Multi-physics modelling for durability evaluation of ETICS

The External Thermal Insulation Composite Systems with rendering (ETICS) are a building envelope technology widely used both in new construction interventions and in energy refurbishments. Installed ETICS display multiple failure modes, which are often the result of the repeated action of multiple agents inducing cyclic stresses and strains, thus fatigue. In this study, to predict the performance decay over time and to assess the durability, we coupled two numerical models: a hygrothermal model, computing the Heat and Moisture Transport (HMT) in porous media, coupled to a Thermo-Mechanical Finite Element Method model (TM-FEM). The transient temperature profile computed with the HMT model was the input for the TM-FEM simulations, with which we assessed the thermal stress over time, and the frequency of the events exceeding the critical stress thresholds, beyond which the base coat is subject to fatigue. As variables, we considered the moisture response of the base coat, and the optical properties of the finishing coat, in a set of Southern European climates. Especially we focused our attention on the frequency of thermal shocks and freezing-thawing cycles in HMT analysis as the main causes of cracks in case of temperature variation in a preliminary 3D TM-FEM model analysis.