1. Introduction
The concrete industry is currently the largest consumer of natural resources and energy and is a huge producer of solid waste and greenhouse gas emissions. In particular, according to the United Nations Environment Program for Sustainable Buildings and Construction [
1], buildings consume 40% of energy worldwide and produce 40% of the world’s solid waste and 30% of global greenhouse gas emissions. To decrease the harmful influence of buildings on the environment, the common worldwide approach is implementing building certification under green rating systems.
The Building Research Establishment Environmental Assessment Method (BREEAM) [
2], the Assessment System for Built Environment Efficiency (CASBEE) [
3], Green Star [
4], and Leadership in Energy and Environmental Design (LEED) [
5], in addition to others, have been established in the United Kingdom, Japan, Australia, and the United States, respectively. The systems include similar environmental categories, such as energy, water, material, management, health and well-being, and transport, and each of these categories have one or several credits with deterministic performance requirements. When a project team considers credit requirements, projects receive one or several points depending on weight (importance) of this credit. According to the total sum of the awarded points, a project receives an appropriate certification level. The systems, however, face similar concerns regarding categories and credits: (1) category-related environmental issues are emphasized so social and economic issues are almost completely ignored, (2) the suggested deterministic credit-related scoring ignores uncertainty in value judgments about credit performance, and (3) credit-related weighting is not well supported with no consensus on how credit importance should be derived [
6].
LEED is the most recognized rating system, applied not only in the United States but also internationally [
7]. LEED was established by the U.S. Green Building Council (USGBC), which is a private sector organization. The abovementioned early green rating system-related concerns are also relevant to LEED. In applying the triple bottom line, which emprises environmental, social, and economic sustainability, LEED emphasizes the environmental aspect (83% of all the credits are environmentally-related), thereby ignoring economic and social issues, as only 1% and 16% of all the credits are economic- and social-related, respectively [
8]. When applying weights to the credits, LEED places more importance on active energy design through installation of energy-efficient heating, ventilation, and air conditioning (HVAC) systems (82% of all the possible points in the energy category) and less on passive energy design through use of bio-climatic and passive solar aspects in building design (18% of all the possible points in the energy category) [
9].
New versions LEED and the other rating systems are being constantly developed and improved. In 1998, the USGBC launched LEED v1.0 for new construction buildings (LEED-NC). Additional versions were introduced: LEED-NCv2.0 in 2001, LEED-NCv2.2 in 2005, LEED-NCv3 in 2009, and LEED-NCv4 in 2013. Although other LEED rating systems exist for Existing Buildings: Operations and Maintenance (LEED-EB), Commercial Interiors (LEED-CI), and Core and Shell Development (LEED-C & S), LEED-NC is still one of the most requested [
10]. To promote continuous LEED improvement in future versions, empirical studies analyzing building projects certified under the current LEED version appear necessary. Such studies can reveal the more successful LEED requirements that are willingly applied by project teams and the less successful requirements that have been less adopted.
In LEED-NCv2.2 [
11], the total number of available points was 69 and all credits had the same weighting (1 possible point). To receive Certified, Silver, Gold, or Platinum certification, LEED-NCv2.2-certified projects were required to achieve a total 26–32, 33–38, 39–51, or 52–69 points, respectively [
8]. The LEED-NCv2.2 categories were: Sustainable Sites (SS), with 14 possible points; Water Efficiency (WE), with five possible points; Energy and Atmosphere (EA), with 17 possible points; Materials and Resources (MR), with 13 possible points; Indoor Environmental Quality (EQ), with 15 possible points; and Innovation and Design Process (IN), with 5 possible points. The projects certified under this version were studied by Fuerst [
12] and Wu et al. [
13].
Fuerst [
12] analyzed over 2000 LEED-NC, LEED-CI, LEED-C & S, and LEED-EB certified projects registered as of March 2009 in the U.S. The analyzed LEED versions were not reported by Fuerst [
9]. However, according to the publishing date of this study, versions 1–2.2 were likely considered. Fuerst [
12] only reported the achievements of the total number of LEED points (i.e., certification achievements), claiming that these were low. In particular, most of the projects received certification with a total number of points only slightly above the bottom thresholds for each certification level (26, 33, 39, and 52 for Certified, Silver, Gold, and Platinum, respectively).
