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Article

Leadership in Energy and Environmental Design for LEED Version 4 (LEED-EB v4) Gold Certification Strategies for Existing Buildings in the United States: A Case Study

by
Svetlana Pushkar
Department of Civil Engineering, Ariel University, Ariel 40700, Israel
Buildings 2025, 15(7), 1080; https://doi.org/10.3390/buildings15071080
Submission received: 30 January 2025 / Revised: 25 March 2025 / Accepted: 26 March 2025 / Published: 27 March 2025
(This article belongs to the Section Building Energy, Physics, Environment, and Systems)
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Abstract

:
Identifying factors that influence the choice of Leadership in Energy and Environmental Design (LEED) certification strategies for existing office building projects in the United States is a pressing issue requiring attention as it will help LEED professionals select the optimal certification strategy for each project. In this context, a quantitative research methodology with purposive sampling was used in this study to evaluate the impacts of project/building characteristics in LEED for Existing Buildings version 4 (LEED-EB v4) gold-certified projects in the U.S. LEED-EB v4 project/building characteristics include the project size and the number of buildings built before and after the 1973 energy crisis. LEED-EB-certified projects include a score for Location and Transportation credit (LTc1, “alternative transportation”) and scores for Energy and Atmosphere credits (EAcs) (EAc6, “renewable energy and carbon offsets”, and EAc8, “optimize energy performance”). From 112 LEED-EB v4 projects, the two following groups of projects with specific achievements were selected: Group 1 (n1 = 13), which included high achievements in LTc1 and low achievements in EAc6 and EAc8, and Group 2 (n2 = 13), which included high achievements in LTc1, EAc6, and EAc8. Exact Wilcoxon–Mann–Whitney and Fisher’s exact 2 × 2 tests were used to estimate significant differences between the two groups. The results of the selection of LEED-EB-certified projects in Groups 1 and 2 were that Group 2 outperformed Group 1 in EAc6 and EAc8 (p < 0.0001), while there was no significant difference between Groups 1 and 2 in LTc1 (p = 0.199). As a result, Group 1 outperformed Group 2 in LEED-EB v4 project size (p = 0.017). Group 2 outperformed Group 1 in the number of LEED-EB v4 gold-certified projects in buildings constructed after the 1973 US energy crisis (p = 0.005). It is concluded that, when choosing a LEED certification strategy for existing office buildings in the United States, LEED professionals should consider the 1973 energy crisis and the size of the LEED project.

1. Introduction

1.1. General Point of View

In 1987, the Brundtland Report Our Common Future defined the principle of sustainable development as “…development that meets the needs of the present without compromising the ability of future generations to meet their own needs” [1]. In particular, this principle underlies reducing operational energy (used for heating, cooling, and lighting) in buildings.
It is well known that buildings are the main source of global greenhouse gas emissions, accounting for 30–40% of all operational energy used in the world [2]; however, the problem of reducing operational energy consumption in existing buildings, particularly those built from 1915 to the present, is not trivial.
There are at least two factors that can influence the reduction in operational energy consumption in an existing building: its (1) size and (2) year of construction.
According to [3], different heating, ventilation, and air conditioning (HVAC) systems are preferable for large and small buildings: central systems (cooling towers) and decentralized systems (packaged air conditioners), respectively. According to [4], different window-to-wall ratios (WWRs) are recommended for large and small buildings, approximately 50% and 30%, respectively. Therefore, different HVAC systems and WWRs can influence primary energy consumption [5].
Oldfield et al. [6] showed that in the United States, office buildings built before the 1973 energy crisis consume significantly more operational energy than office buildings built after the crisis; for these buildings, a reduction in energy consumption was achieved through architectural innovations, such as reducing the ratio of the envelope surface area to the volume, using double glazing instead of single glazing, and using natural and mixed ventilation instead of mechanical ventilation.
However, the development of a systematic approach to solving this problem only began in the 1990s. One component of this approach is the development of Green Building Rating Systems [7]. In this study, the author focuses on the US Green Building Rating System (USGBC).

1.2. US Green Building Rating System

In 1993, the USGBC was founded for the specific purpose of creating a system of national standards in order to stimulate interest in building more sustainably [8]. In 2002, the USGBC launched the Leadership in Energy and Environmental Design of Existing Buildings (LEED-EB) system to reduce operational energy consumption in buildings through LEED certification procedures [9]. The LEED-EB system evolved from a pilot version in 2002 (1.0) to version 4 (v4) in 2013, via versions 2.0 in 2005 and 3.0 in 2009. It should be noted that LEED-EB-certified buildings must be recertified within 5 years to receive a new LEED certificate [10].
The LEED-EB v4 system contains four levels of certification: certified (40–49 points), silver (50–59 points), gold (60–79 points), and platinum (80–120 points). Increasing the certification level from certified through silver and gold to platinum in LEED-certified projects reduces buildings’ environmental impact [11].
The LEED-EB v4 system contains six main categories and two additional categories. Each category consists of one or more credits and has a different number of maximum points (max pts). The six main categories are energy and atmosphere (EA (38 max pts)), location and transportation (LT (15 max pts)), indoor environmental quality (EQ (17 max pts)), water efficiency (WE (12 max pts)), sustainable sites (SS (10 max pts)), and materials and resources (MRs (8 max pts)); the two additional categories are innovation (IN (6 max pts)) and regional priority (RP (4 max pts)).
Table 1 shows credits from two LEED-EB v4 categories: LT and EA. The LT category contains one credit (LTc1), and the EA category contains eight credits (EAc1–8).

