The use of bio-based materials offers an eco-friendly solution to reducing building energy consumption. However, their adoption remains limited due to a lack of understanding of their hygrothermal performance compared to conventional materials. This study seeks to address these challenges by thoroughly analyzing the hygrothermal characteristics of bio-based materials across three scales: composite material, wall, and building scales. At the composite material scale, the hygrothermal properties of various bio-based concretes and insulation boards are systematically reviewed. At the wall scale, the hygrothermal behavior of wood-cement concrete walls is examined under diverse climatic conditions. Finally, at the building scale, the energy performance of structures utilizing hemp concrete is compared with conventional buildings, focusing on heating and cooling energy consumption. This multi-scale investigation aims to advance the practical implementation of bio-based materials in sustainable construction and contribute to the broader adoption of eco-friendly building practices.