The fact of conservation is defined as keeping the cultural values from the past alive and providing the sustainability with the concern of transferring them to the next generations and assuring the cultural heritage. Reuse of the monumental buildings, which are identified as spatial traces of common life experience and handled in the scope of conservation, is important for their preservation and evaluation. Reuse of the monumental buildings forms the basis of sustainability understanding and new function happens to be an input to provide the sustainability of the building. According to the sustainable conservation principles, the adaptation of the monumental buildings to contemporary usages is connected to function-building-environment relationships. The utility is a precondition for providing the habitability and sustainability. This can be supplied by evaluating the occupancy process before the conservation applications and directing the interventions. The most important point in Post Occupancy Evaluation is determining the level of utility and habitability. In determining utility and habitability level, conserving the physical and spatial characteristics of the monumental building and keeping them alive are aroused as an important input. It is necessary to provide the new function-monumental building adaptation and fulfill the requirements of its new users and new function in an optimum level for the conservation to be sustainable. It is needed to confirm the spatial and functional necessities of the new function and investigate the fulfillment level of the existing spaces in the monumental building for the new requirements and determine the satisfaction degree of the buildings new users for identifying the new function-monumental building adaptation level.