4.1. Production and Living Space Groups: Certification Strategies at the Category Level
Table 2 shows the medians, PASs, and
p-values of six pairwise comparisons between four types of space for LEED-NC v3 categories.
Within the production space group (1a and 1b), SS, WE, EQ, ID, and RP showed the highest achievements (63 ≤ PAS ≤ 100), while EA and MR showed the lowest achievements (32 ≤ PAS ≤ 43). As a result, the difference between 1a and 1b seems to be negative (p ≥ 0.151). Thus, both industrial manufacturing and office space projects used the same certification strategy.
Within the living space group (2a and 2b), SS, WE, EA, ID, and RP showed high achievements (50 ≤ PAS ≤ 100), while MR and EQ showed low achievements (29 ≤ PAS ≤ 45). In almost all comparisons, the difference between 2a and 2b across the LEED categories seemed to be negative (p ≥ 0.081); the exception was the MR category, in which 2a outperformed 2b (seemingly positive: p = 0.0007). Therefore, both multi-family residential and lodging projects used a similar certification strategy.
Thus, both the production space and living space groups showed high achievement in the SS, WE, and ID categories and low achievement in the MR category. These results are similar to those reported by Ma and Cheng [
17]. Those authors analyzed LEED-NC v3 in the USA and concluded that the highest performance was revealed in the SS, EQ, and ID categories, and the lowest performance was revealed in the MR category. According to Wu et al. [
11], SS, WE, EQ, and ID are the most easily accessible categories and do not require large investments, while MR is difficult to achieve given the difficulty of replacing virgin materials with recycled building materials.
However, the difference between 1a vs. 2a, 1a vs. 2b, 1b vs. 2a, and 1b vs. 2b in achieving WE and EQ seems to be positive, as shown in
Table 2. The production space group outperformed the living space group in both the WE and EQ categories (seemingly positive:
p ≤ 0.036). In addition, in cases of 1a vs. 2a and 1a vs. 2b, the industrial manufacturing subgroup had lower achievements than the two subgroups of the living space group (seemingly positive:
p = 0.010 and
p = 0.023, respectively) in the EA category. Lastly, in the case of 1a vs. 2a, the industrial manufacturing space group outperformed the multi-family residential space group in the MR category (seemingly positive:
p = 0.003).
Despite the differences in the certification strategies used by the two space groups, the overall medians were about the same, at 65 and 63 for the industrial manufacturing and office subgroups, respectively (i.e., production space group), and 63 and 65 for the multi-family residential and lodging subgroups, respectively (i.e., living space group) (seemingly negative:
p ≥ 0.058). These medians for the overall gold-certified LEED project achievements are consistent with the results reported by Wu et al. [
11]. The authors [
11] analyzed LEED-NC v3-certified projects around the world and noted that LEED-NC v3-certified projects typically received total points only slightly above the lower thresholds of each certification level. This means that the level of certification matters more than the actual sustainability of LEED-certified projects [
38].
To understand the specific differences between the certification strategies of the production space and living space groups, further analysis of the SS, WE, EA, MR, and EQ credits is presented in
Section 4.2.
4.2. Production and Living Space Groups: Certification Strategies at the Credit Level
4.2.1. Sustainable Sites
Table 3 shows the medians, PASs, and
p-values of six pairwise comparisons between four types of space for SS credits.
Within the production space group (1a and 1b), SSc1, SSc2, SS4.1, SSc4.2, SSc4.3, SSc4.4, SSc5.1, SSc5.2, SSc7.1, and SSc7.2 showed the highest achievements (56 ≤ PAS ≤ 100), while SSc3, SSc7.1, and SSc7.2 showed the lowest achievements (0 ≤ PAS ≤ 22). The difference between 1a and 1b in any of the SS credits seems to be negative (p ≥ 0.07). This means that both industrial manufacturing and office space projects used the same certification strategy for the achievement of SS credits.
Within the living space group (2a and 2b), SSc1, SSc2, SSc4.1, SSc4.3, SSc4.4, SSc5.2, and SSc7.1 showed the highest achievements (63 ≤ PAS ≤ 100), while SSc3, SSc5.1, SSc6.1, SSc7.2, and SSc8 showed the lowest achievements (0 ≤ PAS ≤ 38). In almost all comparisons, the difference between 2a and 2b seems to be negative (p ≥ 0.132); the exceptions were SSc4.2, in which 2a had a lower achievement than 2b (seemingly positive: p = 0.001), and SSc6.2, in which 2a outperformed 2b (seemingly positive: p = 0.001). In this space group, both multi-family residential and lodging projects used a similar certification strategy to achieve SS credits.
