Assessing the Moisture Load in a Vinyl-Clad Wall Assembly through Watertightness Tests

The moisture load in wall assemblies is typically considered as 1% of the Wind Driving Rain (WDR) load that is deposited on the surface of wall assemblies as specified in the ASHRAE-160 standard whereas this ratio has been shown to be inaccurate as compared to results derived from several watertightness tests. Accurate assessment of moisture loads arising from WDR can be obtained through the watertightness test during which different levels of WDR intensities and Driving Rain Wind Pressures (DRWPs) are applied to a test specimen and water that penetrates wall assembly can thus be quantified. Although many previous studies have included watertightness tests, only a few of these have attempted to correlate the moisture loads to WDR conditions as may occur in specific locations within a country. To improve the assessment of moisture loads for a vinyl-clad wall assembly, a wall test specimen was tested following a test protocol based on local climate data using National Research Council of Canada’s Dynamic Wind and Wall Testing Facility (DWTF). The use of this test protocol permitted quantifying the moisture load in the vinyl wall assembly when subjected to several different simulated WDR conditions. The moisture load was formulated as a function of the WDR intensity and DRWP which thereafter allowed evaluating the moisture load based on a given climate’s hourly rainfall intensity and wind velocity. Such work is particularly relevant considering that the intensity, duration and frequency of WDR events across Canada will in some regions increase due to the effects of climate change.

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