Exploring the Integration of Passive Design Strategies in LEED-Certified Buildings: Insights from the Greek Construction Sector

Abstract

As the global demand for energy-efficient solutions grows increasingly urgent, passive design strategies emerge not only as a means to support the reduction in energy consumption but also as a pathway to minimizing building operational costs while enhancing thermal comfort and architectural attractiveness. On the other hand, the recognition and significance of building environmental certification schemes are steadily increasing worldwide. Within this context, this research investigates the extent to which passive bioclimatic principles are understood, applied, and incentivized in contemporary sustainable building practices in Greece—focusing in particular on their representation within the LEED certification credit structure. Drawing on a questionnaire survey completed by 89 experienced Greek construction professionals, the findings indicate a significant gap between the theoretical value attributed to passive design and its practical implementation. The respondents attribute this gap to two key factors within the Greek context: the lack of adequate education and awareness among key project stakeholders, and the considerable complexity associated with the collaborative frameworks required from the early design stages. Additionally, LEED appears to offer limited incentives for integrating passive design strategies. Instead, it tends to favor technological solutions and follows a standardized structure with minimal scope for regional customization. Enhancing LEED’s region-specific features to reward passive strategies proven effective in local contexts would be particularly expedient in reinforcing its role as a robust and impactful tool for promoting sustainability.

1. Introduction

In today’s volatile context marked by the urgent global challenge of climate change and the dramatic rise in energy costs, the significant energy demand of buildings remains a pressing issue, especially as their design and operation contribute substantially to global emissions. In this context, all stakeholders involved in the complex, multi-phase process of designing, constructing, and managing buildings must now also prioritize minimizing energy consumption.

Improving energy efficiency in the building design can be conducted through two main types of measures: active strategies and passive strategies. Active design involves taking advantage of mechanical or electrical appliances for reducing energy consumption in buildings [1], i.e., optimizing the heating, ventilation, and air conditioning (HVAC) systems, hot water production, lighting, and other building services. In contrast, the concept of passive design (PD) is rooted in the logic of building from the beginning of human history when no mechanical systems existed, and aims to utilize natural resources and the immediate climatic environment to create healthy and comfortable living conditions [2]. PD strategies hold significant potential for enhancing energy efficiency as heating, cooling, and lighting needs are met primarily through building form, orientation, and material choices. As a result, overall energy loads and respective costs can drop substantially, while thermal comfort and buildings can achieve a more resilient, cost-effective, and sustainable energy performance. Evidence from hot-dry climates indicates that optimum combinations of passive elements—such as glazing, thermal mass, and insulation—can lower indoor temperatures by nearly 10 °C during peak summer conditions and reduce energy consumption by up to 60%, demonstrating their crucial role in achieving net-zero energy building goals [3].

In recent years, interest in passive strategies has been reignited due to their low additional investment costs compared to the potential energy benefits they offer [4]. Adopting however PD principles requires design decisions that effectively incorporate—from the early conceptual stage—factors such as geometry, orientation, massing and spatial layout. If poorly determined, it is exceptionally difficult to amend those features in later phases—especially when attempting to incorporate natural lighting, passive heating, or cooling strategies retrospectively [5].

Further to the above, in the context of the global effort for CO₂ emissions’ significant reduction in the near future (e.g., European Green Deal, UN Sustainability Goals), the concept of ‘green’ or ‘sustainable’ building has emerged, and various certification schemes have also been developed worldwide. Sustainability certifications have become increasingly embedded in the building sector, particularly in large-scale developments involving prominent architectural firms, contractors, and developers [6]. Specifically, buildings are verified by independent organizations to ensure they meet certain environmental and social standards and particularly comply with specific energy efficiency standards. The most popular certification system is LEED (Leadership in Energy and Environmental Design), which started in the United States and has since been adopted worldwide [7]. Numerous studies conducted in the US reveal a consistent upward trend in LEED-certified projects, signaling a broader shift toward sustainability in the built environment. This growth reflects both the economic and environmental benefits associated with certification, while also highlighting the role of LEED in promoting the adoption of innovative technologies, sustainable materials, and optimized design practices aimed at reducing environmental impacts [6]. In many instances, governments have acknowledged the effectiveness of sustainability assessment tools in establishing sustainability standards by integrating them into legislation. A prominent example is the state of California, where, from 1 January 2024, all new buildings and major renovation projects exceeding 10,000 square feet (930 m²) undertaken by state agencies, must achieve at least LEED Gold certification [8]. Even prior to this legislation, California had demonstrated a strong commitment to LEED-certified projects; in 2015, 12% of the state-owned building portfolio was already LEED certified [9].

In the process though of producing “green” buildings, PD strategies are often overlooked, even when their benefits are well proven [10]. A striking example is the “trend” of dark-colored newly built apartment buildings that have flooded Greek cities such as Athens, ignoring one of the basic PD measures for areas with frequent high temperatures: the use of light-colored surfaces. Similarly, the extensive use of large glass surfaces in commercial buildings significantly increases the energy needs of buildings to maintain internal temperatures at consistently acceptable levels via heating and cooling. All in all, although many architects understand the importance of PD, its practical application is highly inadequate [11], a trend that also seems evident in Greece.

The aim of this study is to investigate how PD strategies are perceived and applied by Greek construction professionals, and to explore their interaction with the LEED certification framework. This dual focus responds to a documented gap in the literature regarding empirical insights from the Greek context—a Mediterranean climate with high potential for passive approaches, thanks to its abundant solar radiation, mild winters, hot summers and appropriate wind patterns. As LEED adoption grows nationally, examining the extent to which it acknowledges and supports such strategies becomes increasingly relevant for shaping sustainable design practices in Greece.

The remainder of the paper is structured as follows: Section 2 provides a literature overview, organized into four subsections covering (i) PD strategies and their implementation, (ii) the LEED certification system, (iii) the interaction between LEED and passive strategies, and (iv) relevant literature specific to Greece. Section 3 outlines the research methodology, followed by Section 4, which presents the survey results. Section 5 offers a comprehensive discussion of the findings and recommendations, and finally, Section 6 concludes the paper with key insights and suggestions for future research.

2. Literature Review

2.1. PD Strategies and Their Implementation

Passive systems are often viewed as highly favorable solutions due to their minimal operational energy requirements and typically lower initial investment costs compared to active technologies. According to Lechner (2009), when a building is designed to address heating, cooling, and lighting needs primarily through passive strategies, mechanical and electrical loads can be reduced by up to 80%. Furthermore, this remaining 20% can be minimized even further when architects collaborate closely with engineers to integrate efficient systems into the overall design [12]. Hu et al. (2023) found they can cut cooling loads by up to 31%, lower indoor temperatures, and extend comfort hours, making them essential for mitigating climate-change-induced overheating [13]. Anand et al. (2023) emphasized their long-term economic viability through low operational costs and lifecycle savings [14]. Active strategies on the other hand, including advanced HVAC systems, ground-source heat pumps, and renewables, meet residual demand but involve higher operational and maintenance requirements [15]. Integrating passive measures first maximizes the effectiveness of active systems while reducing vulnerabilities such as intermittency and system degradation.

Passive cooling design strategies include: High R-value/Low U-value of the Building Envelope, Use of High Solar Reflectance Materials and Coatings on the Building Envelope and Outdoor Surfaces, Continuous Insulation (Thermal Bridge Prevention), Airtightness of Building Envelope Components, Optimal Building Volume to Envelope Surface Area Ratio, Shading, Louvers, and Semi-Transparent Envelope, Cooling Tower, Earth-Sheltered Building, Geothermal Ventilation Pipes, Cross Ventilation and Stack Ventilation, Nighttime Cooling, Elevated Roof, Double Skin Facades, Water Space/pond, Atrium, Shading with Deciduous Plants, Green roof/Green wall, Thermal mass materials.

