Trentepohlia is a genus of filamentous chlorophytes green algae commonly found in association with fungi and bacteria on building envelopes. Their colonies have a characteristic red coloration which results from the production of β-carotene and hematochrome pigments. They are commonly present on walls, roofs and other external building structures and thrive in humid and shaded environments where sufficient moisture is available. Since their growth is strongly influenced by factors such as water availability, time of wetness, substrate temperature, and lighting conditions, the distribution is usually non-uniform and reflects the varying moisture exposure across different parts of a building. Usually, Trentepohlia prevails in areas affected by water rebound, runoff, splashing, capillary rising or accidental water leaks. Moreover, Trentepohlia spotlights intervention restorations done by materials with different thermal conductivity and hygroscopic properties. Given that water is one of the most damaging factors affecting building performance, these algae can serve as valuable bioindicators for detecting the most moisture-affected areas. In this work many case studies regarding tracer properties of Trentepohlia algae will be shown in association with building’s 3D reconstruction, Building Information Modeling, thermal imaging survey and chemical-physical analysis of the growing substrates.