## 4 Discussion  
The increase in the number of new buildings due to rising urbanization increases the share of CO2 emissions caused by the construction industry. Current tendering and awarding practices for buildings are mainly focused on minimizing cost and almost completely disregard environmental criteria when awarding contracts. However, standards and tools, like LCA, for assessing the environmental performance of buildings are already available. There are only a few real case examples of implementing LCA in building procurement processes [50]. The determination of obstacles to applying LCA at this early project stage is still ambiguous. Identifying these obstacles will help project stakeholders avoid these hurdles in advance and thereby reduce CO2 emissions emitted by the construction industries through more environmentally friendly tendering and awarding procedures. For the state-of-the-art identification of LCA implementation in the procurement process of buildings, and thus for the determination of obstacles, an SLR was conducted. The SLR results show that the implementation of LCA in the procurement process of the construction industry is scarcey addressed in the scientific literature. This is the case despite the fact that the concept of procurement is constantly developing in the direction of environmental procurement in European directives and national action plans with terms such as green procurement, sustainable procurement, and environmental procurement. The identified obstacles to overcome were summarized within the following five categories (i) methodological obstacles, (ii) organizational obstacles, (iii) legal obstacles, (iv) political obstacles, and (v) economic obstacles. The classified obstacles were divided into general and specific obstacles. While methodological obstacles occurred due to the LCA method itself and are not directly related to the tendering and awarding process of buildings, specific obstacles, i.e., organizational, legal, political, and economic obstacles, occurred directly due to LCA implementation in the building procurement process. At the methodological level, an approach to implementing LCA in procurement was to establish a well-accepted methodological framework and transparency regarding the use of methods and data. Additionally, the need to develop LCA tools for the whole building was expressed in the literature. For better decisions, and as well in combination with different methods, LCAs should be used as a decision-making tool to judge various alternatives and their environmental implications. For example, the method of comparative LCAs or EPDs was used to push alternatives with lower environmental impacts [28]. The application of environmental criteria could be integrated into the tendering of building services and construction contracts. Another approach was to implement criteria in the preliminary architectural competition [100]. At the organizational level, managers and leaders are crucial when it comes to incorporating environmental preferences into policy documents. Another starting point for improving the situation for LCA in tender documents is the importance of communication and coordination between stakeholders. Improving skills and knowledge transfer, as well as strengthening capacity regarding LCA and awareness of the topic in general, played an important role. Especially education and training regarding the topic of LCA and environmental issues of relevant stakeholders were important. Another important prerequisite for conducting LCA is high-quality LCA data that is scientifically sound, consistent, reliable, and comparable. At the legal level, appropriate guidelines, tools, and manuals are needed to provide the necessary knowledge for LCA and its mandatory implementation. In addition, standardized methods for the assessment of construction products would be beneficial and should be regulated at the legal level.