Stocorp.com
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| Why are air barriers important? |
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By constructing an airtight building envelope the risk of moisture problems—decay, corrosion, loss of insulation value, mold growth and IAQ (Indoor Air Quality) problems—that can occur because of air leakage and condensation are minimized. At the same time airtight construction is likely to be less capable of drying than “air-porous” construction in the event of water leakage or other unforeseen circumstances that cause water to enter into a wall assembly. The designer then must strive to prevent rain water penetration into the wall assembly, to construct an airtight building envelope assembly of compatible air barrier materials, and to enhance the drying potential of the wall assembly in his/her overall design strategy. When incorporating StoGuard™ spray-on air/moisture barrier materials in wall assemblies, the following considerations are important to effectively control condensation and prevent moisture penetration:
- Air Permeability
- Air Barrier Continuity
- Air Barrier Structural Integrity
- Air Barrier Durability
- Water Penetration Resistance
- Water Vapor Permeability
- Mechanical Ventilation
- Construction Details and Sequencing
- Code Compliance
- Climate
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| Water penetration and StoGuard™ |
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The traditional moisture protection used in wall construction is asphalt saturated felt or kraft waterproof building paper. The terms weather-resistive barrier, moisture barrier, or sheathing membrane are often used to describe these components in wall construction. They are generally installed over sheathing by lapping them shingle style and fastening with nails, screws or staples to the sheathing. Their general purpose in walls is to protect against ingress of incidental water into the building and to protect moisture sensitive components like gypsum sheathing in the event of a breach in the outer wall covering, such as a crack in stucco. Building wraps are often used in place of asphalt felt in wall construction, often with the same perceived purpose. The water resistance, air infiltration resistance, and vapor permeability characteristics of building wraps vary widely, depending on the brand of wrap selected (PHRC Report No. 59, p.8]). StoGuard™ seamless spray-on moisture protection provides a significant improvement over traditional moisture protection and building wraps. In fact, it is more than 10 times more resistant to water penetration than some building wraps and nearly 200 times more resistant to air leakage
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| Water Vapor Permability | | | |
StoGuard™ is water vapor permeable. As a "breathable" water proof air barrier, StoGuard permits water vapor to diffuse through it. This is important for the drying of the wall, should water accumulate in materials during construction or incidental water leakage occur after construction.
Some sheet membranes do not allow water vapor diffusion, which can result in a damp or saturated building assembly. |
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How can a material be both waterproof and vapor permeable? |
Water vapor consists of very small individual water molecules in a gas form. Water vapor molecules will easily flow through pores and openings in a material. More, or larger openings result in more vapor that flows through. Materials that permit the passage of water vapor are termed vapor-permeable. | |  |
Liquid water is cooled water molecules held tightly together via cohesion. The tight cohesive force creates surface tension that draws water into larger round drops. This surface tension allows water to cling to other objects. Surface tension will cause liquid water to bridge the small holes that water vapor can pass through. | |
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 Tech Hotline: Vapor Permeable vs. Waterproof |
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