## 4 Discussion
In this context, the lack of mandatory anchoring of LCA in the tendering and awarding process, as well as award decisions based on financial aspects, i.e., the principle of the lowest bidder, were highlighted. In the political context, both the lack of regulatory control, which could be either performance-based or prescriptive, and the lack of a comprehensive environmental strategy for public projects were described as obstacles. Moreover, the leadership of government and professional institutions must be introduced to green procurement if greener procurement is desired. At the economic level, an approach to financing the additional effort involved in conducting an LCA needs to be developed. Instruments such as environmental management control in the pre-procurement and post-procurement phases or climate funds could help here. Furthermore, within the economic category, additional costs due to increased time and effort were mentioned. In summary, most of the obstacles were found in the methodological and organizational categories. The reasons for not applying LCA were the lack of comparability between different LCA tools, the high complexity of the LCA process, and the lack of information, e.g., user-friendly guidelines, handbooks, or toolkits. These problems were amplified by the missing environmental knowledge within existing organizations and the lack of limited knowledge connected with LCAs. In addition, in most organizations, there are fewer green alternatives and often no access to the necessary data to perform an LCA. It can be argued that most of the obstacles in the three categories of methodological aspects, organizational aspects, and economic aspects can be removed more quickly if appropriate measures are taken at the political and legal levels. However, it must be mentioned that the classified obstacles occur occurred at different levels and are, therefore, not directly comparable. Furthermore, these levels of obstacles were also interrelated and therefore influenced each other. In particular, methodological obstacles influence political and legal obstacles and vice versa. If there are too many methodological obstacles, it is difficult for policymakers and legislators to take the next steps toward mandatory LCA implementation in the building procurement processes. Not to be neglected in this context is the assessment of the cost efficiency of buildings. In the EU Directives, the concept of life cycle costing (LCC) was mentioned in Article 68. It stated that an _\"LCC may also include the costs of externalities (such as greenhouse gas emissions).\"_ This requires the use of LCA in the procurement process to calculate GHG emissions. Life cycle costing remains optional, but according to Article 68(3), life cycle costing became mandatory when there was a common EU methodology [107]. The limitations of the study lay in the selection and number of databases. Over the course of the SLR, the databases ScienceDirect and Scopus were used. Further limitations concern the constraints that were made within the SLR. The search period was limited to the years 2000 to 2020. Regarding the defined keywords, the performed SLR only included articles that fell under the defined keywords and the search strings produced by combination with the Boolean operators. Other synonyms for the defined keywords were not taken into account. However, it should be mentioned that the selected keywords are the frequently used technical terms in the procurement process of buildings and the application of LCA. Only review and research articles in the English were used for metadata analysis. No gray literature was thus considered. Country-specific documents and documents in languages other than English were therefore not included. Finally, there was another limitation regarding the exclusion and assessment of publications. No assessment of publication bias was made. However, the study selection was performed by two reviewers, thus using the double-check principle to avoid subjective assessment.