1.3. LEED-EB Certification at the Gold Certification Level

It should be noted that in determining the LEED-EB v4 certification strategy at the gold certification level, EQ, WE, MR, and SS credits play minor roles, while LTc1, “alternative transportation” (15 max pts), EAc6, “renewable energy and carbon offsets” (5 max pts), and EAc8, “optimize energy performance” (20 max pts), credits play major roles [12]. Pushkar [12] showed that an increase in performance in EAc8 was associated with a decrease in EAc6 performance when LTc1 achieved the highest possible scores; in parallel, in EQ, WE, MR, and SS, credits were not associated with changes in EAc8 and EAc6 in LEED-EB gold-certified projects. Based on this fact, we conclude that the achievements in EQ, WE, MR, and SS scores reflect constant (baseline) levels rather than their contribution to the choice of LEED certification strategy for LEED-EB v4 gold-certified office projects. In addition, if LEED-EB v3 (the latest version at that time) gold-certified projects were located in a prime urban location (for example, New York, Chicago, or Washington, D.C.), the LEED-EB v3 “alternative commuting transportation” credit scores approached or were equal to their maximum due to easy access to alternative transportation systems [13].
Thus, in assessing the two types of LEED certification strategies based on low/high operation energy performance in buildings, it can be helpful to sort LEED-EB v4 gold-certified office projects into two groups—Group 1, i.e., projects with low performance in EAc6 and EAc8, and Group 2, i.e., projects with high performance in EAc6 and EAc8, with LTc1 demonstrating high performance in both groups. Recently, a similar approach was applied to study LEED for commercial interior version 4 (LEED-CI v4) office certification strategies at the gold certification level in Manhattan, NY, USA, and Shanghai, China [14,15]. Additionally, it was noted that the LEED certification strategy for LEED-EB v4 gold-certified office projects in the United States depends on the size of the LEED project [16].

2. Literature Review

2.1. Unexplored Factors in LEED Certification Strategy

A literature analysis found that that the impact of the LEED project size and year of construction (before or after the 1973 energy crisis) on the choice of LEED certification strategy for LEED-EB v4 office buildings has been poorly studied (regarding LEED project size) or not studied at all (regarding the 1973 energy crisis).
One possible method through which to identify the relationship between construction year and EAc6 and EAc8 performance in LEED-EB v4 gold-certified projects is to analyze actual annual energy consumption data for those projects. It should be noted that LEED is more of a design tool than a performance measurement tool, so it focuses on modeling energy use rather than actual energy consumption [17].
According to [18], the USGBC collects annual energy consumption data, particularly for LEED-EB v4 gold-certified projects in the United States; however, they note that the USGBC has not released these data publicly or published any scientific analysis of the data [18]. A review of the Web of Science and Google Scholar databases found no studies that could establish a relationship between the timing of office building construction (i.e., before or after the 1973 energy crisis) and the achievement of any version of LEED-EB credits, which are responsible for reducing the building’s operational energy consumption.

2.2. Research Gap

Only three studies were identified that analyzed the relationship between low and high EAc6 and EAc8 scores in LEED-EB v4 gold-certified office projects. A critical analysis of these studies is presented below.
In the two following studies [12,19], LEED-EB-v4 gold-certified office projects in Europe were analyzed in the following manners: (1) a comparison between Finland (Group 1, n = 14) and Spain (Group 2, n = 16) and (2) a comparison between the LEED-certified projects with the highest EAc8 scores (Group 1, n = 15) and those with the lowest EAc8 scores (Group 2, n = 15) in Spain. Both studies showed similar results in that low EAc6 scores were associated with high EAc8 scores, and vice versa. The limitations of these studies include a lack of consideration regarding the size of the LEED project and the year of building construction.
In 2021, the impact of project size on the choice of LEED-EB v4 gold certification strategy in the United States was examined for the first time [16]; at that time, there were only 26 LEED-EB v4 gold-certified projects in the USGBC database. The LEED-EB v4 data were divided into the following two groups based on LEED project size: small (median = 11,625 m2) and large (median = 49,861 m2). The small group contained 6 LEED-EB v4 gold-certified office projects and the large group contained 20; it was shown that an increase in the size of a LEED-EB v4 project is associated with decreases in EAc6 from 3.0 points (median) to 2.0 points (median) (p = 0.045), and in EAc8 from 19.5 points (median) to 16.5 points (median) (p = 0.076).
The first limitation of this study is the small overall sample size of LEED-EB v4 gold-certified office projects (n = 26); therefore, the impact of LEED-EB v4 project size on LEED certification strategy has not been sufficiently studied. The second limitation of this study is that the LEED certification strategy was not studied in the context of construction prior to or after the 1973 energy crisis.

2.3. Goal and Problem Statement

The objective of the current study was to evaluate the impact of LEED-EB v4 project size and building construction year (i.e., before or after the 1973 energy crisis) on the choice of LEED certification strategy for LEED-EB v4 gold-certified office projects in the United States.
The problem is stated below. Thus, this study examines the potential influence of LEED-EB v4 project size and office building construction date (i.e., before or after the 1973 energy crisis) on the choice of LEED certification strategy for LEED-EB v4 gold-certified office projects in the United States.
The relationship between LEED-EB v4 gold-certified office projects and the 1973 energy crisis has not yet been studied; thus, this study is the first practical example of such research in the field of sustainable green building. Analyzing the sustainability of office buildings built before the 1973 energy crisis through an analysis of LEED-EB v4 gold-certified projects will likely provide new insights into sustainable development in U.S. cities.

