Use of bio-based insulation materials in buildings: modelling of hygrothermal conditions in use – resistance of a wood fibre material to moulds according to climatic conditions

Abstract

Due to their positive environmental attributes and their performance, the use of bio-based insulation materials such as wood fibre, loose fill cellulose, hemp, flax and straw has been increasing in the construction industry across Europe. However, the current test method requirements to get technical approval do not take into account the real hygrothermal conditions in use. This research project aimed to model hygrothermal conditions of bio-based insulation materials (rigid, semi-rigid and loose-fill). The modelling of coupled thermal and humidity transfers was carried out with WUFI 2D software. Representative wall and roof were studied, with different end uses for insulation materials (outer, inner, distributed insulation). Four unfavourable French climates where studied (cold continental, humid oceanic, Mediterranean, mountain). Regarding modelled hygrothermal conditions and insulation material behaviour, two humidity use classes could be defined. An experimental design was carried out with wood fibre insulation material to assess the impact of temperature and relative humidity on the mould growth. An innovative mould test was developed with a quantitative assessment of mould growth. Finally, corroborating these two parts, this project gave to the manufacturers of biobased insulation materials the option to highlight natural durability of their products, testing them in an environment that fits with the real hygrothermal conditions in use.