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Watch this short video to meet Jean-François Côté, Director of Standards and Scientific Affairs at Resisto, who will host this live Webinar on Thursday, November 2, which qualifies for one RCI and AIA continuing education hour.
You will learn more about vapor permeable air barriers. Register today!
In the meantime, here is some more information to better understand permeance, critically examining the discussions around PERMs and choosing the right vapor-permeable air barriers for your future projects.
Several factors must be taken into account when selecting an air barrier membrane for a wall design. The main purpose of an air barrier is to prevent air leakage through the building envelope. Uncontrolled air circulation can cause heat loss and high resultant energy costs, not to mention increase the risks of condensation and mould growth in the assembly.
Irrespective of their air leakage rate, permeable air barrier membranes are categorized according to their water-vapor permeance. The degree to which water vapor passes through a wall is specific to each type of air barrier. The diagrams below show the effects of water-vapor diffusion, per type of air barrier, for hot summer weather and cold autumn temperatures. Note that the more permeable an air barrier, the more it allows water-vapor diffusion in the assembly.
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Water-vapor permeance of materials used in an exterior wall assembly has an impact on the drying time of the assembly. Based on hygrothermal simulations, this graph demonstrates the influence of air barrier permeance on the drying time of a wall.
Increasing membrane permeance above 10 US perm only provides marginal benefits to drying. Simulations illustrated* above demonstrate that the drying time of a wall is only 12 days faster when permeance is increased from 10 US perm to 50 US perm. In other words, a membrane that is five times more permeable will not allow the wall to dry five times faster. However, a 50 US perm membrane will allow faster moisture accumulation inside the assembly through inward vapor drive, thereby increasing risk of condensation.
Want to learn more about choosing the right vapor-permeable air barrier?
REGISTER for our free webinar, specially designed for architecture professionals.
In addition, the drying dynamics of any wall assembly will be dictated by the material that has the lowest water vapor permeance. Consequently, the potential benefits of a highly permeable air barrier will often be mitigated by another material that determines the assembly’s drying
Among the permeable air barrier lines available on the market, prefabricated self-adhesive membranes have varying adhesive properties. An effective permeable air barrier must readily adhere to most building surfaces. The REDZONE STICK VP permeable air barrier membrane meets and exceeds this basic specification. In fact, it stands out from the competition thanks to its unmatched adhesive qualities. Moreover, no primer is required for its installation.
Several criteria must be considered when selecting an air barrier. In addition to the above mentioned criteria, other factors are also taken into account, including:
All of these factors complicate the drying of a damp wall. Consequently, it is essential to choose a membrane by considering the wall type in which the membrane will be installed, and not only by membrane permeance.
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