2.4. Innovation, Novelty, and Significance

The innovation of this study is its use of the inversion problem-solving approach (IPSA) to create a new solution for evaluating LEED-EB v4 gold-certified projects in the United States. IPSA involves the following two steps: collecting a large number of primary sampling units from the same sample frame (i.e., LEED-EB v4 gold-certified projects in the USA; total N = 112) and selecting from LEED-EB v4 gold-certified projects two small groups (n1 = n2 = 13) with radically different LEED certification strategies (i.e., Groups 1 and 2, with low/high achievements in EAc6 and EAc8, respectively). Thus, identified differences such as the size of the LEED project or whether the building was constructed before or after the 1973 energy crisis in the United States may be factors influencing the choice of LEED certification strategies.
The novelty of this study is that it is the first to identify significant differences in LEED energy efficiency certification strategies among LEED-EB v4 gold-certified office projects in buildings constructed before or after the 1973 U.S. energy crisis.
The significance of this study is that its findings will help LEED practitioners use the knowledge of whether a given building was built before or after the 1973 energy crisis, as well as the size of the LEED-EB v4 gold-certified project in a given building, to determine a sustainable LEED energy efficiency certification strategy.
It should be noted that the sample size (total N = 112) is equivalent to the number of US-LEED-EB v4 gold-certified office projects that were available in the USGBC database as of 28 August 2024 (http://www.gbig.org (accessed on 28 August 2024)). The sample size in both groups (n1 = n2 = 13) is acceptable for obtaining a reliable statistical conclusion.

3. Materials and Methods

3.1. Study Design

LEED data were collected from one country (U.S.), one LEED system (LEED-EB), one version (v4), one certification level (gold), and one space type (office); this design minimizes the influence of uncontrollable factors [20,21]. It has been previously shown that different countries, LEED systems, versions, certification levels, and space types use different LEED certification strategies (e.g., [22,23,24,25]).
In the current study, an inversion problem-solving approach was used to identify the causal factors leading to different LEED-EB v4 certification strategies. The author selected two small groups (n1 = n2 = 13) from one large group (n = 112), wherein Group 1 included LEED EB v4-certified projects with high LTc1 and low EAc6 and EAc8 scores, while Group 2 included LEED-EB v4-certified projects with high LTc1, EAc6, and EAc8 scores. The LEED project size and the year the LEED-certified building was built, i.e., before or after the 1973 energy crisis, were then compared between Groups 1 and 2 to determine whether these two variables impacted LTc1, EAc6, EAc8, and overall LEED-EB v4 achievement in LEED-EB v4-certified projects.
Of the 112 office projects that achieved LEED-EB v4 gold certification, their assortment into four groups (n1 = 13, n2 = 13, n3 = 12, and n4 = 12, respectively) was based on a specific combination of achievements in three key credits: LTc1, EAc6, and EAc8. The remaining LEED-EB v4 gold-certified office projects did not meet the specific combination of achievements of these three key credits and were therefore not included in any of the four groups. In this study, achievement of three key scores, namely LTc1, EAc6, and EAc8 in LEED-EB v4 gold-certified office projects, is a result of both the location and diversity of office building types. The LTc1 score indicates advances in alternative transport and its infrastructure, while the EAc6 and EAc8 scores indicate advances in operational energy efficiency in office buildings.
This study employs the following steps: (1) Data from a total of 216 LEED-EB v4-certified office projects (n = 216) in the United States were collected. (2) These LEED-certified projects were sorted into the four following LEED certification levels: platinum (n = 24), gold (n = 112), silver (n = 46), and certified (n = 34). (3) LEED-EB v4 platinum, silver, and certified projects were excluded from the study due to their small sample sizes. (4) The 112 LEED-EB v4 gold-certified office projects were sorted into four groups—designated as Groups 1, 2, 3, and 4—according to requirements for each group. (5) Groups 1 (n = 13) and 2 (n = 13) were significantly different from each other, while Groups 3 (n = 12) and 4 (n = 12) were slightly different from each other and together occupied an intermediate position between Groups 1 and 2. (6) Groups 3 and 4 were excluded from subsequent study, while Groups 1 and 2 were studied further.

3.2. Data Collection

Figure 1 displays a flowchart of the collection process and sample sizes of LEED-EB v4-certified office projects in the US.
The USGBC and Green Building Information Gateway (GBIG) databases were used to identify 216 LEED-EB v4-certified office space projects in the United States (on 13 July 2024) [26,27]. The USGBC database was used to collect LEED-EB v4 scores, while the GBIG database was used to determine whether LEED-EB v4-certified projects were office buildings and the year of construction of buildings in LEED-EB v4 gold-certified office projects using the Energy Star protocol.
The next step was to sort the LEED-EB v4 projects into four certification levels—platinum (n = 24), gold (n = 112), silver (n = 46), and certified (n = 34)—a distinction which was necessary because each certification level has its own unique set of LEED certification strategies. Combining the four certification groups into one group would therefore result in a misleading description of the LEED certification strategy. Consequently, in order to achieve the objective of this study, the author focused only on LEED-EB v4 gold-certified office projects, since other certification levels contained small numbers of projects.

