Existing old buildings were considered as the city's culture reminder. By the time, they could be kept via adaptation for contemporary usages. That adopting considered the context of the environmental, social and economic idea of the prior eras, related to the building's life cycle, that guided by local solutions. This paper started with the adaptation process definition with an evaluation of a number of building's state to bring out the different potential outcomes for discussing the future adaptation possibilities, especially that known as “alterations and extensions". Therefore, by rethinking of the new addition's integration into the heritage buildings will support the heritage value and fit new functions to present innovative design process approaches in the field of heritage preservation's design. By analysing some case studies, the study achieved some criteria for designing the alterations and extensions by making them an effective component in the design of old heritage buildings. And finally applying these principles to demonstrate its efficiency.