In the adaptation process of heritage buildings new extensions are required to create additional spaces because of the functional changes. Masonry structures bring some limitations while adding new extensions, however these challenges make building unique in terms of identity. This research investigates the relationship between the existing building and its extension in terms of structural system and design approach. The data is collected through analysis of the buildings, which take place in the literature. 20 case studies are selected randomly from the literature and categorized according to the location of the extension within the existing building. Secondly, effect of extension to the structure and the design approach has been examined. Lastly, an empirical research has been done under the light of the analysis. The study emphasizes the constraints that must be cared in the extension design. It claims to be a reference for the designers that are working on contemporary extensions and heritage buildings. The main goal of the research is to raise the awareness of the issue and to create a base for the other researchers as a guideline to develop this study further.