1 Research Engineer, Building Engineering Group, Civil Engineering Department, University of Waterloo, Waterloo, Ontario, Canada, N2L 3GI
2 Professor, Depts of Civil and Environmental Engineering and Architectural Engineering, Pennsylvania State University, University Park, PA, USA
ABSTRACT
Vent openings in masonry veneers are commonly specified in modern Canadian wall systems. Several different products are available to screen these vent openings from insects and direct penetration by driving rain. While venting is considered good practise, there is little engineering basis for the size and spacing of vent openings.
With the support of a number of research partners, the role of venting in masonry veneer walls has been investigated. The importance of venting to pressure moderation and the control of rainwater, the removal of water vapour from behind the relatively vapour impermeable masonry veneer screen, and to the potential for ventilation drying were studied through a combination of theory, laboratory testing, and field monitoring.
Both theory and testing have confirmed the importance of sufficient venting. The four vent inserts tested in our program all restricted airflow to a very high degree; in fact, they practically negated most of the benefits of venting. It was shown that ventilation could remove significant quantities of water from both the back of the veneer and from the backup wall so long as proper design and construction were provided. Field measurements confirmed that sufficient pressures act over most faces of a building for most of the time to drive ventilation air flow. It was also demonstrated that vent area and vent location are important variables that must be considered in design if the performance and durability benefits of venting and ventilation are to be realised in service.
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