The segmentation of point clouds obtained from existing buildings provides the ability to perform a detailed structural analysis and overall life-cycle assessment of buildings. The major challenge in dealing with existing buildings is the presence of diverse and large amounts of occluding objects, which limits the segmentation process. In this study, we use unsupervised methods that integrate knowledge about the structural forms of buildings and their spatial dependencies to segment points into common structural classes. We first develop a novelty approach of joining remotely disconnected patches that happened due to missing data from occluding objects using pairs of detected planar patches. Afterward, segmentation approaches are introduced to classify the pairs of refined planes into floor slabs, floor beams, walls, and columns. Finally, we test our approach using a large dataset with high levels of occlusions. We also compare our approach to recent segmentation methods. Compared to many other segmentation methods the study shows good results in segmenting structural elements by their constituent surfaces. Potential areas of improvement, particularly in segmenting walls and beam classes, are highlighted for further studies.