Passive heating design strategies include: High R-value/Low U-value of the Building Envelope, Continuous Insulation (Thermal Bridge Prevention), Trombe-Michel Wall/thermal mass wall, Sunspace/Solar Atrium, Optimal Building Volume to Envelope Surface Area Ratio, South-Facing Glazing Surfaces, Transpired Solar Wall, Solar Chimney, Earth-Sheltered Building, Geothermal Ventilation Pipes, Shading with Deciduous Plants, Appropriate Opening to Solid Envelope Element Ratio, Thermal mass materials.

Passive lighting design strategies include the following: South-Facing Glazing Surfaces, Main Axis Orientation in the East–West Direction, Stepped or Sloped Mass with South Orientation, Open Spaces (Atriums and Courtyards), Proper Arrangement of Openings (Skylights, clerestories and roof monitors), Daylight Distribution Devices (Light Shelves and daylight ceiling).

Although the literature includes ample evidence for the effectiveness of passive strategies [16,17], their implementation success is very sensitive to local climate and site-specific conditions. Improper application of such strategies can, in fact, reduce rather than enhance a building’s energy efficiency. As Randjelović et al. (2021) highlight, individual strategies may either counteract one another or synergistically improve overall building performance [18]. For example, Vullo et al. (2018) found that overhangs can reduce glare and cooling loads; however, they also increase heating demand and decrease daylight autonomy [19]. This illustrates a design strategy that enhances summer performance but compromises winter performance and lighting availability. Gassar et al. (2021) observed a nonlinear relationship between heating/cooling loads and the orientation and window-to-wall ratio of a residential building—showing that optimizing for one season or function may unintentionally raise energy loads for another [20]. Similarly, Echenagucia et al. (2015) demonstrated that window position and window-to-wall ratio significantly affect both heating and cooling performance, with trade-offs varying across climates, underscoring the importance of context-sensitive design [21].

In addition, the successful implementation of PD strategies can also be potentially affected by a variety of risk factors ranging from incorrect costing assumptions to improper methodologies selection and failures in material application and component assembly [22]. It is thus important to investigate how Greek professionals perceive the effectiveness of PD.

Moreover, according to Waqar (2023), there are numerous reasons for professionals overlooking PD strategies despite the fact that their advantages are well documented and acknowledged [23]. These reasons concern a wide range of factors related to costs, lack of institutional support and enforcement, lack of awareness and skills, strong attachment to poor teamwork practices, resistance to change and low environmental reflects, from both the client and the designer. Along the same lines, Lee et al. (2013) attribute this phenomenon to the lack of sufficient data, architects’ inexperience, and absence of practical guidance [11]. Lee et al. (2021) also point out that energy-efficient passive buildings is a way under-represented topic in university curricula [24]. In this context, it is worth exploring the Greek professional’s perceptions on factors like the aforementioned ones, potentially deterring them from actual PD implementation.

In a more specialized context, the literature sheds light to problematic aspects of simulation tasks for PD. Azizkhani and Haberl (2021) note that passive strategy simulations tend to be complex due to the difficulty of accurately controlling and modeling various dynamic factors that fluctuate throughout the day, which are inherently challenging to replicate in simulation environments [25]. Other research indicates that existing simulation tools are often not architect-friendly and are ill-suited for use in the conceptual design phase, when fast, intuitive feedback is essential [26]. Balali et al. (2023) add that some strategies have been only marginally represented in existing simulation tools and remain difficult to model effectively across different energy simulation software platforms [1]. Despite all the above though, employing building energy simulation at the early stages of design—when decisions regarding building shape, number of stories, and orientation are made—is critical for achieving optimal natural lighting, heating, and ventilation [27]. Therefore, the perceptions regarding the activity of simulation will also be investigated in the survey.

Furthermore, as PD strategies require conceptualization from the very early stages of a project’s development, this definitely leaves behind the traditional fragmented procurement system of Design-Bid-Build and renders necessary the integrative design process (IDP) where project teams have representatives from various disciplines sharing their knowledge, analyses, and ideas from the very beginning [28]. A critical difference in this approach is that team members mutually define the desired outcomes of the project and work together to set performance goals. These goals should be shared and project-centric and not individually determined. Advantages of aligning goals include a shared learning curve for all team members, reduced risk of misunderstandings and inefficient communication, timely assessment of the team skills’ adequacy for the project’s requirements, and a clear path of the future with minimal chances for significant changes [29]. Despite the advantages, this integrative organizational paradigm entails significant managerial complexity [30,31] and is often deliberately ignored or avoided by engineers [5,25]. Therefore, the collaborative aspect required in PD is another area of interest for the survey.

2.2. Building Environmental Performance Certification-LEED

To address the need for a comprehensive system for certifying buildings as green and sustainable, stakeholders worldwide have developed and adopted various certification standards. These include systems such as LEED, Passive House, GBCC, CASBEE, and BREEAM. Each of these frameworks outlines specific criteria related to the surrounding environment, energy efficiency, material use, resource management, and indoor environmental quality—with energy conservation consistently ranked as a top priority [30]. The core principle behind these assessment tools is straightforward: by assigning buildings to specific performance categories, their efficiency in areas such as energy, water, and material use can, at least theoretically, be compared to others within the same classification. This comparability is one of the main reasons these programs have gained widespread appeal. For developers, investors, property owners, and occupants, the idea is intuitive—a building rated five stars or classified as “gold” is perceived as superior to one rated with a single star or labeled “bronze.” Beyond performance evaluation, these systems also serve as powerful tools for marketing, branding, and promoting buildings at the local, national, and international levels [32].

LEED in particular, was created by the US Green Building Council (USGBC), a green building industry coalition founded in 1993 amid an increased cultural focus on environmental concerns. The goal was to create better buildings optimized “with people and nature in mind” [33]. As of 2025, there are about 197,000 LEED-certified projects worldwide, in 186 countries and territories, representing about 2.7 billion square meters of building [7]. Greece’s sustainable building sector is also increasingly affected by LEED. Between 2020 and early 2025, the number of LEED-certified buildings in Greece nearly tripled—from 33 to 90—indicating a dramatic increase in both awareness and implementation of sustainable building practices. Furthermore, this growth trajectory is expected to accelerate significantly. According to the latest available data [34], there are currently more than 270 buildings registered for LEED certification—buildings that are not yet certified but have formally committed to pursuing it. This figure suggests a robust pipeline of projects that will exponentially increase the footprint of LEED in Greece over the coming years. While other certification systems such as Passive House, ENERGY STAR, and BREEAM are also present in the Greek market, current trends suggest a strong and growing preference for LEED. Its adaptability across different building types, international recognition, and alignment with ESG investment strategies have likely contributed to its dominance. Given these developments, it is increasingly evident that LEED is poised to become the defining framework for large-scale building developments in Greece in the near future. This underscores the importance of examining whether LEED certification encourages integration of PD, especially given Greece’s climatic context and the potential benefits of PD strategies.