A comparison between the certification strategies of the production and living space groups demonstrated statistical differences between these two certification strategies in achieving 5 out of 14 SS credits. In particular, each of the two subgroups (1a and 1b) from the production space group outperformed each of the two subgroups (2a and 2b) from the living space group in both the SSc5.1 and SSc7.2 credits (seemingly positive: p ≤ 0.045). In addition, in cases of 1a vs. 2a and 1b vs. 2a, the two subgroups from the production space group outperformed the multi-family residential subgroup (2a) from the living space group in SSc5.1 (seemingly positive: p = 0.0002 and p = 0.003, respectively). However, the two subgroups (1a and 1b) from the production space group had lower achievements than the multi-family residential subgroup in SSc7.2 (seemingly positive: p = 0.004 and p = 0.003, respectively). Finally, in the cases of 1b vs. 2a and 1b vs. 2b, the office space subgroup outperformed the two subgroups from the living space group in SSc8 (seemingly positive: p = 0.045 and p = 0.013, respectively).
Thus, the two space groups production and living used the same certification strategy, including for the high-achievement urban-infrastructure-related SS credits, such as SSc1 (site selection); SSc2 (development density and community connectivity); SSc4.1, SSc4.3, and SSc4.4 (alternative transportation—public transportation access, low-emitting and fuel-efficient vehicles, and parking capacity, respectively); SSc5.2 (site development—maximize open space); and SSc7.1 (heat island effect—nonroof). This finding was reasonable because the analyzed LEED projects were located in cities (Kalisz, Poznań, Rzeszow, Swinoujscie, Warsaw, Wroclaw, etc.) that have developed infrastructure, including basic services such as schools, supermarkets, banks, etc., and a variety of public transport options, such as buses, metropolitan areas, and railway services.
Ma and Cheng [
17] noted that in LEED-NC v3-certified projects in the USA, SSc1 (site selection) and SSc4.3 (alternative transportation—low-emitting and fuel-efficient vehicles) had high PASs (85% and 81%, respectively). In LEED-NC v3-certified projects in Vietnam, SSc1 and SSc4.3 had high achievements: PAS = 92 and 100, respectively. In addition, SSc5.2 (site development—maximize open space) and SSc7.1 (heat island effect—nonroof) achieved high PASs (69 and 86, respectively) [
39]. This means that these SS credits are relevant in different countries since they relate to issues that are relevant in any modern city with developed infrastructure.
4.2.2. Water Efficiency
Table 4 shows the medians, PASs, and
p-values of six pairwise comparisons between four types of spaces for WE credits.
Within the production space group (1a and 1b), WEc1, WEc2, and WEc3 showed high achievements (86 ≤ PAS ≤ 100). As a result, the difference between 1a and 1b seems to be negative (p ≥ 0.738). Thus, both industrial manufacturing and office space projects used the same certification strategy to achieve WE credits.
Within the living space group (2a and 2b), WEc1, WEc2, and WEc3 showed the highest achievements (50 ≤ PAS ≤ 100). As a result, the difference between 2a and 2b seems to be negative (p ≥ 0.132). Therefore, it can be concluded that the multi-family residential and lodging subgroups used the same strategy to obtain WE credits.
However, in the cases of 1a vs. 2a and 1b vs. 2a, each of the two subgroups (industrial manufacturing and office space) from the production group outperformed the multi-family residential subgroup in WEc1 and WEc3 (seemingly positive: p ≤ 0.008).
Despite this statistical difference in the achievement of WEc1 and WEc3, water conservation was considered a high priority in the certification strategies for both the production space and living space groups. This is because Poland’s water resources are dependent on the Vistula and Odra Basins, and the country is in the low water availability category (1566 m
3/person) [
40].
In other countries with high water consumption, such as Vietnam, all water credits (WEc1–WEc3) were achieved at a high level (88 ≤ PAS ≤ 94) [
39]. Thus, regardless of the type of building, WE credits depend only on the availability of water in a given country. In addition, the installation of irrigation systems (WEc1) and water-saving devices such as toilets, urinals, toilet faucets, showers, and kitchen sink faucets (WEc2 and WEc3) can be easily implemented without requiring large investments.
