The conservation of historical buildings via charters, general principles, methods for maintenance and repair of the buildings have been analysed in the international environment. Theories, approaches and conservation methods have been adopted along with the developing technology in relevance with the current conditions. Conservation is a process including consistent, coordinated and programmed activity of study, prevention (limiting situation of risk), maintenance (controlling the conditions of property) and restoration (direct intervention). In this regard, the significance of non-destructive tests on existing historical buildings -in the context of planned conservation- should be highlighted, and become widespread. In a country like Turkey which includes extensively rich comprehesive historical building stocks, it is a difficult task to appraise the physical conditions of all historical buildings by non-destructive tests with a limited number of experts. On the contrary, appraisal of present conditions of building stocks and detailed diagnostics phase of the buildings are important in terms of conscious and sustainable conservation. The buildings under the effect of interior and ambient environmental conditions and decays that are developed on building envelope or structural elements due to these conditions affect the structure and thermal comfort conditions in a negative way. Continuous monitoring of these actions causing decay and degradations prevent the structure to be under high risk and necessitates heavy interventions on buildings. By the non-destructive test applications during monitoring, the buildings are prevented to be under high risks and the necessity for heavy interventions can be eradicated.