To achieve LEED certification, a project earns points by adhering to prerequisites and credits that address, among others, carbon emissions, energy, water, waste, transportation, materials, health and indoor environmental quality. Projects go through a verification and review process and according to the points awarded they are categorized as Certified (40–49 points), Silver (50–59 points), Gold (60–79 points) and Platinum (80+ points) [28]. There are eight main LEED assessment categories in its latest version (version 5): Integrative Process, Planning and Assessments, Location and Transportation, Sustainable Sites, Water Efficiency, Energy and Atmosphere, Materials and Resources, Indoor Environmental Quality and Project Priorities [28]. ‘Energy and Atmosphere’ is the credit category that contributes the most to the points potentially obtained, showing that energy is a high priority in LEED [35]. More specifically, this category includes five prerequisites (no points awarded) and six credits totaling 33 points, in the case of new construction. It is, therefore, possible to earn a maximum of 33 points in this category, i.e., 30% of the maximum total points (110 points) that can be earned in the certification [28]. These points can be obtained through energy simulations, measurements, system commissioning, and efficient equipment and systems. Scofield et al., (2021) report that LEED Gold–certified U.S. office buildings were found to achieve statistically significant reductions in source energy use and greenhouse gas emissions compared to non-LEED equivalents, with aggregate savings of 11% in site energy and 7% in both source energy and GHG emissions [36]. However, although LEED can definitely boost energy efficiency, its impact is not universal or guaranteed for all categories of buildings and regions. the actual energy performance of a building depends on factors such as the climatic context and the building’s operational characteristics [35].

2.3. Demystifying the LEED-PD Interaction

Following thorough study of the LEED v5 Building Design and Construction (BD+C) credit structure [28], it was observed that PD strategies can be potentially promoted through the following credit-bearing options. These include:

• Biodiverse Habitat (1–2 points)—Encourages the use of vegetation and thoughtful site planning, measures that can indirectly support better daylight penetration and natural ventilation potential.
• Accessible Outdoor Space (1 point)—Promotes open spaces that can enhance environmental interaction, indirectly supporting daylight access and natural ventilation potential.
• Enhanced Resilient Site Design (2 points)—Recognizes building orientation and passive cooling strategies through natural airflow and shading.
• Heat Island Reduction (1–2 points)—Includes roof and non-roof strategies, covered parking, and tree equity.
• Peak Thermal Load Reduction (up to 5 points)—Achieved through envelope optimization and ventilation strategies, i.e., by minimizing thermal bridging and limiting air infiltration.
• Enhanced Energy Efficiency (up to 10 points, +3 points for simulation validation)—Requires that the building showcases decreased energy consumption when compared to a base model.
• Occupant Experience (Biophilic Environment—up to 4 points; Proximity to Windows for Daylight Access—1 point; Daylight Simulation—up to 4 points)—Relates to the embedment of natural systems, spatial variability, and a broader view of thermal, sound, and lighting design, incentivizing designers to make use of natural lighting.
• Enhanced Refrigerant Management (1–2 points)—Path 1 promotes passive cooling and heating strategies (e.g., natural ventilation, night flushing, thermal massing, solar storage, added insulation) to eliminate refrigerants.
• Fundamental Air Quality (prerequisite)—Allows compliance through the Natural Ventilation Procedure (NVP), in addition to the Ventilation Rate Procedure (VRP) and Indoor Air Quality Procedure (IAQP).
• Resilient Spaces (1–2 points)—Includes provisions for operable windows and passive thermal safety zones to maintain habitable conditions during power outages in both extreme heat and extreme cold conditions.

It should be noted though that not all the credits listed above are fully achievable through passive means alone. In several cases, passive strategies contribute only partially toward compliance, meaning that the total number of points indicated does not directly correspond to the total points achievable solely via PD. Further to the above, IPD, the organizational approach required for effective PD adoption, is rewarded by the credit structure.

Apart from the above, the fourth version of the certification (LEED v4 BD+C) foresees that the residential projects certified by the Passivhaus Institute as ‘Passive Houses’ also earn points [37]. This clearly acknowledges the value of PD. However, as noted by the USGBC [37], PD is an excellent complement to LEED, as PD targets climate-specific comfort and performance, whereas LEED focuses on reducing energy, water, waste, and transportation impacts. This distinction officially confirms that LEED is not primarily designed to incorporate PD principles as a core component—hence the emphasis on their complementarity.

The previous conclusion is also evident in the relevant literature. For instance, Azizkhani and Haberl (2021) refer to inadequate incentives for any conscious early incorporation of complex PD elements in the design process [25], while Chen et al. (2015) point out that, compared to other schemes, LEED places the least emphasis on PD incorporation [4]. Similar points are echoed by Ferreira et al. (2014), who also comment on LEED’s over-reliance on active systems [38]—a view consistently repeated in subsequent studies [4,30,39]. Although these assessments were based on earlier versions of LEED, they still remain directly relevant; LEED v4 (released 2013) continues to dominate certifications in the studied context, with minimal uptake of v4.1 and no v5 projects to date. Furthermore, the recently released LEED v5 does not introduce substantial changes to strengthen PD incentives. Instead, it is framed around three core impact areas—decarbonization, quality of life, and ecological conservation—with a pronounced focus on operational and embodied carbon reduction, electrification, and renewable energy requirements. While v5 includes new credits such as Reduce Peak Thermal Loads, these are embedded in a broader performance-carbon framework rather than in a coherent set of credits aimed at rewarding PD strategies [40]. Thus, the lack of explicit PD support identified in earlier literature appears to typify the current version as well. Furthermore, another noteworthy point is that systems like LEED seek to maintain a degree of universality by standardizing performance metrics that can be applied across diverse climates and regions. This results in them placing a clear emphasis on envelope-related features—such as wall and roof construction, fenestration, insulation, and air-tightness—rather than on supplementary passive systems or context-specific design elements [25]. While this approach enhances the framework’s international reach, it limits its capacity to incorporate traditional, climate-responsive strategies that are often deeply embedded in regional architectural practices. Possibly this is one of the reasons why many countries like Germany, Sweden and Australia, have opted to develop their own sustainability assessment tools—more closely tailored to local environmental, cultural, and regulatory conditions—rather than rely solely on globally standardized systems like LEED.

Overall, the available literature suggests that obtaining LEED certification does not significantly encourage the adoption of PD strategies, nor does it prompt designers to make decisions aligned with such approaches due to limited credits incentivizing PD and a structure that prioritizes standardized, active measures over context-sensitive passive approaches. As both the aforementioned points are of great interest, they will also be included in the survey.

2.4. LEED and PD Research in the Greek Context

The available literature on PD and sustainable building practices in Greece covers a wide range of topics. For instance, Papamanolis (2000) offers a comprehensive analysis of natural ventilation in Greek buildings, grounding their conclusions on actual climatic and construction data [41]. In subsequent works, Papamanolis (2014, 2016) examines the integration of solar energy systems into Greek buildings and particularly differentiates between passive and active applications, identifying architectural constraints, such as dense urban morphology reducing passive solar gains [42,43]. Similarly, Giannadakis et al. (2025) analyze real-time energy data from a certified passive house, using advanced monitoring to evaluate performance across heating, cooling, and air quality parameters [44]. Furthermore, Mytafides et al. (2017) examine passive heating and cooling techniques under Mediterranean conditions in the context on the transformation of a university building into a zero-energy facility [45] while Ascione et al. (2017) demonstrated that integrating passive heating, cooling, and daylighting strategies with renewable energy at the urban-planning stage can achieve near-zero energy demand and high indoor comfort in a Greek seaside settlement [46]. Sakantamis et al. (2020) also showed that site-specific passive measures—such as wind shielding, solar heat gain optimization, and a solar chimney—can enhance thermal comfort and reduce energy use in a mixed-use student center design [47]. Regarding the literature aimed at certification schemes, Giarma et al. (2017), analyze and compare LEED, BREEAM, SBTool, and CASBEE guidelines for daylighting and visual comfort [48] while Papadopoulos and Giama (2009) attempt a comparative analysis of BREEAM and LEED in a Greek office building [49]. Kontoleon et al. (2008) refers to tools like LEED in a general overview of sustainability practices in Greece [50], while Iliopoulos et al. (2018) explores the challenges of implementing LEED in Greece based on interviews with LEED-accredited professionals [51]. This work identifies procedural and material-related barriers, and it does not focus on passive strategies. Karkanias et al. (2010) also focus on systemic barriers to the adoption of bioclimatic design [52].

