Strengthening of the RC columns is required due to the design errors; damage due to earthquake or changes in the functionality of the structure, etc. This project involves the repair and retrofitting of G+3 storey school building and its further extension up to G+ 5 storey. Due to this extension, the structure may not be able to carry the additional loads acting upon it. Hence for this purpose the existing structural elements should be strengthened. Various retrofitting methods can be used for the strengthening of the building. The most suitable methods for the strengthening of structure are RC Jacketing of the structural members, Fiber Reinforced Plastic bonding method, steel plate bonding method, strengthening by External Prestressing, etc. Retrofitting is used to enhance the load carrying capacity, increases stiffness, strength and ductility of the existing structure. Therefore, the building would result into safe and stable structure.