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CP-1010: Innovative Passive Ventilation Water-Resistive Barriers—How Do They Work?

By Jablonka/Karagiozis/Straube    Created: 2010/12/13

The issue of solar driven moisture that is associated with water absorptive claddings has often been raised, and it is becoming increasingly relevant as the demand for improved energy efficiency buildings continues to rise. Improved energy efficiency building enclosures generally means an increase in R-value and reduced air leakage, which commonly reduces the drying potential of wall assemblies. Essentially, less energy is available from inside the structure to assist the transport of moisture away from the building enclosure. As energy efficiency requirements are pushing towards zero-energy structures, passive means the sun or wind become more critical approaches for achieving enhanced drying. This paper investigates the hygrothermal performance of wall assemblies with brick veneer cladding as well as manufactured adhered stone veneer with two different types of water resistive barriers. One type is a conventional spunbonded polyolefin-based WRB, and the other type is an innovative three-dimensional dual ventilated sheet. This paper not only shows field-monitored data for both assemblies, but it also explains the building physics involved in both systems. The field performance data is based on one year-long field studies with wood-framed test walls installed on the north and south side of test huts located in Charleston, SC and Waterloo, ON. This paper demonstrates the beneficial effects of passively driven airflow through both solar and wind forces allowing small amounts of air flow to provide a significant increase in drying potential to walls that include dual ventilation water resistive barriers. Results show that the three-dimensional dual ventilated WRB not only provides enhanced drying potential by deploying passive solar energy, but it also provides a control layer against warm-weather inward vapor drives from the absorptive claddings, which have been implicated as reasons for numerous moisture related problems.

 

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