4.2.3. Energy and Atmosphere
Table 5 shows the medians, PASs, and
p-values of six pairwise comparisons between four types of space for EA credits.
Within the production space group (1a and 1b), EAc4 and EAc5 showed the highest achievements (86 ≤ PAS ≤ 100). In contrast, EAc1, EAc2, EAc3, and EAc6 showed the lowest achievements (0 ≤ PAS ≤ 44). As a result, the difference between 1a and 1b seems to be negative (p ≥ 0.219). Both the industrial manufacturing and office subgroups prioritized/ignored the same EA credits.
Within the living space group (2a and 2b), EAc1, EAc4, and EAc5 showed the highest achievements (61 ≤ PAS ≤ 100). In contrast, EAc2, EAc3, and EAc6 showed the lowest achievements (0 ≤ PAS ≤ 23). The multi-family residential and lodging subgroups chose the same certification strategy to achieve EA credits.
Only in the cases of 1a vs. 2a and 1a vs. 2b did the industrial manufacturing space subgroup show a lower achievement compared with the multi-family residential space and lodging space subgroups in EAc1 (seemingly positive: p = 0.011 and 0.014, respectively).
Thus, both the production space and living space groups prioritized Eac4 (enhanced refrigerant management) and EAc5 (measurement and verification credits), and largely ignored EAc2 (on-site renewable energy), EAc3 (enhanced commissioning), and EAc6 (green power). Poland produces energy mainly from fossil fuels (hard coal, 46%; lignite, 24%; and natural gas, 10%), with the remaining 20% from renewable sources (wind, 10%; biomass/biogas, 5%; water, 2%; and other, 3%) [
41]. This small share of renewable energy explains why both the production space and living space groups showed low achievements in the renewable energy credits (EAc2 and EAc6).
Regarding EAc1, the production space group achieved 5 and 6 points (for the industrial manufacturing and office subgroups, respectively), whereas the living space group achieved 12.5 and 10.5 points (for the multi-family residential and lodging subgroups, respectively). This means that—compared with the building’s baseline performance according to ASHRAE 90.1-2007—the production space group saved 20–22% in operating energy for heating, cooling, and lighting, and the living space group saved 31–35% [
42].
Compared with residential buildings, office buildings consume more operating energy. This is due to the large windows intended for daylight and views and the high internal heat load (large number of workers and computers, high demand for artificial lighting, year-round air conditioning, and use of elevators) inherent to office-type buildings [
25]. This makes it difficult to save operating energy in office buildings compared with residential buildings. The results of this study confirmed that the living space group saved more operational energy than the production space group.
Wu et al. [
11] noted that low achievement in EAc1 could also be a result of development costs for efficient energy projects caused by simulating ASHRAE 90.1-2007 reference buildings and comparison project buildings. The authors [
11] explained that EAc1 energy consumption modeling requires USD 0.15 to 0.30 per gross square foot.
However, this difference in operational energy savings can lead to a significant difference in environmental damage associated with the EAc1 certification strategy in the production space and living space groups. This is because Poland produces 1 kWh of electricity using 80% fossil fuels and 20% renewables, which releases 724 g of CO
2 (three times the European average) [
41]. Taking into account the 210 kWh/m
2·year of operational energy required by buildings located in Poland [
43], the EAc1 certification strategy in the production space group can lead to 5,926,050–6,081,600 g CO
2/m
2·50 years, whereas the strategy applied by the living space group can lead to 4,941,300–5,245,350 g CO
2/m
2·50 years. Thus, in countries with a high proportion of fossil fuels, such as Poland, high achievements in EAc1 have a strong effect on reducing global warming potential.
4.2.4. Materials and Resources
Table 6 shows the medians, PASs, and
p-values of six pairwise comparisons between four types of space for MR credits.
Within the production space group (1a and 1b), MRc2, MRc4, and MRc5 showed the highest achievements (50 ≤ PAS ≤ 100). In contrast, MRc1.1, MRc1.2, MRc3, MRc6, and MRc7 showed the lowest achievements (0 ≤ PAS ≤ 14). As a result, the difference between 1a and 1b seems to be negative (p ≥ 0.219). Thus, the same certification strategy for MR credits was used by both the industrial manufacturing and office subgroups.
