As wind-driven rain is one of the most important moisture sources for a building envelope, a reliable prediction of the wind-driven rain load is a prerequisite to assess the durability of a building facade. To incorporate wind-driven rain in HAM models (heat, air and moisture), many factors should be taken into account. Not only building geometry, wind speed and wind direction, raindrop size distribution, etc. influence the rain load on buildings, but also phenomena such as raindrop impact, absorption, evaporation and runoff should be taken into account. The following is an excerpt from ‘influence of facade materials on runoff due to wind-driven rain’ by T. Van den Brande et al (2012). A full text is available upon request.