This work presents an application of the Principal Component Analysis (PCA) technique to detect damage in a beam-like structure. Quite often modal parameters of real structures are more influenced by environmental conditions, such as temperature and humidity, than by damage effects. The PCA method is shown to be able to eliminate the dependence on the external factors and hence the novelty analysis can be used to quantify the damage level. This paper deals with a theoretical study of a beam-like structure, whose Young's modulus varies with the temperature. A numerical and an experimental examples (based on a clamped-free beam mounted in a controlled temperature chamber) are presented to show the reliability of the theoretical analysis and to study the combined effects of the temperature and damage on a structure. An investigation on the boundary conditions effect (i.e. the non-perfectly clamped edge) is performed to understand the relation between the changes of the clamping conditions at one end of the beam and the results of the damage detection. Results are fully satisfying and can be used to investigate on clamping conditions, as well as the presence of damage along the beam when testing beams for laboratory purposes, such as the classical Oberst technique for damping evaluation.