The same strategy for MR credits was used by the living space group (2a and 2b): MRc2, MRc4, and MRc5 showed the highest achievements (50 ≤ PAS ≤ 100), and MRc1.1, MRc1.2, MRc3, MRc6, and MRc7 showed the lowest achievements (0 ≤ PAS ≤ 13). The only difference was in the case of 2a vs. 2b, in which the multi-family residential subgroup showed lower achievement compared with the lodging subgroup in MRc5 (seemingly positive: p = 0.005).
The comparison between each subgroup from the production space group with each subgroup from the living space group demonstrated only three differently achieved MR credits. In the cases of 1a vs. 2a and 1b vs. 2a, the industrial manufacturing and office subgroups outperformed the multi-family residential subgroup in MRc5 (seemingly positive: p = 0.0004 and 0.008, respectively). Additionally, in the case of 1a vs. 2a, the industrial manufacturing subgroup outperformed the multi-family residential subgroup in MRc4 (seemingly positive: p = 0.011).
Thus, both the production space and living space groups showed lower achievement in the MRc1.1 and 1.2 (building reuse—maintain existing walls, floors, and roof and maintain interior nonstructural elements), MRc3 (materials reuse), MRc6 (rapidly renewable materials), and MRc7 (certified wood) credits. The LEED gold-certified projects studied here were all new buildings. MRc1 and MRc2 are highly dependent on complex design and demolition efficiency and require additional time and costs to implement [
44]. MRc3 requires salvaged, refurbished, or reused materials [
42]. Reused material is not attractive to potential tenants/owners because of concerns about its quality [
44]. MRc6 requires rapidly renewable materials such as bamboo, wool, or cotton insulation, thereby reducing the use of finite raw materials [
42]. MRc7 is committed to using timber building components such as structural framing, floors, doors, and trims that are certified according to Forest Stewardship Council principles and criteria [
42]. These materials may be considered unsuitable for concrete construction technologies in Poland [
45].
Other studies have also indicated poor performance for these MR credits. For example, MRc1, MRc1.2, MRc6, and MRc7 had low PAS scores (10, 3, 0, and 0, respectively) in LEED-NC v3-certified projects in Vietnam [
39]. MRc1.1, MRc1.2, and MRc6 also had low PASs in LEED-NC v3 projects certified in the USA (20, 0, and 2, respectively) and China (3, 0, and 1, respectively) [
44].
In contrast, both the production space and living space groups showed high achievements in the MRc2 construction waste management and MRc4 recycled content credits. For waste management in Poland, the National Waste Management Plan was elaborated in 2014. This document includes both strategies to prevent the generation of certain types of waste and strategies to reduce the disposal of biodegradable waste [
46]. Thus, since the practice of waste management exists at the national level, it supports high scores in MRc2 and MRc4.
4.2.5. Indoor Environmental Quality
Table 7 shows the medians, PASs, and
p-values of six pairwise comparisons between four types of space for EQ credits.
There was a significant difference between each of the subgroups from the production space group and each of the subgroups from the living space group. Specifically, 1a outperformed 2a in EQc1, EQc2, EQc3.2, EQc4.3, EQc5, EQc7.1, and EQc7.2 (seemingly positive: 0.0001 ≤ p ≤ 0.023); 2a outperformed 1a in EQc6.2 and EQc8.2 (seemingly positive: p = 0.0007 and 0.023, respectively); 1a outperformed 2b in EQc3.1, EQc3.2, EQc4.3, and EQc7.2 (seemingly positive: p = 0.041, 0.029, 0.009, and 0.029, respectively); 1b outperformed 2a in EQc1, EQc2, EQc3.2, EQc4.3, EQc5, EQc7.1, and EQc7.2 (seemingly positive: 0.0003 ≤ p ≤ 0.046); and 2a outperformed 1b in EQc4.1 and EQc6.2 (seemingly positive: p = 0.046 and 0.003, respectively).
However, similar EQ strategies were identified between two subgroups within the production space group and between two subgroups within the living space group. Within the production space group (1a and 1b subgroups), EQc1, EQc2, EQc3.1, EQc3.2, EQc4.1, EQc4.2, EQc4.3, EQc5, EQc7.1, and EQc7.2 showed the highest achievements (50 ≤ PAS ≤ 100). In contrast, EQc4.4, EQc6.1, EQc6.2, and EQc8.1 showed the lowest achievements (0 ≤ PAS ≤ 44). Only EQc4.1 had a better achievement score in 1a than in 1b (PAS = 100 and 43, respectively); 1a outperformed 1b (seemingly positive: p = 0.010). Thus, except for EQc4.1, the industrial manufacturing and office subgroups used the same EQ-credit-related certification strategy.
