Thermal and hygric properties of biomaterials suitable for interior thermal insulation systems in historical and traditional buildings

Historical and traditional buildings account for 10–40% of the building stock in various countries and regions. Retrofitting of their building envelopes aimed at the improvement of thermal performance is often feasible using interior thermal insulation systems only. The effectiveness of systems without vapor barrier depends on the application of modern insulation materials with enhanced water transport properties contributing to fast liquid moisture redistribution and mitigating the risks related to water vapor condensation. In this paper, thermal and hygric properties of several biomaterials potentially applicable as thermal insulation boards on the interior side of historical building envelopes are investigated. The obtained experimental data include all transport and storage parameters necessary for appropriate hygrothermal- and energy-related assessment of buildings provided with interior thermal insulation systems using advanced computer simulation tools. Wood fiberboard, flax fibers, hemp fibers, jute fibers, and sheep wool are found to have, at the same time, low thermal conductivity (∼0.05 W m−1 K−1) and high moisture diffusivity (1.1 × 10−6 – 1.2 × 10−5 m2 s−1) which can classify them as good candidates for the use in interior thermal insulation systems without water vapor barrier. They exhibit convenient water vapor diffusion parameters and hygroscopic properties as well, which favors their use on the interior side. The natural origin presents another benefit. In a comparison with conventional materials (calcium silicate, hydrophilic mineral wool) having similar thermal and hygric properties, they bring more harmony to the process of retrofitting historical building envelopes.