Product Brochure

10
Additional Considerations
Cladding Type — Moisture-retaining Claddings
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such as brick, stucco, wood, fiber cement or stone, which are also increasingly prevalent in commercial spaces.
These moisture-retaining claddings can worsen moisture challenges in the cavity presented by mixed-humid
climates. They have the potential to release their moisture into the structure, creating an inward vapor drive that didn’t
exist in vinyl cladded assemblies. This can result in more opportunities for problematic condensation with the need
dry out to the interior of the building.
Solar heat drives moisture into building materials; this is especially true in the case of moisture storage claddings
which can absorb and retain large amounts of moisture. The sun comes out, creating a vapor pressure at the outside
of the wall and driving moisture inward into the lower-pressured building assembly. Since it’s nearly impossible to
prevent moisture from entering 100% of the time, using a smart vapor retarder allows water to escape from building
assemblies as water vapor, which permits the assemblies to dry towards the inside of the wall.
The Moisture Sandwich
Many areas of the country are beginning to install exterior insulation. Exterior insulation will help increase your
wall’s R-value, decrease thermal bridging and reduce the walls permeance level. XPS has a permeance level of 1.0.
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now you have all these factors in place: moisture-retentive cladding (fiber cement/brick/stucco), exterior insulation
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
depending on paint. This common assembly creates a moisture sandwich: moisture will get into the wall and be
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Drywall (depending on paint) 3 – 35 perms
Unfaced batts with poly
< 0.1 perm
OSB sheathing Approximately 2 perms
Housewrap (water-resistive barrier) 5 – 50 perms
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polystyrene insulation (XPS)
< 1 perm
Moisture-retentive cladding
(fiber cement/brick/stucco)
Vapor permeable/
moisture retentive
Vapor permeance ratings
Any material with a perm rating of 1 or below is considered a vapor retarder: