Biological Colonization on External Thermal Insulation Composite Systems (ETICS): Water Performance, Aesthetic Appearance and Onsite Monitoring

Abstract

The European Union has been progressively introducing sustainable environmental policies which aim to improve the energy performance of new and existing buildings towards a climate-neutral building stock by 2050. As a result, the use of External Thermal Insulation Composite Systems (ETICS) has been increasing in both new and thermal retrofitted façades to enhance the level of thermal insulation of the building envelope (i.e., lowering reference U-values). However, the enhanced thermal performance of these systems can have impact on their long-term durability, thus potentiating further anomalies. For example, greater values of thermal resistance may lead to a decrease of surface temperature during the night, thus increasing the risk of surface condensation and favoring biological colonization. This paper aims to investigate the influence of the hygrothermal behavior of three ETICS with different rendering systems and thermal insulation composition to withstand biological colonization. All systems were exposed outdoors at an urban site in Lisbon, Portugal, facing North. The surface temperature, the surface relative humidity and the meteorological conditions were monitored for four months. At the same time, the capillary water absorption and the aesthetic properties of the systems were evaluated after 6, 9 and 12 months of outdoor exposure. Moreover, biological colonization was visually assessed using a previously defined rating scale. The onsite monitoring results were then compared with the water performance, aesthetic properties and biological colonization observed throughout natural aging. The highest level of biological development was obtained for the lime-based ETICS with ICB thermal insulation, which also presented the highest capillary water absorption and color alteration after one year of natural aging. On the other hand, the silicate-based system obtained the highest risk of surface condensation, and no biological growth was detected in this system during the exposure period.