The current research aims to provide novel insights to the field, by examining the experiences and perceptions of Greek construction professionals with PD implementation and exploring how these strategies interact with the LEED certification framework. This focus is especially pertinent as both passive approaches and environmental certification are gaining momentum in Greece, yet their alignment in practice remains underexplored.

3. Methodology

Following the review of the literature, a close-ended questionnaire survey was designed to elicit the opinions of various construction engineering professionals with experience in sustainable building projects, who are actively involved in LEED-certified building projects or other similar certifications and thus, they share a foundational understanding of sustainability principles and their perspectives. The use of questionnaire has been widely applied to collect professional views in studies relating to green infrastructure and construction (e.g., [53,54,55]).

3.1. Questionnaire Structure and Content

The questionnaire consisted of two sections, the first related to respondents’ background information and the second to their experiences and perceptions in PD and LEED. Specifically, Section A comprises demographic questions, designed to categorize research participants according to their professional background, years of experience, certification status in any sustainable building rating system, and previous involvement in the design or construction of certified sustainable buildings. In section B, the respondents were presented with a total of 17 closed questions informed by a review of relevant literature, with each question corresponding to specific themes, barriers, or gaps identified in the studies discussed in the literature review section. These include, for example, challenges related to knowledge gaps, simulation limitations, or LEED’s treatment of passive strategies. Their inclusion in the survey reflects a deliberate effort to explore whether these internationally recognized issues are also relevant within the Greek context. The questions were distinguished in (i) 10 statements for which the respondents were requested to provide their degree of agreement or disagreement on a five-point Likert scale, a well-established summated rating scale used for measuring attitudes (1 = strongly disagree, 2 = disagree, 3 = neither agree nor disagree, 4 = agree, 5 = strongly agree) and (ii) 7 multiple choice questions where respondents had to pick one or multiple options. The questions are presented in the tables within the Results section, grouped by category; however, this does not reflect the original order in which they appeared in the questionnaire.

The 10 Likert-scale statements were designed to explore attitudes and perceptions regarding PD strategies and specifically their implementation in practice and their perceived benefits (statements 1–3) as well as barriers (statements 4–7). Several items also focused on perceptions related to the integration of PD in the LEED credit structure (statements 8–10). The Likert scale was selected as it is well-suited for exploring favorable or unfavorable attitudes toward key concepts. Additionally, its user-friendly format tends to encourage participation, thereby improving response rates and enhancing the reliability and generalizability of the findings [56]. To calculate the average level of agreement (ALA) for each statement, a weighted mean was used. Specifically, the frequency of each response option (i.e., scores from 1 to 5) was multiplied by the corresponding score value. The products were then summed, and the total was divided by the number of respondents (n = 89). This method yields the mean score for each item, reflecting the overall tendency of the sample toward agreement or disagreement.

Similarly, the multiple-choice questions aimed to identify commonly used PD strategies (questions 1–3), investigate relevant professional practices related to collaboration and energy simulation—both of which are critical for PD successful integration—(questions 4, 6, 7) and further examine perceptions related to the PD integration in the LEED credit structure (question 5). These questions were either ‘list’ questions where the respondents were requested to select multiple options that reflected their views, or ‘category’ questions where only a single response could be selected [57]. For the multiple-choice questions, descriptive statistics were used, and results are presented as the percentage of respondents who selected each available option.

3.2. Questionnaire Testing and Distribution

As Gray (2004) notes, careful phrasing—ensuring that questions are clear, concise, unambiguous, and free of jargon or abbreviations—can significantly enhance the clarity and effectiveness of the instrument across the sample population [57]. For this purpose, piloting a questionnaire is a valuable step in identifying and reducing questions that may cause confusion or misinterpretation. In the case of the current research, a draft version of the questionnaire was reviewed by two experienced professionals in sustainable design and one academic with expertise in environmental performance and certification systems. Their feedback helped refine the wording of items, improve clarity, and ensure the practical relevance of the content. Minor modifications were made based on their suggestions before final distribution.

The final version of the questionnaire was distributed online, primarily via LinkedIn and direct email communication, targeting professionals active in architecture, engineering, and construction with relevant experience in sustainable design and certification systems. A convenience sampling approach was adopted, but inclusion was restricted to participants with demonstrable involvement or interest in sustainable building practices. A total of 250 electronic invitations were distributed, yielding 89 valid responses which resulted in a response rate of 35.6%. Since the questionnaire was administered via an online form, all responses were automatically recorded in an online database. As noted by Perez et al. (2017), the use of such databases offers several benefits, including eliminating the need for manual data transcription, minimizing errors, simplifying data retrieval for statistical analysis, and enabling data mining to uncover inferred or derived insights [58].

3.3. Respondents Demographics

A central aim of this research was to ensure the inclusion of the various professional disciplines involved in the development of green buildings. This was effectively achieved as the survey attracted all the three primary professional categories listed, i.e., architects (34%), civil engineers (28%), and electromechanical engineers (30%). In addition, participants had the option to specify their profession if it did not align with any of these three predefined categories. This flexibility led to the inclusion of a broader range of expertise within the sample, including four building physicists, an acoustic consultant, a chemical engineer, an interior architect, two natural environment engineers, a sustainability consultant, and an environmental/ESG consultant (8%). The demographics indicate a balanced representation across the main professional groups and thus, the findings can be considered a well-rounded reflection of the perspectives within the sustainable and green building sector. Τhe absence of ‘Facility/Building Manager’ from the research sample is not surprising as in contrast to more mature markets such as the UK and Germany, in Greece, the role of the Facility Manager has not yet been established as a distinct and institutionally recognized professional occupation. In fact, the Facility Management (FM) sector is still at a developing stage [59] with only 22 member companies in the national association [60]. In comparison, the UK FM sector which is one of the most mature and structured in Europe, employs 1.2 million people [61]. Therefore, the current structure and professional maturity of the FM sector in Greece do not realistically support the systematic inclusion of Facility Managers in research frameworks focused on specialized certification schemes such as LEED. Furthermore, among the respondents, 11 individuals (12.4%) reported having 1–5 years of experience, 32 (35.9%) had 6–10 years, 22 (24.7%) had 11–15 years, and 24 (27.0%) had more than 15 years of experience. Incorporating a significant number of accredited professionals was a key objective, given that such individuals are, by definition, more familiar with the methodologies and practices involved in the design and realization of certified sustainable buildings. This objective was successfully met as out of a total of 89 participants, 34 are LEED-accredited professionals, while an additional 12 hold certifications in other sustainability assessment frameworks. In total, 51.6% of respondents are certified in at least one recognized sustainability assessment system.

4. Results and Analysis

4.1. Descriptive Statistics

The questionnaire was designed with the aim to highlight the popularity of specific PD applications, investigate professional perceptions on PD strategies and shed light on specific implementation aspects of LEED which could promote passive strategies.

Table 1. Ten statements of questionnaire and relevant results.

	Statement for Evaluation on a 1–5 Likert Scale (Strongly Disagree–Strongly Agree)	ALA
St. 1:	Passive design systems present an opportunity for greater architectural creativity and sustainability benefits	4.72
St. 2:	Based on your knowledge/experience, passive design strategies are effective in achieving energy efficiency.	4.07
St. 3:	Bioclimatic criteria are considered when determining new building orientation and form	3.18
St. 4:	The lack of appropriate knowledge and experience in the project team is a significant barrier for passive design strategies integration	4.15
St. 5:	The increased organizational complexity inherent in the collaborative processes required for the effective integration of passive design strategies is a barrier for their implementation	3.54
St. 6:	The difficulty in developing appropriate energy simulation models for passive design elements is a significant barrier for their integration	2.78
St. 7:	The lack of sufficient evidence regarding the performance of passive design elements is a significant barrier for their integration	2.19
St. 8:	The lack of sufficient incentives (credits) for including passive design elements within environmental certifications like LEED is a significant barrier for their integration	2.97
St. 9:	LEED’s credit system favors active design strategies at the expense of the passive ones	3.53
St. 10	LEED presents a standardized structure which prevents it from promoting locally effective passive design strategies	3.88

and

Table 2. Seven multiple choice questions and relevant results.