3.3. LEED-EB v4 Gold-Certified Data Sorting

The primary selection criteria for the 112 LEED-EB v4 gold-certified office projects into two groups included (i) low (i.e., Group 1, n1 = 13) or high (i.e., Group 2, n2 = 13) scores in two key credits, demonstrating the low or high energy efficiency of the office building, respectively; and (ii) high LTc1 scores, demonstrating accessibility to alternative transportation from office buildings in both Groups 1 and 2.
The author applied low-/moderate-/high-valued logic to the percentage of average score (PAS) results as the ratio of achieved points to maximum points [28] for LTc1, EAc6, and EAc8 in order to sort the three types of LEED-EB v4 certification strategies. Table 2 shows the boundaries of the three performance levels—low, moderate and high—for LTc1, EAc6, and EAc8.
Figure 2 shows that Groups 1 and 2 are fundamentally different from each other, while Groups 3 and 4 together occupy an intermediate position between Groups 1 and 2.
An analysis of Figure 2 shows that between Groups 1 and 2, the largest differences are present in the performance of two key credits, EAc6 and EAc8, which represent the reduction in environmental damage from a building’s operational energy consumption. For EAc6 and EAc8, Group 1 showed low performance, while Group 2 showed high performance; both groups showed high performance for LTc1. Groups 3 and 4 differed fundamentally from each other by only one credit: EAc6. Group 3 showed low performance for EAc6, while Group 4 showed high performance for EAc6. It should be noted that Groups 3 and 4 together occupy an intermediate position in terms of the degree of differences between Groups 1 and 2. Therefore, the author of this study focused only on a comparative analysis between Groups 1 and 2.
Groups 1 and 2 each contain 13 LEED-EB v4 gold-certified office building projects with the following inputs: LEED-EB v4 project size, year of construction, and scores for the three key LEED-EB v4 credits, LTc1, EAc6, and EAc8 (Appendix A, Table A1 and Table A2).
Exact Wilcoxon–Mann–Whitney (WMW) and Fisher’s exact 2 × 2 tests were used to estimate significant differences between Groups 1 and 2 in terms of LEED-EB v4 scores, LEED-EB v4 project sizes, and the construction years of LEED-EB v4 buildings.
Instead of the Student’s t-test, the exact WMW was used because the normality assumption of the LEED data was not met [14]. Instead of the approximate WMW, the exact WMW was used for two reasons: (1) the sample size was small and (2) the LEED data contained a certain amount of “tied data” [29]. Fisher’s exact 2 × 2 test was used to assess the significant difference on a binary scale between buildings built before (i.e., Group 1) or after (i.e., Group 2) the 1973 energy crisis.

3.4. Statistical Analysis

The LTc1, EAc6, and EAc8 scores were discrete interval variables with relatively small numbers of values, non-normal distributions, and sample sizes for two groups, n1 = n2 = 13; in this context, the nonparametric exact WMW rank test was used instead of the parametric t-test. The WMW rank sum test statistics and two-sided p-values from the exact WMW test are presented in tabular form (Appendix A, Table A3). The WMW test does not have degrees of freedom associated with the sampling distribution, as is the case with distribution-based tests such as the t-test, F-test, or chi-square test. The corresponding determination of critical values is carried out via an exact listing of all possible sets of differences in estimates. As the factor of buildings built before or after the 1973 energy crisis was presented as a binary response and the sample sizes of the two groups were small (i.e., n1 = n2 = 13), Fisher’s exact test, using a 2 × 2 table with Lancaster correction, was used instead of the chi-square test.
When the LEED scores and project sizes were presented on ordinal or interval scales, the exact WMW rank test [29] and Cliff’s δ nonparametric effect size analysis [30] were used to compare differences between the two groups. Although the LEED data contained tied observations, in their original study, Bergmann et al. [29] showed that if the sample size was n1 = n2 ≥ 12, the exact WMW procedure was acceptable.
Since building construction years were presented on a binary scale (before and after the 1973 energy crisis), Fisher’s exact test using a 2 × 2 table with Lancaster’s correction [31] and the natural logarithm of the odds ratio (lnθ) (i.e., the effect size test) [32] were used to compare differences between the two groups; because buildings take several years to construct, buildings built only after 1980 were counted as “built after the 1973 energy crisis”. According to [31], the minimum sample for Fisher’s exact test, using a 2 × 2 table with Lancaster’s correction, is n1 = n2 = 3.

3.5. Effect Size and p-Value Interpretations

In both δ and lnθ, (+) indicates that Group 1 outperformed Group 2, (−) indicates that Group 2 outperformed Group 1, and zero indicates no difference between the groups’ Cliff’s δ effect size ranges between −1 and +1 [30]. lnθ ranges from minus infinity to plus infinity [32]; it is considered (1) negligible if |δ| < 0.147, (2) small if 0.147 ≤ |δ| < 0.33, (3) medium if 0.33 ≤ |δ| < 0.474, and (4) large if |δ| ≥ 0.474 [33]. The lnθ effect size is considered (1) negligible if |δ| < 0.51, (2) small if 0.51 ≤ |δ| < 1.24, (3) medium if 1.24 ≤ |δ| < 1.90, and (4) large if |δ| ≥ 1.90 [34].
Three-valued logic was used to interpret two-sided p-values as follows: either there is a difference between the two groups, there is no difference between the two groups, or judgment regarding the difference between the groups is suspended [35,36].

4. Results and Discussion

This section includes a three-step analysis. Descriptive and inferential statistics are used in all three steps. The first step includes selected scores for the three LEED credits (i.e., LTc1, EAc6, and EAc8) and overall LEED credit scores. The second step includes an analysis of LEED project size. The third step includes a number of LEED-EB v4 gold-certified office projects in buildings constructed before or after the 1973 energy crisis.

