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What Is 'Reverse Vapor Drive' ?
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Image shows poorly ventilated wall with condensation. |
Reverse vapor drive' or 'inward solar vapor drive
' is used to describe the inward vapor movement due to solar heating of an absorptive
cladding such as brick veneer, stucco, and manufactured stone.
In the 1990's air-conditioned homes with poorly ventilated brick veneer were showing signs of condensation on the interior vapor barriers during the summer months. In the investigations that followed it was clear that the summer time condensation was in part due to reverse vapor drive.
Mitigating Vapor Pressure 'Push'
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| Figure 1. Rendering of Vapor Pressure Push (2017) |
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Figure 1 shows the common yet problematic solution to prevent reverse vapor drive is the installation of an exterior vapor barrier.
Unfortunately, this seals
out vapor, but seals
in
any trapped moisture.
Preventing Reverse Vapor Drive with Rain Screen Design
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Figure 2. Rendering of Ventilated Wall System (2017.) |
A ventilated wall system-sometimes referred as a rain scre
e
n-provides a drainage and venting cavity for the wall system
(Figure 2.)
VaproShield's Installation Best Practices requires a rain screen or ventilated cladding design that 'vents off' the resulting vapor pressure when present. This practice prevents reverse vapor drive and allows effective drying in both directions of the wall system.
Review the complete Ribbit Resource on Reverse Vapor Drive on our website.
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