The concept of post-tensioned timber structures has been developed and implemented since 2005. The technology relies on un-bonded post-tensioned timber elements to create a moment resisting connection. After several years of extensive experimental testing, the first buildings were constructed from 2010. Although comprehensive research has been conducted on their behaviour under static and dynamic loading, limited data is available about their long-term performance. In particular, there is limited understanding of how to estimate the long-term post-tensioning losses. This paper presents two years of experimental observations on a fully monitored post-tensioned timber building: the House of Natural Resources. Additionally, a numerical approach based on a moisture-dependent visco-elastic model is presented to simulate the post-tensioning trend over time.