Hygrothermal Behaviour of the Timber-Framed Sauna with Straw-Bale Walls

In the autumn of 2016 a timber-framed sauna with straw-bale walls was built for testing hygrothermal properties of walls during permanent usage. The main dimensions of the building's plan were 6.58 x 4.08 m with two rooms on the ground floor: a resting room and a room for washing and wetting (sauna part). The thickness of walls depended on the straw-bale dimensions which were 50 cm. External surfaces of the walls were plastered with the lime plaster. Both clay and lime plasters were used inside to check a better plaster variant for straw. Measuring devices and sensors to determine the temperature and relative moisture content were mounted into walls during construction. The heat flux rate through the wall was measured with a heat flux plate; data were recorded by an Almemo data recorder. Measurements began in December 2016 and ended in April 2017. The heating procedure of the sauna took place once a week. Meanwhile the sauna was heated with electric batteries. The measuring results were interesting. During the heating time the temperature inside the steam room rose to 83 degrees C, but in the middle of the wall it was 23 degrees C. At the same time the external temperature was about 0 degrees C. The data based calculation of thermal transmittance of the wall was U = 0.15 W/m(2)K which was a little lower than predicted.