4.1. Comparison of Two Sorted Groups

Table 3 shows a comparative analysis of Groups 1 and 2 across the three key LEED-EB v4 credits.
LTc1, alternative transportation, requires the use of public transportation, such as buses, subways, ridesharing, and green vehicles, over conventional cars [37], for which no significant difference was found between Groups 1 and 2 (p = 0.199). Projects in both groups are being implemented in New York, Chicago, Washington D.C., Los Angeles, Denver, Boston, and San Jose (Appendix A, Table A1 and Table A2), cities with developed urban environments and considerable accessibility to public transportation; therefore, it is not surprising that both groups had similarly high LTc1 achievements.
EAc6, renewable energy and carbon offsets, requires that part of a building’s operational energy be produced using renewable energy sources, such as solar panels and wind turbines, or through a green energy purchase contract [37]. EAc8, optimize energy performance, requires a building’s energy consumption to be reduced by 26–45% compared to the national average [37]. As shown in Table 3, Group 2 outperformed Group 1 in both EAc6 and EAc8 (p < 0.001). If a LEED-EB v4 gold-certified office project achieves low scores in EAc6 and EAc8 and high scores in LTc1, the overall LEED-EB v4 score meets the minimum requirements for gold certification (Group 1); if a LEED-EB v4 gold-certified office project achieves high scores in EAc6, EAc8, and LTc1, the overall LEED-EB v4 score exceeds the minimum score for gold certification by 11.7% and can therefore achieve the platinum level upon recertification (Group 2).
While LEED-EB v4 gold-certified projects (minimum 60 points) demonstrate near-maximum or maximum LT achievements (14–15 points, respectively), different LEED certification strategies can be achieved through different achievements in EAc6 (range: 0–5 points) and EAc8 (range: 0–20 points). Different achievements in EAc6 and EAc8 in LEED-EB v4 gold standard certified projects may depend on the architectural and/or structural properties of the existing U.S. office buildings.
A statistical difference between Group 1 and Group 2 at the LEED-EB v4 categorical level showed that Group 2 outperformed Group 1 in the EA category (median delta = 14 points, p < 0.001, Appendix A, Table A4). It is possible that achievements in the remaining LEED categories (i.e., SS, WE, MR, and EQ) reflect the LEED professionals’ drive to achieve LEED Gold certification (i.e., the “Point Chasing Mentality” principle) more than the influence of the architectural and construction properties of the buildings on the choice of LEED certification strategy.
The factors (the sizes of LEED-EB v4 gold-certified projects and their construction years) that influenced the differences in the EAc6 and EAc8 scores between the two groups are analyzed below.

4.2. Factors Affecting Differences in Energy Credits

4.2.1. LEED-EB v4 Project Sizes

Table 4 shows that Group 1 outperformed Group 2 in LEED-EB v4 project size (p = 0.017).
The size of the LEED-EB v4 project from Group 1 is almost three times the size of the LEED-EB v4 project from Group 2 (p = 0.017); thus, it can be confirmed that decreased project size results in differences between Group 1 (low EAc6 and EAc8 scores) and Group 2 (high EAc6 and EAc8 scores). In terms of EAc6, renewable energy and carbon offsetting, it can be assumed that this credit may be more effective in smaller buildings than in larger ones because, for example, compared to larger buildings, smaller buildings have a higher roof-to-building size ratio, making solar panels more suitable for small buildings than for large ones. In terms of EAc8, optimize energy performance, as explained earlier, larger buildings use central HVAC systems (boilers and chillers to heat and cool the air, respectively), while smaller buildings use decentralized HVAC systems (stand-alone packaged air conditioners) to heat and cool the air [3]. Decentralized HVAC systems are more flexible in regulating energy consumption for different offices, while centralized systems do not have this ability and supply all offices with the same energy density; thus, smaller buildings have more opportunities to optimize energy consumption than larger buildings [16], which may help explain why the Group 2 LEED-EB-certified projects were more energy efficient than the Group 1 LEED-EB-certified projects, as shown in Table 3.

4.2.2. LEED-EB v4 Project Construction Years

As shown in Figure 3, the results of Fisher’s exact test using 2 × 2 tables show a significant difference, with a large effect size for the buildings built before 1973/buildings built after 1980 ratio between Groups 1 and 2 (p = 0.005; lnθ = 2.52).
Thus, for LEED-EB v4 gold-certified office projects, low EAc6 and EAc8 scores are associated with buildings built before the 1973 energy crisis, while high EAc6 and EAc8 scores are associated with buildings built after the 1973 energy crisis; in other words, in Group 1, buildings built before 1973 outnumber buildings built after 1980, while, in Group 2, buildings built after 1980 outnumber buildings built before 1973.
The higher energy efficiency of Group 2 projects can be explained by taking into account the energy standard that emerged as a result of the 1973 energy crisis; in this respect, the United States Department of Energy was created in accordance with the recommendations of the Energy Policy and Conservation Act of 1975 [38,39] and the Energy Policy Act of 1992 [40,41]. At the federal level, the United States Department of Energy has developed the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) voluntary energy codes for commercial and residential buildings [42]. At the same time, many states have introduced their own rules and regulations regarding energy consumption in buildings; the first building energy efficiency standards were adopted in California in 1978, after which energy regulations were then issued in other states, including Arizona, Georgia, Illinois, Iowa, Massachusetts, and New York [43].
Energy savings depend largely on the following parameters: the orientation of the building, the ratio of windows to walls (the “transparency” of the facade), the type of glazing, and the thermal mass of the wall and its insulation [44]. In buildings constructed before the 1973 energy crisis, these parameters were often designed with architectural and aesthetic characteristics in mind rather than energy efficiency; the problem is that some parameters, such as the orientation of the building and the transparency of the facade, cannot be changed even when reconstructing an existing building [5]. It should be noted that the trade-off between building architecture and reducing building operational energy is a key issue in modern building design [45].
Therefore, it may be supposed that due to the emerging standardization of energy consumption, offices built after the 1973 energy crisis are more energy-efficient than those built before the 1973 energy crisis, a possible additional reason why Group 2 projects were more energy-efficient than Group 1 projects (Table 3).
The energy crisis of 1973 radically changed the approach to the construction of new large office buildings, as well as the maintenance of large office buildings built before 1973. In this context, the three following main directions have emerged: (i) the development of energy-saving technologies, with a gradual replacement of non-renewable energy sources with renewable ones at the country level [46]; (ii) the use of materials with lower thermal conductivity in building envelopes [47]; and (iii) a reduction in the operational energy of the building throughout its entire life cycle [17].
In the present study, the EAc6, “renewable energy and carbon offsets”, and EAc8, “optimize energy performance”, scores of LEED-EB v4 gold-certified office projects were analyzed; these two credits are directly related to the building’s operational energy, but the sources of the primary energy values for LEED-EB v4 gold-certified projects are not publicly available [18]. As a result, EAc6 and EAc8 scores cannot currently be converted into a life cycle assessment [48], and the results obtained cannot currently be interpreted using other methods.
However, a comparison of Groups 1 and 2 allows us to state with a high degree of certainty that Group 1 outperforms Group 2 in terms of LEED-EB v4 project size, as well as that LEED-EB v4 gold-certified buildings built before 1973 achieve low EAc6 and EAc8 scores while LEED-EB v4 gold-certified buildings built after 1973 achieve high EAc6 and EAc8 scores, an outcome which can be explained by the fact that the architectural features of buildings built before 1973 did not allow LEED-EB v4 professionals to achieve high scores in EAc6 and EAc8 in LEED-EB v4 gold-certified projects. The Web of Science and Google Scholar databases do not describe this fact.

