This paper compares experimental results obtained on ancient buildings, following the usual qualitative inspection with a procedure based on time-domain analysis. The aim of the project was to study relationships between characteristics of defects and thermal behavior of the surface, using thermal scanning in various conditions. The other topic was to prove generally the usage of solar radiation as a heating source in thermal scanning. The 'Palazzo della Ragione' in Milan is more than 700 years old. We gave our attention to the upper part of the building. The conditions and damages of facades have been studied also using knocking tests. Defects we are looking for are delamination of plaster on the brick wall. The southward facade has been monitored 6 times during 1993 - 1995, using thermography. In addition, the actual weather conditions during scanning were measured. The results were qualitatively analyzed. A lot of knowledge is needed for the qualitative interpretation of thermograms, because different kinds of defects and structure variation may be confused. Because of limiting factors, any clear correlation between the temperature changes and the detected damages of coating cannot be found based on the first approach. A new series of tests has been made in October 1995. Experiments have been carried out also at a laboratory on a segment of wall, including known defects at various depth. A numerical simulation of the temperature pattern and its time evolution, during the heating and cooling of the wall, was also performed. The dynamic test has been planned, based on the experience of these preliminary studies. Experimental and simulated data have been compared for laboratory and in situ dynamic tests.