## 1 Introduction
[PERSON] studied four countries, namely Finland versus Sweden (northern Europe) and Turkey versus Spain (southern Europe) [11]. In each of these countries, only LEED-NC v3 Gold projects were evaluated. The author revealed different certification strategies for these countries [11]. For example, in terms of outdoor water saving, Sweden showed better results than Finland, while Spain showed better results than Turkey. However, the author analyzed different types of LEED-NC v3 Gold projects, such as in offices, multi-family residential buildings, industrial manufacturing buildings, public assembly buildings, healthcare buildings, higher education buildings, and data centers, among other buildings, considering every project in one pooled set [11]. Combining such LEED projects with different properties into one group, as in [10] and [11], may lead to incorrect conclusions [8]. For example, healthcare buildings may be more interested in the performance of the EQ category than data centers. An additional example is the installation of different heating, ventilation, and air conditioning (HVAC) systems in small and large offices; small offices usually use decentralized systems (DXs), whereas large offices usually install central HVAC systems [12]. Thus, different HVAC systems may lead to different performance results for the EA category between small and large offices. [PERSON] et al. studied LEED-NC v3 certification strategies in Vietnam [13]. The authors analyzed three certification levels and revealed that several credits showed different values between the LEED Silver and LEED Gold projects, as well as between the LEED Gold and LEED Platinum projects. It was concluded that the revealed LEED certification strategies reflected specific characteristics of Vietnam, including the climatic conditions (i.e., a humid tropical climate). However, building types were not specified in their study [13]. [PERSON] focused on three Mediterranean countries: Turkey, Spain, and Italy [14]. The author studied LEED-CI v3 and LEED-C-and-S v3 Gold projects. These countries are located in areas with similar regional environmental concerns. However, the author found similar performance results between the countries, in terms of the SS, MR, and EQ credits, whereas the WE and EA credits showed different values between these three countries [14]. In this study, building types were not specified. Thus, the certification strategies revealed by [PERSON] et al. [13] and [PERSON] [14] may also suffer from inaccuracies. All of the aforementioned LEED foreign-related studies [5; 9; 10; 11; 13; 14] can be suspected of incorrect data collection processes and, thereby, should be treated with some caution. Moreover, these studies have mostly analyzed newly constructed buildings. However, in Europe, the most urgent issue is the retrofitting of existing buildings, as these represent the main building stock [15]. Retrofitting is a more sustainable process than the construction of new buildings [16]. This is because performing retrofittingby improving insulation and HVAC effectiveness results in less materials being required and less waste generation [17]. However, retrofitting also presents many risks and uncertainties related to the selected retrofitting techniques and approaches, restricted financial and schedule frames, and the significant energy saving payback period [18]. The literature describes several cases of successful implementations of LEED certification in building retrofits. For example, [PERSON] et al. analyzed the option of improving school sustainability in northern Italy through the application of LEED-NC v3 requirements [19]. [PERSON] et al. studied the Chow Yei Ching (CYC) University building in Hong Kong which, in 2015, received LEED-EB v3 Gold certification after the application of energy efficient retrofit measures [20]. [PERSON] et al. used LEED-EB version 4 (v4) certification to suggest green retrofit measures for a museum (Ca' Rezzonico) in Italy [21].