Avoiding the need to directionally determine the exposure to rainwater penetration for façade designs

The damaging effects caused by the penetration of rainwater into building facades require considering for their design the exposure to the two main climatic factors inducing this penetration: wind-driven rain and the simultaneous wind pressure. The characterisation of these exposures for each possible facade orientation of a building requires analysing exhaustive wind direction records, which significantly increases the calculation effort and prevents calculation in locations without such records. This study examines the possibility to avoid this directional analysis, equally obtaining a functional and reliable exposure characterisation. For this purpose, daily climatic datasets were analysed from 920 weather stations subjected to various environmental and topographic conditions in Mexico, Norway and Spain, and the directional and scalar exposures to wind-driven rain and driving-rain wind pressure were determined at each location. The results show that the maximum directional exposure can be adequately approximated using the scalar exposure value, without the use of wind direction records. Considering the usual constructive practice of using a single facade design for the entire building, this simple and functional characterisation of the expected exposure on the most unfavourable orientation provides a significant support for the design decisions of practitioners.