Experimental assessment of the water content influence on thermo-acoustic performance of building insulation materials

Nowadays, a large number of materials for thermal and acoustic insulation are available on the market. Therefore, some criteria need to be defined to support designers in the selection, which should be based, among other properties, on the overall assessment of the thermo-acoustic and hygrometric performance, at the aim of ensuring good energy performance of the buildings and adequate acoustic comfort conditions. The influence of water content on thermo-acoustic performance of insulating materials is a topic that deserves special attention. However, the analysis of the scientific literature shows that this aspect has always been underestimated, especially in the acoustic field. Insulating materials react differently to the absorption of water, which depends mainly on its origin and structure. If placed in a high humidity environment, an insulating material may adsorb part of the water vapour contained in the air. Then, water vapour can be accumulated inside its porous structure, even in significant quantities, in relation to the weight of the material, so affecting its thermal and acoustic properties. Five different insulating materials used in the building sector were selected for the present study: mineral wool, polyurethane foam, melamine foam, kenaf and cork. Samples were conditioned in a climatic chamber at defined conditions of temperature and relative humidity, and tests of thermal conductivity with a hot disk apparatus and of sound absorption coefficient with an impedance tube were performed. A total number of 190 tests of thermal conductivity and 370 tests of sound absorption coefficient allowed to collect data in order to assess how these properties are affected by water content and if the effect varies for different materials. Results of thermal conductivity tests show a raise with increasing water contents; this outcome was expected, since water is worse than air as a thermal insulator, however, the way water content and thermal conductivity are correlated is different for the studied materials. As far as the influence of water content on sound absorption, which data are hard to find in scientific literature, results demonstrate that moisture does not affect significantly acoustic performance; nevertheless, for some of the examined materials, i.e. those of natural origin, a correlation between the two parameters exists.