Abstract
External Thermal Insulation Composite Systems (ETICS) are often used in Europe. Despite its thermal advantages, low cost, and ease of application, this system has serious problems of biological growth causing the cladding defacement. Recent studies pointed that biological growth is due to high values of surface moisture content, which mostly results from the combined effect of exterior surface condensation, wind-driven rain, and drying process. Based on numerical simulation, this paper points the most critical parameters involved in hygrothermal behaviour of ETICS, considering the influence of thermal and hygric properties of the external rendering, the effect of the characteristics of the façade, and the consequences of the exterior and interior climate on exterior surface condensation, wind-driven rain, and drying process. The model used was previously validated by comparison with the results of an “in situ” campaign. The results of the sensitivity analyses show that relative humidity and temperature of the exterior air, atmospheric radiation, and emissivity of the exterior rendering are the parameters that most influence exterior surface condensation. Wind-driven rain depends mostly on horizontal rain, building’s height, wind velocity, and orientation. The drying capacity is influenced by short-wave absorbance, incident solar radiation, and orientation.
Highlights
External Thermal Insulation Composite Systems (ETICS) are often used in Europe since the 70’s, both in new buildings and in retrofitting
Biological growth is due to high values of surface moisture content, which results from the combined effect of four parameters: wetting due to surface condensation, which occurs mainly during the nights with clear sky, wetting due to wind-driven rain, drying process, and properties of the exterior layer (Figure 5)
Where WDR is the wind-driven rain intensity, Rh is the horizontal rainfall amount, R1 is a driving rain coefficient that depends on the construction element, R2 is a driving rain coefficient that depends on the position on the facade, V10 is reference wind speed at 10 m above ground (m/s), and θ is the angle between the wind direction and the normal to the facade (∘)
Summary
External Thermal Insulation Composite Systems (ETICS) are often used in Europe since the 70’s, both in new buildings and in retrofitting. The popularity of this technology grew due to its advantages regarding other techniques of insulation. Three very relevant aspects in the construction industry must be added: low cost, ease of application, and possibility to be installed without disturbing the building’s dwellers, which is important in refurbishment. Past applications of ETICS have revealed some problems, low impact resistance and the cladding defacement due to biological growth. No changes occur in the thermal and mechanical performance of the system, biological defacement has an enormous aesthetic impact, which gathers the building’s dwellers disapproval and restricts the full implementation of this technology
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