Multiple Choice Questions	Choices	Result
Q1 Which of the following passive cooling systems have you used in your designs or observed in a project you have worked on?	many	Figure 1
Q2 Which of the following passive heating systems have you used in your designs or observed in a project you have worked on?	many
Q3 Which of the following passive lighting systems have you used in your designs or observed in a project you have worked on?	many
Q4 Have you participated in a project where “Integrative Design Process” was implemented?	Y/N	Yes 60% No 40%
Q5 Should a proportion of LEED credit points be assigned to passive design strategies that are effective in the local context of the building?	Yes Yes but it would be difficult to implement No	Yes 58.4% Difficult 39.3% No 1.1%
Q6 In the context of pursuing LEED certification, how do you prefer to earn the credit for Enhanced Energy Efficiency (EAc3)?	Simulation/Prescriptive/don’t know	Sim 49.4% Prescr 8.6% Don’t know 42%
Q7 When is the right time for the development of energy simulation scenarios in a new building design?	architectural concept design stage/final phase of architectural study/when active energy systems are designed	Concept 77% Final phase 14% With active 9%

present all questions and relevant results.

The first question aimed to capture whether participants hold a positive disposition toward PD systems. The question was answered on a 1–5 Likert scale for agreement as follows: 83 (93%) strongly agreed/agreed that PD systems present an opportunity for sustainability benefits combined with a greater architectural creativity, while 6 (7%) were neutral or disagreed/strongly disagreed with this perspective. The ALA for this question was found to be equal to 4.72/5; therefore, a very strong confirmation was observed. In the same vein, the second question aimed to assess if PD is perceived as an effective option for enhanced energy efficiency. The responses indicated strong agreement, with a high ALA = 4.07 representing agreement of 78.7% of the respondents. The third question focused on the participants’ experience on the consideration of bioclimatic criteria when the orientation and the form of a new building are determined. Interestingly, only 37 respondents (41.6%) agreed or strongly agreed that bioclimatic criteria are considered in practice while the majority (58.4%) indicated that these criteria are generally overlooked, leading to an overall ALA = 3.18. Figure 1 illustrates the previously described gap between the theoretical acceptance of passive building design and its actual implementation in practice.

Then, three multiple choice questions were posed to capture the participants’ experience regarding the most frequently used passive systems. These questions evaluated the extent to which each one of the PD strategies of the given list has either been employed by Greek professionals themselves or observed in projects they have participated in. The strategies were categorized into passive cooling systems, passive heating systems, and passive lighting systems.

The options for cooling included: Continuous Insulation (Thermal Bridge Prevention), Airtightness of Building Envelope Components, Optimal Building Volume to Envelope Surface Area Ratio, Shading, Louvers, and Semi-Transparent Envelope, Cooling Tower, Earth-Sheltered Building, Geothermal Ventilation Pipes, Cross Ventilation and Stack Ventilation, Nighttime Cooling, Elevated Roof, Double Skin Facades, Water Space/pond, Atrium, Shading with Deciduous Plants, Green roof/Green wall.

The options for heating included: High R-value/Low U-value of the Building Envelope, Continuous Insulation (Thermal Bridge Prevention), Trombe-Michel Wall/thermal mass wall, Sunspace/Solar Atrium, Optimal Building Volume to Envelope Surface Area Ratio, South-Facing Glazing Surfaces, Transpired Solar Wall, Solar Chimney, Earth-Sheltered Building, Geothermal Ventilation Pipes, Shading with Deciduous Plants and Appropriate Opening to Solid Envelope Element Ratio.

The option for lighting included: South-Facing Glazing Surfaces, Main Axis Orientation in the East–West Direction, Stepped or Sloped Mass with South Orientation, Open Spaces (Atriums and Courtyards), Proper Arrangement of Openings (Skylights, clerestories and roof monitors), Daylight Distribution Devices (Light Shelves and daylight ceiling). Figure 2 presents the most popular options per category.

In the category of cooling, 85.4% of the respondents highlighted the popularity of continuous insulation (thermal bridge prevention), while the option of shading, louvers and semi-transparent envelope came second with 82% and the option of green roof/green wall, third with 77.5%. Other popular options included high R value- low U-value of the building envelope (68.5%), use of materials and coatings with high solar reflectance (58.4%) and inclusion of atrium (43.8%). The options that were placed at the bottom of the list included geothermal ventilation pipes (14.6%), double-skin facades (11.2%), and elevated roof (7.9%). Similarly, the most popular design options in the category of heating were found to be the high R value–low U-value of the building envelope (84.3%), the continuous insulation (thermal bridge prevention—70.8%) and the south-facing glazing surfaces (51.7%). The least recognized options in this category included the transpired solar wall (9%), the thermal mass wall (9%) and the solar chimney (5.6%). It is evident from the responses that the multitude of well-tested options for heating are less than those for cooling, with the category attracting an overall lower attention from the Greek professionals.

In the third category of lighting, the highest recognition was given to open spaces (atriums and courtyards) by the 68.5% of the respondents, the option of south-facing glazing structures was placed second with 62.9%, while proper arrangements of openings (skylights, clerestories, roof monitors) was ranked third with 57.3%. Other options with considerable recognition were the orientation at east–west direction (41.6%) and daylight distribution devices (31.5%). The least popular option was the sloped mass with south orientation (18%). It can be observed that Greek professionals showed an overall higher awareness for the various design options of this category (lighting) and the level of popularity of the options presented lower variance compared to the other two categories (heating, cooling). The next question sought to find out if respondents have participated in a project designed as per the IDP. Moreover, 60% of the respondents confirmed that they have experience in IDP while 40% did not (Table 2).

Following these questions, a series of 7 statements were given for the respondents to indicate their level of agreement on a 1–5 Likert scale. The first 5 questions (st. 4–8 of Table 1) were related to factors potentially having a deterrent effect to the PD implementation in Greek buildings.

The results for these questions showed that the respondents strongly confirm that the lack of appropriate knowledge and experience is a significant barrier (ALA = 4.15) followed by the organizational complexity accompanying collaborative PD which is also moderately accepted as a barrier with ALA = 3.54. The remaining factors with potentially deterring effect were given lower scores, indicating that the respondents’ perceptions were not very supportive of the literature observations. Specifically, the view that the energy simulation models for PD are difficult to develop was strongly confirmed only by 21 respondents (24%), while the remaining 68 were either neutral (21%) or negative towards this view. The average score representing the ALA for this statement was 2.78/5. Similarly, the respondents did not support the view that there is lack of sufficient evidence of PD elements’ effectiveness (ALA = 2.19). This way they further reinforced their positive stance toward the integration of PD strategies in building design. Concerning, however, the lack of sufficient credits in environmental certifications for PD and how this discourages its implementation, the responses were not particularly conclusive; 24 of the participants recognized this factor as a significant barrier, another 21 were neutral and the remaining 44 disagreed with the statement. This distribution of answers led to ALA = 2.97, indicating overall neutrality.