5. Conclusions

This study produced some unanticipated results: after twenty-three years of using the LEED-EB system (the LEED-EB system was launched in 2002 [9]), the challenge of improving the operational energy efficiency of existing office buildings in the United States remains unresolved. Increasing LEED project size is associated with decreasing operational energy efficiency in buildings, contradicting the statement that LEED is a “one-size-fits-all” assessment tool that can be used to assess buildings of every size, from small office buildings to skyscrapers [49].
An inversion problem approach was used to analyze two fundamentally different types of LEED certification strategies for LEED-EB v4 gold-certified projects in the United States: (1) a high score in LTc1 and low scores in EAc6 and EAc8, i.e., Group 1, and (2) high scores in LTc1, EAc6, and EAc8, i.e., Group 2.
The comparative analysis showed that Group 1 outperformed Group 2 in the size of LEED-EB projects (p = 0.017), while Group 2 outperformed Group 1 in the number of office buildings constructed since the 1973 US energy crisis (p = 0.005).
Thus, there are at least two factors acting in parallel that influence potential energy saving limitations in LEED-EB v4 gold-certified projects, namely (i) the increase in project size (median) from 15,922 m2 to 45,782 m2 and (ii) whether the building was constructed before or after the 1973 energy crisis.

6. Limitations

Many statistical conclusions regarding the energy performance of LEED-certified projects may be misleading due to reporting and selection biases. Reporting bias may arise from selective disclosure or omission of energy efficiency information in LEED-certified projects, e.g., certain projects may inflate their energy performance or LEED credit scores; selection bias arises from the fact that certain types of LEED-certified projects are more likely to be included in the USGBC and GBIG databases. Both may affect the reliability of this study’s results.
To minimize the impact of reporting and selection biases on statistical inferences, the following study design was adopted: (i) LEED-EB v4 gold-certified projects in the United States were collected (n = 112), and (ii) from 112 US LEED-EB v4 gold-certified office projects, two small groups were selected, in which Group 1 included 13 US-LEED-EB v4 gold-certified office projects with low scores in EAc6 and EAc8 and high scores in LTc1, and Group 2 included 13 US-LEED-EB v4 gold-certified office projects with high scores in EAc6, EAc8, and in LTc1. The author focused on two fundamentally different small groups, in which the variables are only two key LEED indicators, in order to use simple significance tests to draw statistical inferences; consequently, a limitation of this study design is that only two small groups were compared (n1 = 13, n2 = 13).
Recently, the structural decomposition method (DSD) has been used to process big data with many variables (e.g., economic efficiency, emission factor, energy intensity, gross domestic product per capita, industrial structure, and population density) over time. The DSD method can be used to estimate the global commercial operation of buildings [50] or the global carbon transition in the passenger transportation sector [51]. Using the DSD approach avoids biased research results by including the socio-economic characteristics of workers in all LEED gold-certified office buildings in the United States.
One limitation of the current study is the lack of direct measurement of the energy consumption of LEED-EB gold-certified office projects. According to Scofield et al. [18], the USGBC does not make these data publicly available. However, measuring the actual operational energy consumption (i.e., heating, cooling, and lighting consumption) in LEED-EB-certified buildings provides an accurate LEED-EB system score.

7. Future Research

The results obtained in this study may shed light on how to use the LEED-EB system to improve the energy efficiency of historic or heritage buildings. According to ELDib [52], LEED-EB emphasizes operational energy improvements rather than major renovations, allowing historic or heritage buildings to remain functional and efficient. This makes the LEED-EB system, through “adaptive reuse”, particularly valuable for protecting historic properties both in the United States and around the world [52].

Funding

This research received no external funding.

Data Availability Statement

Data are contained within the article.

Acknowledgments

The author would like to thank the architect David Knafo for his moral and scientific support in this research.

Conflicts of Interest

The authors declare no conflict of interest.

