Biological Defacement of External Thermal Insulation Composite Systems

Abstract

External Thermal Insulation Composite Systems (ETICS) are nowadays often used in Europe. Despite its thermal advantages, low cost and ease of application, this system has serious problems of microbiological growth causing the cladding defacement. This chapter presents the results of a detailed experimental study that was carried out in order to assess the hygrothermal behaviour of facades covered with ETICS, namely to evaluate the influence of orientation on surface humidification, by external condensation and by wind-driven rain. A building located in the University of Porto campus, with its four facades facing the cardinal directions, was monitored during one year. The exterior surface parameters under study were temperature and wind-driven rain. The building interior conditions and the exterior climate were also measured. The tests results were compared with the results of the numerical simulation performed using a commercial hygrothermal model. The conclusions about the results of the experimental and numerical study, their comparison and all the difficulties found to achieve similar results are pointed. This chapter also presents a methodology to assess the risk of biological growth, based on the definition of indices, which combine the effect of surface condensation, wind-driven rain and drying process, three of the most prevalent parameters influencing the surface moisture content. The proposed indices were calculated using data collected during the “in situ” test campaign, which provided information about the exterior climate conditions, the surface temperature and wind-driven rain on four facades covered with ETICS facing the cardinal directions. The indices were compared with the results of the surface relative humidity measured simultaneously that allowed the validation of the methodology. An example of the practical use of this methodology is also presented in this chapter, with the definition of hazard classes of biological defacement of facades covered with ETICS located in the Portuguese territory.