Field Study of Wind Driven Rain Penetration into Vinyl Sidings and Stucco-Clad Wood-Frame Wall Systems at Window Sill

According to the 1996 survey of building envelope failures in the West coast climate of British Columbia (BC), 23% of the failures were related to windows and their interface around the rough openings on the walls. Moreover, rain was found to be a significant moisture source to water penetration through wall assemblies. A study is presented here on the correlation between wind driven rain (WDR) as the moisture source and the relative proportions of water penetration at intended defects (openings) at the interface of windows and walls. In this field investigation, eight full-scale exterior wall panels with vinyl sidings and concealed barrier stucco claddings were built and installed on a field testing station, subjected to real BC climate. From November 1, 2013 – June 19, 2014, rainwater was collected and measured instantaneously from vulnerable detail locations, such as at window sill and at missing sealant defect locations, and then synchronized to the weather data to estimate the potential rain load that may contribute to a leakage into the wood framing assembly. Leakage amounts of approximately 0.5% and 1.5% of WDR were estimated from the sill corner locations of vinyl sidings and stucco-clad test walls, respectively. Although high solar exposures on these South East facing walls facilitated the drying process, the sheathing membranes on the stucco-clad walls were found to experience high amounts of moisture loads. These results are useful for fine-tuning the principal moisture load that is applied in hygrothermal performance assessment and design of exterior wall systems