The next two questions were specifically focused on the LEED-PD interface and sought to gather opinions on two frequently encountered criticisms: firstly, that the LEED’s credit system favors active design strategies at the expense of the passive ones and secondly, that LEED presents a standardized structure which prevents it from promoting locally effective PD strategies. Regarding the overreliance of LEED to active systems, 53% of the respondents agreed/strongly agreed, 36% were neutral and only 11% disagreed. This means that the overall tendency of the experts was towards the acceptance of the view that LEED’s credit structure discourages the selection of PD systems (ALA = 3.53). Regarding the view that LEED presents a standardized structure which disregards the building location’s characteristics and fails to leverage locally effective PD strategies, the survey’s respondents were by 54% in favor of the statement, another 32% were neutral and the remaining 14% was negative. The ALA was equal to 3.88 signifying that Greek professionals do not reject the existence of the barrier but do not confirm it as a strong one either.

Aiming to investigate perceptions in greater detail, the next question was seeking to investigate the professionals’ feedback on the potential for a specific percentage of LEED credit points be awarded for PD elements that have been proven effective in the country/region of the building. Notably, 88 out of 89 respondents regarded this as a worthwhile action; however, a significant portion (39%) acknowledged that its implementation would present considerable challenges (Table 2).

The last two (multiple-choice) questions of the survey focused on technical aspects of LEED implementation, specifically the methods used to achieve the credit for Enhanced Energy Efficiency (EAc3) in the context of pursuing LEED certification, and the preferred stage for integrating energy simulation (Table 2). The question regarding EAc3 aimed to capture Greek professionals’ preference between the two alternative ways provided by LEED for demonstrating a building’s energy efficiency, i.e., the simulation path and the prescriptive path. Having a reliable indication for this preference helps determine the stages where it is worthwhile to promote PD. Due to the specialized nature of this question, a “Do not know” option was also provided, which was selected by 37 respondents (42%). Therefore, the 44 respondents who indicated a preference for the simulation path represented 85% of those who were able to answer the question.

Finally, the last multiple-choice question sought respondents’ views on when the right time for development of energy performance scenarios of a new building, is. The options included as early as the architectural concept design stage, later during the final phase of architectural study, or even later during the design of active energy systems. The vast majority of respondents (76%) supported initiating energy simulations at the earliest possible stage.

4.2. Inferential Statistics

Inferential statistics enable a deeper understanding of the data by facilitating the examination of underlying relationships, testing hypotheses, and drawing conclusions that extend beyond the immediate sample; in this context, their application enables the quantitative exploration of the observed gap between the theoretical acknowledgment and the actual implementation of PD principles.

4.2.1. Associations Between Perceptions

The non-parametric test of Spearman’s rank-order correlation was used with the aim of assessing the relationships between the respondents’ theoretical acceptance of PD principles and their reported perceptions of perceived barriers. This test was selected due to the ordinal nature of the data (Likert-scale responses) and the non-normal distribution of the variables. The correlation results revealed two statistically significant associations: First, there was a moderate negative correlation between respondents’ belief in the effectiveness of PD strategies in achieving energy efficiency (Statement 2) and their perception that a lack of sufficient evidence regarding the performance of PD elements constitutes a significant barrier (Statement 7), with a correlation coefficient of rs = −0.283 and a p-value of 0.0072. This indicates that respondents who have higher confidence in the effectiveness of PD principles tend to report fewer concerns about insufficient evidence as an obstacle to their integration. Conversely, those who are less convinced of PD effectiveness tend to perceive the lack of evidence as a more significant barrier. Second, a moderate positive correlation was observed between the actual consideration of bioclimatic criteria in practice (Statement 3) and the perception of increased organizational complexity inherent in the collaborative processes required for effective PD (Statement 5), with rs = 0.312 and a p-value of 0.0029. This implies that professionals who actively apply bioclimatic design principles are more likely to recognize and report organizational complexity as a barrier to implementation. This reflects the practical reality that integrating PD strategies often involves complex collaboration among multiple stakeholders, which can challenge the smooth adoption of such sustainable practices.

4.2.2. Influence of Professional Background and Experience on Perceptions

To explore whether respondents from different professional backgrounds (specifically, architects versus other professions) perceive key issues differently, a series of Mann–Whitney U tests were conducted. This non-parametric test was chosen due to the ordinal nature of the Likert-scale data. For each of the ten relevant survey statements, the distributions of responses between architects and non-architects were compared (

Table 3. Results of the Mann–Whitney U Tests Assessing Statistically Significant Differences between different groups of respondents (α = 0.05).

Statement	1	2	3	4	5	6	7	8	9	10
Grouping criterion: Profession (architects vs. other professional roles)
Statistically significant difference	N	Y *	N	N	Y **	N	N	N	N	N
* Architects support more strongly that passive design strategies are effective in achieving energy efficiency ** Other professionals support more strongly that the organizational complexity inherent in PD is a barrier
Grouping criterion: LEED accreditation status (accredited vs. non-accredited)
Statistically significant difference	N	N	N	N	N	N	N	N	Y *	Y **
* Accredited professionals support less strongly that LEED favors active systems ** Accredited professionals support less strongly that LEED is not adaptable to local PD strategies
Grouping criterion: years of experience (more than 10 years vs. less than 10 years)
Statistically significant difference	N	N	N	N	N	N	N	N	N	N

—In the table, ‘Y’ denotes Yes and ‘N’ denotes No). In two out of ten cases, the differences were found to be statistically significant at the 0.05 level. In greater detail, the results for statement 5: “The increased organizational complexity inherent in the collaborative processes required for the effective integration of passive design strategies is a barrier for their implementation”, indicated a statistically significant difference (Z = −2.23, p = 0.026) in how strongly architects and non-architects perceive organizational complexity as a barrier. A statistically significant difference was also observed between architects’ and non-architects’ responses to statement “Based on your knowledge/experience, passive design strategies are effective in achieving energy efficiency” (Z = 2.35, p = 0.019). These results suggest that architects perceive PD as more effective in delivering energy efficiency compared to other professionals, while also appearing less deterred by the organizational complexity it entails.

Similarly, a series of Mann–Whitney U tests were conducted to examine whether LEED accreditation status influenced respondents’ perceptions. Specifically, following a series of tests across all the ten statements, it was found that the accredited professionals were found to have a statistically different level of agreement compared to the non-accredited respondents in two of them (Table 3). These are: Statement 9 “LEED credit systems favour active design strategies at the expense of passive ones,” and Statement 10 “LEED presents a standardized structure which prevents it from promoting locally effective passive design strategies,” (Z = −2.04, p = 0.042 and Z = −2.49 p = 0.013, respectively). These findings suggest that accredited respondents were less inclined to view the LEED’s credit structure as biased against PD and also less critical of the system’s (lack of) adaptability to local passive strategies.

Finally, professional experience was also used as a basis for comparison to investigate whether statistically significant differences existed between the perceptions of senior (>10 years of experience) and junior professionals. However, no statistically significant differences were identified (Table 3).

5. Discussion

The results of this survey reveal that in the Greek context, although PD strategies are widely acknowledged as an effective option for energy efficiency, this however does not translate into commensurately high level of adoption. This confirms Andrea et al.’s (2020) findings who note that usual criteria of design among Greek architects are the better utilization of the plot and the view from the rooms, resulting into about only 1 to 5 buildings having the correct orientation [62]. The gap between the perceived benefits of PD strategies and the practices actually put in place is not observed only in Greece. A similar trend has been reported for Malaysia, India, Pakistan, China [23] and Cyprus [63], among others. This confirms Lee et al.’s (2015) opinion for surprisingly limited use of PD strategies, especially taking into account how effective as well as necessary they are [30]. The results also confirm that the sector’s reluctance to implement PD does not relate to any skepticism of its effectiveness but it rather reflects the occurrence of various deterring factors, with the lack of appropriate knowledge and awareness being the most important one. This reflects literature findings from previous surveys [24,62,64].

