## 2 Research Background and Related Works  
### BIM for Renovation Projects  
As mentioned earlier, renovation and expansion projects in existing buildings are gaining extra traction due to new environmental targets. According to [21; 22], the renovation of nearly 20% of the existing building stock is necessary to become zero-carbon-ready by 2030 to address the climate challenge. However, such projects can be highly complex and would require more delicate coordination of the design and construction, which can be overwhelming for traditional methods in construction. In this regard, ref. [23] provides a detailed comparative analysis between traditional and BIM-based design approaches. Implementing BIM uses and processes in renovation projects is different from new construction projects due to the complexity and uncertainty of information in existing buildings [24]. This also includes the preservation, restoration, and rehabilitation of heritage buildings using BIM [25]. BIM implementation in existing buildings often includes two major activities, i.e., renovation and operations at the same time [6; 7; 26; 27]. In this context, construction methods incorporating BIM have the capacity to effectively tackle numerous key challenges commonly encountered in the planning and execution of renovation and expansion projects [9]. However, the implementation of BIM in renovation projects still faces significant barriers, including low client awareness and consequently limited demand for BIM, the inherent complexity of renovation projects, a shortage of skilled labor for BIM implementation in renovation, and the technical limitations of existing BIM tools [9; 19]. Addressing these limitations requires a better understanding of the role that BIM implementation can play in renovation projects by conducting comprehensive case studies and documenting the practical benefits and challenges. Although many studies have been conducted on BIM implementation and its impact on projects for new construction projects, there have been relatively few studies conducted on the use of BIM in renovation and expansion projects [28]. This gap was specifically emphasized in a recent study by [29], which suggests that researchers should pay more attention to the use of BIM technology in building renovation projects and consider the challenges and stumbling blocks of using BIM technology in building renovation. The limited amount of conducted research in this area may be attributed to the complexity of challenges that projects encounter when implementing BIM in renovation and expansion projects. In this regard, one of the biggest challenges to implement BIM in existing buildings is the lack of models representing the as-is condition, because BIM is often not developed in the original projects [9; 30]. Moreover, in many projects, BIM is only used in the early stages, and as-planned BIM often does not reflect the as-is conditions, because the changes occurring either during the construction or operation phase are not applied to the model. Thus, for complex renovation projects, it is important to create an accurate as-built BIM by capturing the existing building components and generating BIM based on the captured data [31]. Common approaches for capturing the geometric information are tacheometry, photogrammetry, and 3D laser scanning [30]. The 3D point cloud data acquired from laser scanning are applied in the AEC industry for various applications, including 3D model reconstruction, geometry quality inspection, construction progress tracking, building performance analysis, safety management, and more [31]. However, as the author [14] points out that semantic information is not captured automatically by laser scanning, and data processing and model generation are time-intensive tasks [30].