## 1 Introduction
Furthermore, IRT can be used for the detection of various hazards, such as seismic activity, or the effect of environmental factors, which are very important issues in terms of the future of cultural heritage protection [14]. Generally, the restoration activity and the monitoring of the intervention should be based on results of combined interpretation of thermal maps with the visual images, and integration with the aid of informatics tools. The first NTUA pioneering applications of IRT started in the early 1990s and until now it has been used at all stages of a conservation project for the investigation of important monuments in Greece, but also beyond the borders of Greece (like Italy and Spain) and Europe (Turkey, Israel). NTUA uses IRT as a crucial part of the process of non-destructive investigation of monuments, along with other non-destructive techniques, such as portable microscope, ultrasonics, georadar, Schmitt-Hammer test, etc. [15]. In all these years, the numeral monuments investigated belong to different historical periods, dating from antiquity (e.g., Apollo Temple in Rhodes, Temple Ifaistos in Athens ancient agora), to Byzantine (e.g., Haghia Sophia in Istanbul, Kaisariani Monastery in Athens), Medieval (Medieval Fortifications of Rhodes), to 1800s reconstructions (e.g., Holy Aedicule in the Holy Selphuchre complex), Neoclassical buildings (e.g., National Archaeological Museum in Athens) and modern cement structures (Spa Kallithea, Rhodes). Additionally, there have been attempts to standardize this technique (e.g., estimation of the emissivity of materials, analysis of all the relevant parameters affecting the application of this technique). As an attempt to set recommendations for the most appropriate use of this technique, previous experiences led to the compilation of protocols for the technique's application [16]. Above all, IRT provides the thermal maps of a surface. These maps can give valuable information about heat and moisture flux and thermophysical properties of materials. All these data, with the aid of the necessary mathematical modelling, and quantitative techniques, along with integratedinformatics tools, can serve as a basis for many different uses and applications, from decay diagnosis, to conservation interventions and monitoring actions. In particular, in the case of cultural heritage, this is a unique benefit, in order to scientifically support maintenance and proper decision making actions on the most compatible conservation materials and interventions and also for the monitoring and sustainability control of large-scale restoration works. A general diagram for the application of IRT in built heritage is shown below (Figure 1). In this work, characteristic examples of IRT application for the protection of cultural built heritage are presented. Also, the use of IRT in large scale conservation projects is discussed. We undertake a case study on the ancient temple of [PERSON] in Rhodes during the diagnostic phase of the project and, before compiling the conservation interventions study, we also study the Holy Aedicule of the Holy Selphuchre in Jerusalem during different phases of the rehabilitation works.