There is a growing interest in low-tech technologies, drawing on the tradition of building with organic and unprocessed materials. One such technology is straw bale constructions. This paper presents an example of a timber-frame building in which straw bales were used as wall filling. The building is located in northern Poland and is a small, year-round single-family dwelling. Based on the available literature and experimental studies, it can be concluded that straw bale technology carries several potential threats related to the selected technology, quality of workmanship, and climatic conditions. The article describes the measurements of the air tightness of the building, the heat transfer coefficient U and the analysis of the humidity of straw walls. The study results confirm the risks related to the low air tightness of the building and the risk of water vapour condensation in the external partitions.