In the Greek context, this lack could be attributed to many factors, with educational curricula for Architects reasonably being on the spotlight. Alexandrou et al. (2020) evaluate the undergraduate course for Architects ‘Special Topics on Environmental and Bioclimatic Design’, offered by the School of Architecture at Greece’s most important technological university, the NTUA, and point out that building simulation tools are not fully adapted to standard design studio practice. As a result, it becomes difficult to run all the necessary simulations and reach qualitative and synthetic conclusions, within the time constraint of the regular 13-week semester [65]. Giannarou (2020) also emphasizes the need of introducing sustainable design courses at Greek universities and organizing awareness campaigns on bioclimatic buildings [66]. Therefore, there is a clear indication that bioclimatic principles should be given greater attention in the Greek tertiary education. Fernandez-Antolin et al. (2022) add that there is a similar lack with regard to Building Performance Simulation Tools which have not yet been meaningfully integrated into the curricula of architectural education worldwide [67]. This results in a persistent disconnection between architectural students and energy simulation practices, despite the acknowledged importance of energy modeling during the early design stages.

Further to the above, the lack of knowledge turns into a vicious cycle by the fact that Architects are seldom requested to practice such measures, due to the client’s lack of interest. This is justified by the fact that, as Azizkhani and Haberl (2021) point out, any technological or design intervention, which is different from the business-as-usual practices, including passive systems, will be seen by clients as an additional cost for a project [25]. This combination of educational gap and unwilling clients is also noted by Giannarou (2020) in her study on educating Greek Engineers in the design of bioclimatic buildings [66].

Moreover, the respondents also confirmed that a factor that deters them from engaging in collaborative practices required for successful PD adoption, is the perceived complexity of the integrative processes—this was more strongly confirmed by the non-architect professionals. In any case, the positive association between implementation and organizational complexity underscores the need to address collaborative challenges in project management to facilitate sustainable design integration. The penetration of the collaborative paradigm in the Greek private sector is difficult to be assessed given that there are no relevant data available. Additionally, 60% of the respondents who confirmed having participated in such a collaborative scheme seems to be an overly optimistic figure which would need further validation especially in relation to the relevant contractual arrangements. Furthermore, the use of BIM, which is strongly related to effective stakeholders’ interaction, collaboration and efficient decision making [68,69] although the most commonly used technology of the 4th Industrial revolution among Greek construction practitioners, is still at an early adoption stage [70]. Actually, a recent national strategy for BIM issued by the Ministry of Transportation and Infrastructure aims to initiate pilot projects for the use of BIM in public works within the next 2.5 years. Furthermore, the whole industry lacks the required collaborative culture as the national/European legislation does not particularly encourage collaborative schemes for public works and additionally, no structured framework for early contractor involvement has ever been implemented in the country [54,71]. In this context, there are various aspects of the collaborative framework that need further investigation, so that a clearer picture for the actual depth and organizational features of collaborative practices in the Greek context can be obtained. Regarding the ease of use and effectiveness of simulation models, the respondents did not confirm the concerns of the literature. However, this is strongly dependent on personal skills and as already mentioned, the participants of the survey had been chosen for their experience in the field which, from the beginning, places them ahead the average Greek architect or civil/mechanical engineer. Moreover, as Chronis et al. (2012) explain, not all PD models are of the same level of complexity [64]. For instance, they find that the management of solar energy in building design is satisfactorily supported by existing software while wind is hard to quantify, visualize and manipulate; it needs simulations based on computational fluid dynamics and the modeling required is overall very time consuming.

Regarding LEED and its allegedly biased credit structure in favor of active systems, the respondents recognized this tendency but did not evaluate it as a strongly significant barrier. In addition, LEED-accredited professionals had a more favorable view of the certification system’s capacity to support PD, possibly due to deeper familiarity with its structure and flexibility in practice. Similarly, the clear preference of the respondents for the energy simulation path—well linked to PD practical implementation—over the prescriptive path, strongly demonstrates that the current practices in the sector are conducive for greater adoption of passive strategies. Furthermore, the overwhelming agreement among respondents that energy simulations should begin as early as the concept design stage, reinforces the notion that Greek professionals hold a mindset conducive to the adoption of PD strategies. This highlights the clear need for appropriate incentives to help translate this theoretical understanding into practical implementation.

The strongest confirmation of the survey concerns the idea that LEED should be more flexible so as to include locally effective passive strategies in its credit structure. Indeed, the bioclimatic literature explains how the local conditions determine the appropriateness of specific PD strategies [72]. Therefore, it is no surprise that research around specific options is typically accompanied by the local climate conditions they are appropriate for (e.g., for severe cold climate zone in the northwest of China [73], cool-humid zone of north east India [74], Indonesia tropical region [75], hot summer and cold winter zone of China [76]). In addition, there are other less popular sustainability assessment tools (some of which are in use in Greece), like BREEAM, BEAM PLUS and CASBEE, that are much more accommodating to the incorporation of PD strategies—as noted by [4]. BREEAM supports PD by rewarding strategies like thermal comfort, daylighting, ventilation, and building form optimization. CASBEE promotes it through assessments of thermal load reduction with insulation, shading, solar gain, and natural lighting and ventilation. BEAM Plus incorporates PD via site planning, orientation, envelope performance, and natural ventilation and daylight criteria, integrating these into overall energy efficiency.

In the context of the LEED’s global practice, there are indeed various aspects indicating that regional customization is applicable. For instance, Canada has successfully localized the LEED certification system in the past (2002–2022), through a nationally tailored framework known as LEED Canada, developed by the Canada Green Building Council (CaGBC) to reflect the country’s unique climate, regulatory standards, and construction practices. A key feature is the region-specific credits, further differentiated for urban and rural areas as well as the replacement of U.S.-centric credit requirements with Canadian-equivalent standards [77]. In fact, LEED’s “Regional Priority” (RP) credits are intended to address environmental issues that are location-specific. In this direction, USGBC has worked with local volunteers and experts to identify six RP credits for every location—and every rating system—within local or national boundaries. The relevant zones are defined by priority issues—for example, an urban area dealing with an impaired watershed [78]. This approach is strongly appraised by Suzer (2015) who points out that it is a social responsibility for certification bodies to motivate candidate project teams to consider regional environmental issues [79]. Particularly for Athens, the six recognized priority issues are “Optimize Energy Performance,” “Protect or Restore Habitat,” “Rainwater Management,” “Thermal Comfort,” “Sensitive Land Protection,” and “Light Pollution Reduction.” Furthermore, the literature evidence suggests that integrating region-specific criteria in the LEED system can indeed alter the way certification functions, benefiting the specific region. For instance, Pushkar (2018) examined the impact of RP credits on LEED-certified projects in Turkey, Spain, and Italy, and observed that while performance in categories without RP points was consistent across all three countries, performance in categories with RP points varied significantly [80]. This suggests that including RP credits influenced how LEED certification was pursued in different regional contexts.

Recommendations

To address the gap between theoretical support for PD and its limited practical implementation in Greece, targeted actions are needed at education, industry policy and certification levels.

Education: Starting from education, architectural curricula should be revised to embed PD principles and building performance simulation tools more meaningfully into core design studio courses, with adequate time and resources to support their application. Additionally, funding incentives should be provided to universities to develop relevant educational material and tools through targeted research proposals and competitive grants. Beyond undergraduate education, Continuing Professional Development (CPD) programs focused on passive strategies and simulation tools should be expanded and certified. Additionally, PD modules could be incorporated into the increasingly popular postgraduate construction management programs recently introduced by Greece’s leading Universities for engineering studies -NTUA and AUTH-, thereby enabling a wider range of professionals to engage with the subject. Furthermore, organizations such as the Sustainable Building Council Greece can play a pivotal role in developing national guidelines, offering training, and promoting awareness campaigns that communicate the long-term benefits of passive strategies to clients and developers—helping to counter the perception of such measures as mere cost add-ons.