Wu et al. [
13] analyzed the category achievement of 5340 LEEDv2.2 projects around the world including the U.S., reporting varied achievements. In particular, the analysis of all projects together demonstrated that the IN category achievement was high (80.1% of possible points), the SS, WE, and EQ category achievements were intermediate (57.3–68.9% of possible points), and the EA and MR category achievements were low (42.6–43.4% of possible points). A comparison between two adjacent certification levels (Silver vs. Certified, Gold vs. Silver, and Platinum vs. Gold), i.e., cross-certification analysis, revealed that from level to level, EA category achievement increased considerably, SS and EQ category achievements showed intermediate increases, and WE, MR, and IN category achievements showed low increases.
The next version, LEED-NCv3 [
14], was reshaped to include 110 points in total. As a consequence, the available points became 26, 10, 35, 14, 15, and 6 for SS, WE, EA, MR, EQ, and IN categories, respectively. Thus, the EA category, which had low achievements in projects certified under the previous LEED-NCv2.2 [
13], was enhanced in LEED-NCv3, suggesting 19 possible points instead of the previous 10. However, the MR category, which also had low achievements in projects certified under LEED-NCv2.2 [
13], remained the same as in the previous version. Different weights were applied to the different credits. For example, in the SS category, the Alternative transportation–public transportation access credit included six possible points, whereas Alternative transportation–low-emitting and fuel-efficient vehicles had four possible points. A new category, Regional Priority (RP) credit, with four bonus points, was first introduced in LEEDv3 [
14] to encourage solving U.S. regional environmental issues.
The certification and category analysis of projects certified under LEED-NCv3 were extensively studied by Wu, et al. [
15] and Pushkar and Verbitsky [
16,
17]. Wu, et al. [
15] studied 3416 LEED-NCv3 certified projects worldwide, including the U.S. The analysis of all projects together demonstrated that the SS, WE, EQ, and IN category achievements were intermediate (59.1–69.8% of possible points), and the EA and MR category achievements were low (40.3% and 38.7% of possible points). The cross-certification analysis of LEED-NCv3-certified projects confirmed the results previously reported by Wu et al. [
13] for projects certified under LEED-NCv2.2. In particular, from level to level, EA category achievement showed considerable increases, the SS and EQ category achievements showed intermediate increases, and the WE, MR, and IN category achievements showed low increases.
Pushkar and Verbitsky [
16] studied 920 projects certified Silver and Gold under LEED-NCv3 in 10 states in the U.S. (California, Florida, Georgia, Illinois, Massachusetts, New York, Ohio, Texas, Virginia, and Washington) in 2016. The authors reported low certification performance: 51–55 and 61–68.5 points for Silver and Gold, respectively. They concluded that the category achievements for the Silver level confirmed the results previously reported by Wu, et al. [
15]. In particular, the SS, WE, EQ, and IN categories showed intermediate performance (56.0–68.3% of possible points), whereas EA and MR showed low performance (30% and 41% of possible points, respectively).
Pushkar and Verbitsky [
17] studied 1598 projects certified Silver and Gold under LEED-NCv3 in eight states in the U.S. (California, Florida, Illinois, Massachusetts, Ohio, Texas, Virginia, and Washington) in 2012–2017. The comparison analysis of Gold vs. Silver revealed that the EA category achievement showed the highest increase, the SS and EQ category achievements showed intermediate increases, and the WE, MR, and IN category achievements showed low increases, confirming the results presented by Wu, et al. [
13] for projects certified under LEED-NCv2.2.
Notably, all the aforementioned empirical studies of LEED-NCv2.2 and LEED-NCv3 analyzed the issue of certification/category/credit achievement points only, whereas Siew [
18] analyzed the question of the consistency of achievement points in categories with the same level of certification (Certified, Silver, Gold or Platinum). Consequently, Siew [
18], having analyzed 433 LEED-NCv2 projects from the USGBC database in 2013, concluded that the categories SS, WE, MR, IEQ and IN have inconsistent achievement points at each certification level.
