Retrofitting traditional walls: A comparative study on thermal renders and more common insulation materials.

To reach the European climate-neutrality by 2050, the strategic importance of a large energy-efficient renovation of the existing building stock is clear. Among the several retrofit solutions that can be adopted to reduce the impact of existing buildings, the addition of thermal insulation to external walls is often considered. From the building physics point of view, external thermal insulation is considered to be safer than interior one since it entails reduced risks of condensation. Nonetheless, unforeseen moisture accumulation may occur after the intervention, when dealing with traditional porous walls. To avoid moisture-related problems, correct insulation solutions must be chosen, accounting for moisture dynamics in the envelope. This study takes into analysis the massive walls of a traditionally constructed building located in the temperate climate of Lisbon. The hygrothermal behaviour of the walls, in their original and retrofitted configurations, is evaluated by means of mono-dimensional dynamic simulations. The thermal insulation solutions considered are three thermal rendering systems that are commercially available in Portugal, and they were characterized through experimental tests. For the sake of comparison, two more common insulation materials were also considered. Results show the importance of the parameters A_w (capillary water absorption coefficient) and s_d (air-equivalent thickness) of the materials adopted in the retrofit. Furthermore, this study shows that for traditional porous walls the retrofitted configurations should be simulated not only under operational conditions, but also considering the drying from a very high-water content. If the latter scenario is not accounted for, moisture accumulation may be overlooked. [ABSTRACT FROM AUTHOR]