  The characterization and monitoring of buildings is an issue that has
attracted the interest of many sectors over the last two decades. With the
increasing use of permanent, continuous and real-time networks, ambient
vibrations can provide a simple tool for the identification of dynamic building
parameters. This study is focused on the long-term variation of frequency and
damping in several buildings, using the Random Decrement Technique (RDT). RDT
provides a fast, robust and accurate long-term analysis and improves the
reliability of frequency and damping measurements for structural health
monitoring. This reveals particularly useful information in finding out
precisely how far changes in modal parameters can be related to changes in
physical properties. This paper highlights the reversible changes of the
structure's dynamic parameters, correlated with external forces, such as
temperature and exposure to the sun. Contrasting behaviors are observed,
including correlation and anti-correlation with temperature variations.