The current version, LEED-NCv4 [
5], includes 110 points in total, the same as LEED-NCv3. However, a new category, Integrative Process (IP), with one possible point, was added to the previous categories. The SS category (26 possible points in LEEDv3) was split in LEED-NCv4 into Location and Transportation (LT, 16 possible points) and Sustainable Site (SS, 10 possible points). The WE category was expanded in LEED-NCv4, including new requirements related to the conservation of water used for cooling towers and installation of a water consumption metering system. In LEED-NCv4, the EA category mostly remained similar to LEED-NCv3, with only an increased weight for enhanced commissioning credit (six possible points versus the two in LEED-NCv3). The MR category was reshaped in LEED-NCv4 to introduce new life-cycle-assessment-based requirements regarding building and material optimization, reuse and sourcing, and production of raw materials, building materials, and components. In general, the EQ category in LEED-NCv4 considers issues that were of concern in LEED-NCv3, with only one new credit: acoustic performance. Thus, the empirical evidence of LEED-NCv4 may differ from the empirical evidence for LEED-NCv3 reported previously by Wu et al. [
15] and Pushkar and Verbitsky [
16,
17]. However, to the best of my knowledge, empirical evidence for LEED-NCv4 has not yet been published.
The purpose of this study was to determine the consistency of achievement points in categories and the effect size between possible points and achieved points in categories and credits in LEED-NCv4 Certified, Silver, Gold, and Platinum projects in the U.S. during 2015–2019. This is the first empirical evidence for LEED-NCv4-certified projects. This knowledge may help LEED experts to reduce inconsistencies and correct the currently rarely-achieved credits in next version of LEED-NC toward a proper balance in the performance of LEED categories.
4. Discussion
The findings of this empirical study of new LEED construction projects certified in 2015–2019 reveal no consistency in achievement points in almost all the categories across the projects for the same certification level. In the LT, WE, MR, and EQ categories, wide ranges of achieved points across the projects were noted for all four levels of certification: Certified, Silver, Gold, and Platinum. This inconsistency in first was discussed by Siew [
18], who studied new LEED construction projects from the USGBC database in 2013 and reported large ranges of scores for categories such as SS, WE, MR, EQ, and IN within the same certification level. This means that different projects teams achieved the same certification level through application of the different credits that were easiest for them to attain. This point-based LEED approach has been criticized for years. In 2006, Scott [
29] discussed that the design of truly sustainable architecture is impossible with this LEED point-based approach. In 2010, Chang [
30] argued that LEED does not devote adequate attention to passive building design principles. In 2014, Shaviv and Pushkar [
31] discussed the LEED GOLD Intel Building in Israel, which was designed mainly by improving building energy systems and neglecting passive and low energy building design.
This LEED-NCv4 study also revealed that the SS and EA categories were the best-achieved categories with most credits in these categories being the medium, high, and very high-achieved credits; the WE and EQ categories were the medium-achieved categories with half being medium high-achieved credits; and LT and MR categories were the worst-achieved categories with low-achieved credits. Notably, LEED and other rating systems have been criticized for not considering LCA in their credits [
32]. However, as was revealed in this empirical study, although LEED-NCv4 introduced LCA in four of six MR credits, these were poorly achieved in all four certification levels.
Despite that EQ category being recognized here as a medium-achieved category, only low-emitting materials considered as influencing human health are included, omitting the use of other potentially toxic building materials. For example, LEED requires reducing persistent, bioaccumulative, and toxic chemicals only in healthcare-type buildings [
5].
Moreover, despite EA being the best-achieved category, only LEED-NCv4 Platinum projects achieved a high level for the Optimize energy performance credit. In this credit, reducing operational energy is prescribed considering building-related and system-related features together. Again, passive and low energy building design can be neglected, achieving the required energy decrease through application of HVAC systems with a high-efficiency performance coefficient [
9].
The IN category was found to be only highly achieved in Platinum projects. This empirically confirms that LEED fails to encourage and reward innovation. Cucuzzella [
33] analyzed the best-constructed environmental public spaces and buildings from 1970 to 2010 and argued that contemporary society placed more confidence in rating systems prescribe best-known practices and has less desires to develop innovative and sustainable solutions.
Thus, much more research should be invested in developing a weighted green rating system that will encourage project teams to build environmentally friendly sustainable projects and not only seek easy points to achieve certification.