A Discussion on Winter Indoor Hygrothermal Conditions and Hygroscopic Behaviour of Plasters in Southern Europe

In Southern European countries, due to the specific climate, economy and culture, a permanent heating practice during winter is not widely adopted. This may have a significant effect on the performance of indoor coating materials, typically tested considering hygrothermal conditions in the range of 33–75% relative humidity (RH) and 20–25^◦C, which are common in continuously heated buildings. In this study, the indoor climate of four bedrooms located in Lisbon, Portugal, was monitored under operational conditions. Based on the data monitored in the case studies, characteristic ranges of indoor hygrothermal conditions were defined and compared to those considered in standard test procedures. In addition, numerical simulations were adopted to compare the hygroscopic performance of four plasters under operational conditions observed on-site. Results show that the four rooms, intermittently heated or unheated, do not provide comfort conditions over 50% of the wintertime, with temperatures lower and RH higher than the ones recommended by the standards. The MBVs resulting from simulations (under operational conditions) are qualitatively in agreement with the MBVs obtained under standard testing conditions. Nonetheless, future studies are recommended to evaluate if standard tests are quantitatively representative of the hygroscopic performance of coating materials in the Southern European scenario.