Appendix A

Table A1. Group 1: US-LEED-EB v4 gold-certified office projects with high LTc1 and low EAc6, and EAc8 performance with a Percentage Average Score (PAS).
Table A1. Group 1: US-LEED-EB v4 gold-certified office projects with high LTc1 and low EAc6, and EAc8 performance with a Percentage Average Score (PAS).
AddressProject NameCertification DateYear ConstructedLTc1 (PAS)EAc6 (PAS)EAc8 (PAS)
655 3rd Ave, New York, NY 10017, USA655 Third Avenue9 July 20191958 115 (100)2 (40)7 (35)
675 3rd Avenue, New York, NY 10017, USA675 Third Avenue and 205 East 42nd Street16 September 2019196615 (100)2 (40)4 (20)
231 S. LaSalle Street, Chicago, IL 60604, USA231 South LaSalle31 July 2023192415 (100)0 (0)9 (45)
485 Lexington Avenue, New York, NY 10017, USA485 Lexington Avenue Recertification14 January 2019195815 (100)0 (0)6 (30)
114 West 47th Street, New York, NY 10036, USA114 W47th St—Recert23 June 2022198915 (100)0 (0)6 (30)
1133 15th Street NW, Washington, DC 20005, USA1133 15th Street Recertification17 January 2024196915 (100)0 (0)0 (0)
330 North Wabash Avenue, Chicago, IL 60611, USA330 North Wabash Avenue22 May 2019197115 (100)0 (0)9 (45)
1133 Connecticut Ave NW, Washington, DC 20036, USA1133 Connecticut Ave6 June 2022198915 (100)0 (0)8 (40)
617 W 7th Street, Los Angeles, CA 90017, USA617 W 7th St19 December 2023192315 (100)0 (0)7 (35)
523 West 6th Street, Los Angeles, CA 90014, USAPacMutual Building Recertification21 January 2020192113 (87)0 (0)9 (45)
6350 Walker Lane, Alexandria, VA 22310, USAMetro Park 27 September 2021200011 (73)0 (0)8 (40)
1200 17th Street, Denver, CO 80202, USATabor Center28 October 2021198511 (73)0 (0)7 (35)
2550 South Clark Street, Arlington, VA 22202, USAPresidential Tower12 January 2021197015 (100)0 (0)11 (55)
1 https://www.durst.org/properties/655-third-avenue (accessed on 28 November 2024).
Table A2. Group 2: US-LEED-EB v4 gold-certified office projects with high LTc1, EAc6, and EAc8 performance scores and Percentage Average Scores (PASs).
Table A2. Group 2: US-LEED-EB v4 gold-certified office projects with high LTc1, EAc6, and EAc8 performance scores and Percentage Average Scores (PASs).
AddressProject NameCertification DateYear ConstructedLTc1 (PAS)EAc6 (PAS)EAc8 (PAS)
University of California, Santa Barbara, CA 93106, USAUCSB Student Resource Building21 March 20162007 215 (100)5 (100)18 (90)
741 Technology Dr, San Jose, CA 95110, USAConcourse V—1741 Technology8 September 2022199915 (100)4 (80)20 (100)
197 Clarendon Street, Boston, MA 02116, USABerkeley/Clarendon 17 July 20181922 315 (100)4 (80)20 (100)
535 Boylston Street, Boston, MA 02116, USA535 Boylston v4 EB3 October 2018196315 (100)4 (80)20 (100)
121 Spear Street, San Francisco, CA 94105, USARincon Center Recertification30 March 2022198815 (100)3 (60)18 (90)
114 W 47th St, New York, NY 10036, USA114 W47th St3 April 2017198915 (100)3 (60)18 (90)
1220 Howell St., Seattle, WA 98101, USAMet Park North23 January 2020200014 (93)3 (60)20 (90)
2033 Gateway Place, San Jose, CA 95110, USA2033 Gateway Place3 January 2020198813 (86)3 (60)20 (100)
4101 Reservoir Road, Washington, DC 20007, USAFrench embassy10 March 2018198312 (80)3 (60)19 (95)
2001 Gateway Place, San Jose, CA 95110, USA2001 Gateway Place3 January 2020198112 (80)3 (60)20 (100)
201 Redwood Shores Parkway, Redwood City, CA 94065, USATowers At Shore Center14 October 2019200012 (80)3 (60)19 (95)
2077 Gateway Place, San Jose, CA 95110, USA2077 Gateway Place3 January 2020198411 (73)3 (60)20 (100)
2099 Gateway Place, San Jose, CA 95110, USA2099 Gateway Place3 January 2020198511 (73)3 (60)20 (100)
2 https://srb.sa.ucsb.edu/about (accessed on 28 November 2024); 3 https://www.energystar.gov/buildings/certified_buildings_and_plants/b_1075946 (accessed on 28 November 2024).
Table A3. Three key LEED credits in LEED-EB v4 gold-certified office projects in the United States. The rank sum test statistic: Group 1 (n1 = 13) vs. Group 2 (n2 = 13).
Table A3. Three key LEED credits in LEED-EB v4 gold-certified office projects in the United States. The rank sum test statistic: Group 1 (n1 = 13) vs. Group 2 (n2 = 13).
LEED-EB v4 Credit The Rank Sum Test Statisticp-Value
LTc1: alternative transportation198.50.199
EAc6: renewable energy and carbon offsets91.0<0.001
EAc8: optimize energy performance91.0<0.001
LEED-EB v4 total101.0<0.001
Table A4. Six key LEED Categories in LEED-EB v4 Gold Certified Office Projects in the United States.
Table A4. Six key LEED Categories in LEED-EB v4 Gold Certified Office Projects in the United States.
LEED-EB v4 Category (Max Points)Median, 25–75th Percentilesp-Value (Cliff’s δ)
Group 1 (n1 = 13)Group 2 (n2 = 13)
LT: location and transportation (15)15.0, 14.5–15.014.0, 12.0–15.00.199 (0.27)
SS: Sustainable sites (10)3.0, 2.8–4.53.0, 1.0–4.00.176 (0.30)
WE: Water efficiency (12)9.0, 9.0–9.26.0, 5.0–8.00.003 (0.65)
EA: energy and atmosphere (38)13.0, 12.0–15.327.0, 26.5–28.0<0.001 (−1.00)
MRs: Materials and resources (8)3.0, 2.8–5.02.0, 1.0–4.00.054 (0.44)
EQ: Indoor environmental quality (17)10.0, 7.8–11.07.0, 6.0–9.20.098 (0.38)

