Incorporating façade-specific climatic factors to improve the ISO 15927-3 characterisation of wind-driven rain spells: Dutch and Spanish case studies

ISO standard 15927-3 characterise episodic exposures of wind-driven rain (WDR) on building façades by identifying wetting intervals, referred to as spells. Spells separated by 96 h or more without WDR are considered, assuming that this interval is sufficient for evaporative losses to exceed prior rainwater gains. This approach ignores variations in evaporation due to the façade orientation and local environmental factors, which cause diverse drying intervals even for the same material. This study proposes an estimation of potential evaporation losses in façades, considering their orientation and local climate. Representative drying intervals and enhanced façade-specific WDR spells are identified by combining potential evaporation losses with the directional WDR exposure. The results at locations in The Netherlands and Spain demonstrates that the drying intervals can vary significantly depending on these factors (regardless of the surface materials), which suggests reconsidering the current 96-h ISO model to minimise uncertainties when characterising episodic WDR exposures.