In recent years, a new urban transformation process has been started to minimize the seismic hazard risk in Turkey. The main aim of this process is to avoid uncontrolled urbanization and faulty structuring by replacing old buildings with new seismic-resistant structures. Unfortunately, it brings new risks. The most important risk is formed with the damages which may occur on the adjacent buildings during the demolition. There are several cases and lawsuits reached to local authorities and courts about this issue. The main cause of these damages is the violation of the rules in regulations and ignorance of engineering principles related to demolition applications. In this study, a low-strength building in Istanbul is investigated which has been damaged by the demolition of an adjacent building. The effects of these damages to the seismic performance level of the building are analyzed with three different numerical models. Primarily, both seismic performance levels of undamaged and damaged states are evaluated using nonlinear analysis method. Furthermore, a new structural member is added to the analysis model using the damaged state’s results to strengthen the damaged zone. The local structural behavior of the damaged zone and overall seismic performance of the building are investigated by three different cases aforementioned above to assess the results of this kind of damages. As a result of this study, the necessary strengthening approach is revealed by means of strengthening the local damaged zone or whole structure to provide necessary seismic performance level of the low-strength buildings having this type of damages.