Within the living space group (2a and 2b subgroups), EQc3.1, EQc4.1, and EQc8.2 showed the highest achievements (50 ≤ PAS ≤ 100). In contrast, EQc1, EQc3.2, EQc4.3, EQc4.4, EQc5, EQc6.1, EQc7.2, and EQc8.1 showed the lowest achievements (0 ≤ PAS ≤ 38). The credits for EQc2, EQc6.2, and EQc7.1 had different degrees of achievement: in the multi-family residential subgroup, PAS = 0, 100, and 0, respectively, while in the lodging subgroup, PAS = 88, 25, and 75, respectively. The lodging subgroup outperformed the multi-family residential subgroup in EQc2 and EQc7.1 (seemingly positive: p = 0.001 and 0.005, respectively), whereas the multi-family residential subgroup outperformed the lodging subgroup in EQc6.2 (seemingly positive: p = 0.005). Thus, within the living space group, only 3 out of 15 EQ credits were achieved differently, and 12 out of 15 EQ credits had the same certification strategy.
Wu et al. [
11] found the highest performance in the EQ credit group, which closely matches the high-achieving credits in the production space group. The authors noted that LEED-NC v3 gold projects received high scores in the following criteria: EQc1, EQc2, EQc3.1, EQ4.1-4.4, EQc5, EQc6.1, EQc6.2, EQc7.1, EQc7.2, EQc8.1, and EQc8.2 (50 ≤ PAS ≤ 100). Wu et al. [
11] assessed office, retail, industrial manufacturing/laboratory, higher education/educational facility, healthcare, warehouse and distribution, service, residential, public order and safety, lodging, and public assembly spaces. In this overall data pool, residential and lodging (“living space”) were represented by only 8% of buildings, while office and industrial/laboratory (“production space”) were represented by 40% of buildings. This is why the high-achieving EQ credits proposed by Wu et al. [
11] are much closer to the high-achieving credits identified in the production space group in this study. Moreover, the EQ certification strategy proposed by Wu et al. [
11] can be considered “average” for all analyzed space-type buildings.
However, the present study revealed two different strategies: the production space group scored highly in 10 out of 15 EQ credits, while the living space group performed highly in only 3 out of 15 EQ credits. The EQ credits concern human well-being and health, such as quality of air, addressed via the installation of carbon dioxide sensors, increased ventilation, and low-emitting materials (EQc1, EQc2, EQc3.1, EQc3.2, EQc4.1-EQc4.4) and thermal (EQc7.1 and EQc7.2) and lighting (EQc8.1) comfort. These issues are very important in industrial manufacturing and office environments, as these spaces employ a large number of workers/employees. Moreover, offices are usually divided into several air-conditioning zones equipped with intelligent ventilation systems with individual controls [
47]. Therefore, it is understandable that the EQ credits were prioritized for the production space group more so than for the living space group.
4.2.6. Summarized Number of Significant Differences
Table 8 shows the summarized number of seemingly positive differences (
p ≤ 0.05) in pairwise LEED credit comparisons between groups (production space versus living space) and between subgroups within each group (industrial manufacturing subgroup versus office subgroup and multi-family residential subgroup versus lodging subgroup). The evaluation is summarized in terms of
p-values and presented in
Table 3,
Table 4,
Table 5,
Table 6 and
Table 7.
There were a limited number of seemingly positive differences (p ≤ 0.05) in pairwise LEED credit comparisons between the industrial manufacturing subgroup and the office subgroup and between the multi-family residential subgroup and the lodging subgroup (1 out of 46 and 6 out of 46, respectively). This confirmed the results at the category level, showing that certification strategies for the industrial manufacturing subgroup and the office subgroup (production space group) were very similar. The same was true for the multi-family residential subgroup and lodging subgroup (living space group), their certification strategies were also very similar.
However, in pairwise comparisons of LEED credits between the production space and living space groups, there were a significant number of seemingly positive differences (p ≤ 0.05) (45 of 184). Thus, the production and living space groups used different certification strategies based on the characteristics of their space types.
4.2.7. Practical Applications
Table 9 provides the recommended certification strategies for production spaces (such as offices, retail stores, manufacturing, and warehouses) and living spaces (such as residential buildings, hotels, and dormitories). These strategies are recommended for buildings located in Poland and other similar regions.