The material and mechanical properties of wood are influenced by the changes in environmental conditions where moisture content and temperature are particularly important. This study presents a detailed analysis of the evolution of the dynamic properties of a six-story lightweight timber frame building in Sweden over a nine-month monitoring period. A permanent monitoring system, consisting of a data acquisition system and three accelerometers, was installed at the roof level in May 2024. The system is recording the building’s accelerations four times per day for a duration of fifteen minutes each session, resulting in approximately one thousand datasets over the monitoring period. Additionally, a monitoring system for environmental data was installed, measuring temperature and humidity at 18 different measurement point within walls and slabs since construction.

A comparative analysis of the results obtained under varying temperature and humidity conditions was able to show the impact of environmental conditions on the building's dynamic properties. Recorded data show that, on the one hand, a decrease in temperature can lead to an increase in natural frequencies, indicating a structural stiffening, while a decrease in humidity and moisture content generally results in a decrease in the natural frequency’s values.

The importance of incorporating environmental factors into broader structural health monitoring schemes of timber structures is crucial, particularly since changes of environmental conditions could mask the influence of structural damage in the building.