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Appendix A: Weather Resistant Barriers

Rear ventilated facade systems and WRB overview
Conventional, single line barrier systems function by attempting to completely seal the building and create a single, universal layer of protection against every force. This barrier is prone to be unsuccessful as the integrity and effectiveness of this system rely heavily on the installation. Even in systems utilizing a secondary gutter backup system, the long term integrity lies with the resilience of the internal seals and the quality of workmanship at the time of installation.

Unlike conventional wall design, rear ventilated facade systems function by deflecting most precipitation, while the limited amount of moisture that enters the ventilated cavity may dry easily. It is important to note that NorthClad™ rainscreen panels and their respective substrates do not provide a waterproof barrier and thus must be used in tandem with a weather impenetrable membrane. Although water will enter the ventilated cavity with the free flow of air through the system, it will quickly be dried by the constant ventilation. These system are designed so that the open back cavity will mitigate the problems created by trapped water such as corrosion and mold, but only if an effective element barrier is also employed. (e.g. Henry® Air-Bloc® 33)

Henry® Air-Bloc® 33, an air and watertight barrier which allows for the passage of water vapor, is one product that may be used as an element barrier to accompany a NorthClad™ rainscreen system. Air-Bloc® 33 may be applied with a trowel or by spray, and must be used with a transitional membrane such as Blueskin® in order to adequately prevent moisture from penetrating the system. Any technical questions regarding the Air-Bloc® 33 should be directed to Henry®.

Recommended WRB manufacturers:

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