Wind-Driven Rain (WDR) is one of the major moisture sources that cause building envelope failures. The quantity and spatial distribution of WDR are important considerations for durable building envelope designs and are essential boundary conditions for hygrothermal modelling. Within a comprehensive research program of quantifying WDR exposure of buildings and the effectiveness of overhang on reducing WDR wetting, a six-storey building located in Vancouver, Canada was instrumented for field WDR measurements. One of the challenges in field WDR measurements is the validity of on-site wind measurements. The accurate measurements of on-site wind conditions are essential for correlating WDR on façade with on-site weather conditions and for generating the spatial distribution correction factor required in the semi-empirical WDR models. This paper focuses on discussing the procedure necessary for proper on-site wind measurements for quantifying WDR on façade based on field and wind-tunnel measurements. The proper procedure to calculate the spatial distribution correction factor, namely wall factor according to ISO standard, and its impact on the accuracy of the ISO model is also discussed. The accuracy of ISO model can be significantly improved by using more detailed wall factors calculated based on high-resolution on-site wind and rain measurements.
Wind-driven rain (WDR) is one of the main sources of moisture damages in buildings. Roof overhangs are a common feature that can be used to reduce WDR on building facades. However, there is very limited information on the quantitative evaluation of the effectiveness of overhangs in reducing WDR on building façades, especially through field measurements. A six-story building with a low-sloped roof located in Vancouver has been equipped with a retractable overhang along with a rooftop weather station measuring wind speed, wind direction and horizontal rainfall and a total of 31 WDR gauges measuring WDR on building facades. The spatial distribution of WDR on the building façade has been studied without and with overhangs. The effectiveness of roof overhang is studied with respect to wind speed, wind direction and rainfall intensity. Field measurements show that for the particular climate characterized by long rainy winters with mild wind and rain, the overhang is effective and significantly reduces WDR for this six-story building, especially for areas directly underneath the overhang. The protection increases from the side edge to the center and from the bottom to the top of the façade. As expected, the larger overhang provides greater protection. The relationship between overhang effectiveness and distance from the roofline is quasi-linear with smaller gradient for the larger overhang. The effectiveness of the overhang is highly dependent on wind speed and wind direction-it increases for oblique winds but decreases with the increase of wind speed.
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