Impact of climatic parameters on rain protection layer design for refurbished historic buildings

The application of interior insulation systems consistently increases energy performance of historic buildings, but also severely affects the drying potential of their envelopes reducing the evaporation potential towards the internal side. This reduction is even more critical in façades interested by a significant amount of driving rain. To face this problem, current recommendations and standards suggest the replacement of the original plaster with a “water repellent” one especially in climates with a high yearly horizontal precipitation. However, since this kind intervention represents a big economic and environmental cost, more specific studies are needed to identify whether it is always necessary. In fact, current approach excludes the impact of solar radiation, which may play a significant role for evaporation phenomena. Moreover, wind effect may be taken into account by considering the wind driven rain instead of horizontal rain amount. In order to investigate these hypotheses, this simulation-based study analyzes hygrothermal performances of an internally insulated wall in several European climates and latitudes, with similar annual precipitation and different solar radiation amount and wind conditions. Results show that considering wind action is important to give a more precise estimation of the effective rain impacting the façade. Moreover, water repellent exterior plasters could be avoided in façades with consistent amounts of solar radiation. Consequently, there is currently the need of a more elaborated method for identifying the necessity of replacing the historic external plasters; this method should include external climate factors, as e.g. solar radiation and wind action.