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Buildings 15 01080 g001
Figure 1. Flowchart of collection and sample sizes of LEED-EB v4-certified projects in the US.
Figure 1. Flowchart of collection and sample sizes of LEED-EB v4-certified projects in the US.
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Figure 2. Flowchart of sorting LEED-EB v4-certified projects into four groups according to LTc1, EAc6, and EAc8 using low-/moderate-/high-valued logic.
Figure 2. Flowchart of sorting LEED-EB v4-certified projects into four groups according to LTc1, EAc6, and EAc8 using low-/moderate-/high-valued logic.
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Figure 3. The relationship between two LEED-EB v4 energy efficiency strategies (i.e., Groups 1 and 2) in existing office buildings and buildings constructed before and after the 1973 energy crisis in the United States.
Figure 3. The relationship between two LEED-EB v4 energy efficiency strategies (i.e., Groups 1 and 2) in existing office buildings and buildings constructed before and after the 1973 energy crisis in the United States.
Buildings 15 01080 g003
Table 1. The LEED-EB v4: location and transportation credit (LTc1) and energy and atmosphere credits (EAc1–8).
Table 1. The LEED-EB v4: location and transportation credit (LTc1) and energy and atmosphere credits (EAc1–8).
LEED-EB v4 CreditMaximum Points
LTc1: alternative transportation15
EAc1: existing building commissioning—analysis2
EAc2: existing building commissioning—implementation2
EAc3: ongoing commissioning3
EAc4: advanced energy metering2
EAc5: demand response3
EAc6: renewable energy and carbon offsets5
EAc7: enhanced refrigerant management1
EAc8: optimize energy performance20
EAc1, EAc6, and EAc8 showed the highest possible scores compared to other credits. Thus, LTc1, EAc6, and EAc8 credits may have more influence than other credits when determining the LEED certification strategy for LEED-EB v4-certified projects.
Table 2. The percentage of average score (PAS) values for LTc1, EAc6, and EAc8 using low-/moderate-/high-valued logic.
Table 2. The percentage of average score (PAS) values for LTc1, EAc6, and EAc8 using low-/moderate-/high-valued logic.
LEED-EB v4 CreditMax PointsLowModerateHigh
LTc1: alternative transportation150–3940–6768–100
EAc6: renewable energy and carbon offsets50–4041–5960–100
EAc8: optimize energy performance200–5556–8990–100
Table 3. Three key LEED credits in LEED-EB v4 gold-certified office projects in the United States.
Table 3. Three key LEED credits in LEED-EB v4 gold-certified office projects in the United States.
LEED-EB v4 Credit (Max Points)Median, 25–75th Percentilesp-Value (Cliff’s δ)
Group 1 (n1 = 13)Group 2 (n2 = 13)
LTc1: alternative transportation (15)15.0, 14.5–15.014.0, 12.0–15.00.199 (0.27)
EAc6: renewable energy and carbon offsets (5)0.0, 0.0–0.03.0, 3.0–4.0<0.001 (−1.00)
EAc8: optimize energy performance (20)7.0, 6.0–9.020.0, 18.8–20.0<0.001 (−1.00)
LEED-EB v4 total 160.0, 60.0–61.067.0, 62.0–68.3<0.001 (−0.88)
1 the minimum score to achieve LEED-EB v4 gold certification for a project is 60.
Table 4. Size of LEED-EB v4 gold-certified office projects in the United States.
Table 4. Size of LEED-EB v4 gold-certified office projects in the United States.
VariableMedian, 25–75th Percentilesp-Value (Cliff’s δ)
Group 1 (n1 = 13)Group 2 (n2 = 13)
Project size (m2)45,782, 21,225–73,64415,922, 11,153–36,7190.017 (0.54)
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Pushkar, S. Leadership in Energy and Environmental Design for LEED Version 4 (LEED-EB v4) Gold Certification Strategies for Existing Buildings in the United States: A Case Study. Buildings 2025, 15, 1080. https://doi.org/10.3390/buildings15071080

AMA Style

Pushkar S. Leadership in Energy and Environmental Design for LEED Version 4 (LEED-EB v4) Gold Certification Strategies for Existing Buildings in the United States: A Case Study. Buildings. 2025; 15(7):1080. https://doi.org/10.3390/buildings15071080

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Pushkar, Svetlana. 2025. "Leadership in Energy and Environmental Design for LEED Version 4 (LEED-EB v4) Gold Certification Strategies for Existing Buildings in the United States: A Case Study" Buildings 15, no. 7: 1080. https://doi.org/10.3390/buildings15071080

APA Style

Pushkar, S. (2025). Leadership in Energy and Environmental Design for LEED Version 4 (LEED-EB v4) Gold Certification Strategies for Existing Buildings in the United States: A Case Study. Buildings, 15(7), 1080. https://doi.org/10.3390/buildings15071080

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