short in action, with low attitudes scores holding them back. This suggests that while they recognise the importance of energy efficiency, especially in the context of environmental responsibility, they are constrained by perceived high costs or practical barriers. This behavior state is reflected in Swedish studies [59]. Although many Swedish building practitioners understand the benefits of low-energy buildings, economic constraints and client demand can act as significant barriers, preventing them from successfully delivering projects that go beyond the basic requirements.

Australian building practitioners in the cluster of leaders demonstrate high attitudes, subjective norms, perceived behavioral control and personal norms scores, indicating both strong motivation and confidence in their ability to deliver energy-efficient buildings. These practitioners recognise the business opportunities associated with high-performing projects and respond positively to both industry norms and client demand for sustainable, energy-efficient homes. This state mirrors findings from Amoruso, et al. [60] comparing the German and Norwegian situations. They found that the most successful building practitioners in achieving high energy efficiency tend to view beyond-compliance as a competitive advantage. They also found that practitioners who had successfully adopted energy-efficient practices often did so because of clear economic incentives and the ability to position themselves as market leaders. Additionally, in England and Wales, there is evidence of a small group of high performers who see the financial and reputational benefits of exceeding regulatory requirements, using energy efficiency as a unique selling point to attract clients [23]. As with the cluster of leaders in the current study, these practitioners often lead the market in delivering beyond-compliance projects.

Beyond this, the study also found that the difference between the three clusters was primarily shown as a big difference in the subjective norms. This implied that the client’s request for home design, or the desire to earn the acknowledgement of others were the main reasons that differentiated these 73 building practitioners in the decision-making of whether to go 7 stars or higher. According to the middle actor perspective introduced in Section 1, building practitioners possess an agency that extends beyond simply meeting client demands. This perspective offers deeper insights into the behavior and agency of building professionals. Recent findings by Simpson, et al. [61] highlight that building practitioners are eager to build their confidence through funded training, enabling them to more effectively recommend beyond-compliance solutions to clients. Such training not only increases their technical knowledge but also bolsters their confidence in advocating for beyond-compliance solutions to clients. In addition to training, building practitioners express an interest in incentives that recognise their role as an informal advisor to clients. For example, models like the gold-standard Construction Skills Certification Scheme in the UK could be adapted to recognise and reward their expertise. Practitioners have indicated that receiving commissions or similar rewards would encourage them to promote beyond-compliance practices to clients. These insights from Simpson, et al. [61] could be valuable for Australian policymakers seeking to empower building practitioners, enabling them to better influence clients toward adopting beyond-compliance house designs.

This study acknowledges several limitations. It relied on questionnaire survey instruments based on self-reported responses from building practitioners. Such limitations include concerns related to self-presentation, socially desirable responses, honesty, memory recall, and discrepancies between reported behaviors and actual practices. While these biases are inherent in self-reporting, efforts were made to mitigate their effects by ensuring absolute confidentiality and anonymity for survey respondents, following Dillman, et al. [62]. In addition, the study was solely conducted in the State of Victoria. A change of the behavior constructs’ values may alter the composition of the clustering solution and the generalizability of the results. Future research could be carried out in other Australian jurisdictions as well as in different countries, examining to what degree the clustering solution is affected by regulatory environments. In addition, future research should investigate how each behavioral variable influences beyond-compliance outcomes. By determining the extent of each variable’s influence, this research could offer concrete recommendations to policymakers regarding which variables to target and tailor in their initiatives.