Industry policies: Looking at the organizational perspective, a key requirement towards the early interdisciplinary team formulation is the appropriate contract mechanisms [29]. In this context, standardized collaborative contract models should be adopted to support shared risk/reward mechanisms, incentivize performance-based outcomes, and facilitate early interdisciplinary engagement. In this direction, existing international frameworks such as NEC4 (UK) and IPD agreements could be reviewed and adapted to the Greek legal and procurement environment. These contracts already incorporate mechanisms for shared financial risk and gains, early team integration, and performance-based collaboration. In parallel, early contractor involvement should be institutionalized through legal reforms, enabling more effective participation of contractors during the design phase via mechanisms such as competitive dialog or integrated design–build. Furthermore, the national BIM strategy provides a timely opportunity to pilot such integrated approaches in public projects, therefore collaboration and BIM use should be mandated and systematically evaluated. Finally, public procurement frameworks must evolve to include evaluation criteria that reward collaboration-oriented proposals—such as integrated teams, joint performance goals, and digital coordination platforms—aligning with EU priorities for value-based procurement and sustainable construction delivery. This is a particularly critical point, as it offers a more immediately applicable solution and provides a strong incentive for the sector to move toward collaborative arrangements. Finally, integrating PD incentives into national building codes and procurement frameworks could provide the regulatory push needed to normalize their adoption across both public and private projects. This is especially significant given that these PD incentives could be introduced in place of the environmental provisions of the 2012 New Building Regulations (NOK) which were recently declared unconstitutional by Greece’s highest administrative court.

LEED Certification scheme: The existing experience in regional customization of the LEED scheme could be the steppingstone for the development of a customized assessment framework structured around PD-relevant criteria generated on a regional basis. This flexible approach is already implemented within alternative certification schemes as previously mentioned. Therefore, LEED, with its universal reach and solid procedures, could strengthen its framework by incorporating lessons from these tools that more directly encourage PD.

Furthermore, LEED should preferably reward an integrated package of passive features instead of isolated options as a holistic PD approach is a more effective way to improve a building’s energy efficiency [4]. For instance a combination of orientation, thermal mass, shading and ventilation could be evaluated under a single holistic credit under Sustainable Sites (SS) or Energy and Atmosphere (EA). This would reflect the inherent strength of passive strategies to deliver greater benefits when applied through integrated design. Furthermore, Regional working groups—comprising architects, engineers, local authorities, and community stakeholders could be formed to propose region-specific PD modules within LEED (e.g., optimized courtyards, solar shading, natural ventilation suited to local winds). LEED could then incorporate these as optional “regional adaptations” under Innovation or Regional Priority credits. Similarly, since LEED for Homes awards up to 20 points for achieving Passive House certification, the current practice for residential buildings has already paved the way for non-residential buildings, such as offices, to include PD criteria in their LEED credit structure. In order though to enable the meaningful integration of context-specific bioclimatic design criteria, local authorities should also be activated towards developing appropriate PD criteria, derived from each region’s specific climate and building traditions. These bottom-up, locally led frameworks will help empower stakeholders who understand local climate and cultural context, and also help educate those who do not.

Finally, as LEED certification relies extensively on ASHRAE standards for both the implementation and evaluation of numerous credits, it is to be noted that as of 2025, ASHRAE is preparing to release a new standard—ASHRAE 227—dedicated exclusively to codifying passive building strategies [81]. This forthcoming standard emphasizes reducing heating and cooling loads through passive measures, lowering overall energy use, ensuring airtight construction, eliminating thermal bridges without increasing moisture risk, and effectively managing solar gains. Given LEED’s long-standing reliance on ASHRAE standards, the release of ASHRAE 227 presents a valuable opportunity for LEED to strengthen its support for PD by integrating this new standard into its framework.

6. Conclusions

This study examined the intersection of PD strategies and sustainability certification systems, with a particular focus on the application of LEED in a Greek context. Through a questionnaire survey completed by 89 experienced professionals, it aimed to evaluate the extent to which passive bioclimatic principles are understood, integrated, and rewarded within current sustainable building practices in Greece. Although the analysis is focused on Greece, the findings and recommendations are highly relevant to other Mediterranean and comparable climatic regions, where similar environmental conditions and building practices shape the applicability and effectiveness of PD strategies within certification frameworks such as LEED.

The questionnaire results reveal that the vast majority of professionals view PD not as a constraint but as an architectural opportunity. However, this potential remains largely untapped due to a lack of awareness and appropriate education among key stakeholders. This knowledge gap has understandably resulted in limited practical experience among engineers, reinforcing a vicious cycle that further discourages the adoption of passive systems. With regard to the collaborative framework necessary for the effective integration of PD, respondents demonstrated a moderate awareness of the integrative paradigm, coupled with concerns about its inherent complexity. Given the significance and multidimensional nature of this issue, further research is needed to clarify the specific practices currently applied in the Greek construction sector and to assess the extent to which such collaborative approaches have been integrated to date. Finally, the survey findings strongly support the notion that the LEED credit structure should evolve to allocate specific credits to PD strategies that have proven effective in local contexts—mirroring the existing ‘regional priority’ credits awarded for addressing location-specific environmental challenges.

Furthermore, inferential statistical analyses revealed that enhancing awareness and evidence dissemination could reduce hesitation to adopt PD. A positive correlation also emerged between the active application of bioclimatic criteria and the recognition of organizational complexity as a barrier, underscoring the practical challenges of collaborative processes. Differences in perceptions were evident between architects and other professionals, with architects perceiving PD as more effective and less hindered by collaboration complexity. Similarly, LEED-accredited professionals tended to view the certification system as less biased against passive strategies and more adaptable to local contexts compared to non-accredited peers. However, years of professional experience did not significantly influence perceptions, indicating that attitudes toward PD and LEED may be more shaped by professional role and certification status than seniority.

To address the gap between theoretical support for PD and its limited practical use in Greece, actions are needed at education, industry and certification levels. Firstly, architectural curricula should embed PD principles and simulation tools more meaningfully, supported by funding incentives while CPD courses and postgraduate modules on passive strategies should also be introduced. Organizations and industry bodies can also play a key role in providing guidelines, training, and awareness campaigns to promote the long-term benefits of PD. Furthermore, at the industry level, adopting standardized collaborative contract models, widely used internationally, is key to supporting shared risk/reward and early interdisciplinary collaboration. The national BIM strategy should also be used to pilot integrated approaches in public projects and public procurement should evolve to reward collaboration-focused bids, incentivizing change. Moreover, integrating PD incentives into building codes and procurement is critical, especially since the environmental incentives of the Building Regulations were recently annulled by Greece’s highest administrative court. Finally, LEED certification could expand by embedding region-specific PD criteria into RP or Innovation credits through local stakeholder groups of architects, engineers, and authorities. Furthermore, rather than rewarding isolated measures, LEED should credit integrated PD packages that improve performance more effectively, building on the Passive House pathway for residential projects. Finally, the forthcoming ASHRAE 227 standard on passive buildings offers LEED a timely chance to strengthen PD integration in its framework. In light of these recommendations, it becomes clear that LEED has the structural and institutional potential to become a more robust enabler of bioclimatic architecture.

Building on the findings of this study, future research could focus on assessing the educational and training needs of key stakeholders in order to design targeted programs that enhance PD awareness and competence across the Greek construction sector. Detailed comparative analyses of LEED and other international certification systems, such as BREEAM or CASBEE, may also provide valuable insights into alternative ways of integrating and rewarding passive strategies. Furthermore, exploring the challenges of implementing collaborative models like IDP in Greece could help identify organizational and cultural barriers to the early-stage integration of PD. Lastly, future work could examine the potential for developing a regionally adapted credit system within LEED to support the development of tailored national policies and reward effective passive strategies in the Mediterranean area.