Laboratory and In-Situ Measurements for Thermal and Acoustic Performance of Straw Bales

This paper investigates the performance of timber-framed walls insulated with straw bales,and compares them with similar walls containing expanded polystyrene (EPS) instead of straw bales.First, thermal conductivity, initial water content, and density of the straw bales were experimentallymeasured in a laboratory set-up, and the dependence of the thermal conductivity of the dry materialon temperature was described. Then, the two insulation solutions were compared by looking attheir steady and periodic thermal transmittance, decrement factor, phase shift, internal areal heatcapacity and surface mass. Finally, the acoustic performance of both wall typologies was analyzed bymeans of in situ measurements in two-story buildings built in Southern Italy. The weighted apparentsound reduction index for the partition wall between two houses and the weighted standardizedlevel difference for the façades were assessed based on ISO Standard 16283. The results indicate thatthe dry straw bales have an average thermal conductivity of k = 0.0573 W/(m ·K), and their densityis around 80 kg/m3. In addition, straw bale walls have good steady thermal performance, but theystill lack sufficient thermal inertia, as witnessed by the low phase shift and the high periodic thermaltransmittance. Finally, according to the on-site measurements, the results underline that the acousticperformance of the straw bale walls is far better than the walls adopting traditional EPS insulation.Overall, the straw bales investigated are a promising natural and sustainable solution for thermaland sound insulation of buildings.