A superior exterior wall vapor barrier must prevent both vapor diffusion and air flow (and the moisture attached to it) from infiltrating a building envelope. Furthermore, a high-performing vapor barrier, like Barricade Building Wrap, is semi-permeable, which ensures the evaporation of moisture within a wall system.
Many exterior wall vapor barriers only stop vapor diffusion, but not air flow, through building materials. Allowing airflow is a problem because moisture transferred by air flow is 50 to 100 times more than that carried by vapor diffusion.
Moreover, these vapor barriers are not sufficiently permeable, so the moisture that enters the wall system through air flow may not escape. Incomplete drying within the building enclosure can cause mold and rot, which is unhealthy to the occupants of a building and can damage the integrity of the structure. A 2018 study found that because the vapor barrier only prevented vapor diffusion, they did not find major changes in the moisture content of the wall system.
Because of the moisture associated with air movement, the best vapor barrier systems must include air-resistance and vapor permeability.
It is essential that vapor barriers stop air-transported moisture, either by conduction, convection, or radiation, from infiltrating a wall system. If warm vapor touches the cold interior walls, the vapor will turn to liquid by condensation.
The permeability for a superior wall vapor barrier ensures evaporation of the moisture within the wall assembly. Permeability (perm) is a wall system’s ability to dry and drain the moisture in at least one direction; however, two directions are better. Water can intrude a wall assembly in many ways: from rain, through conduction, convection, radiation, and from the inside of the structure if the HVAC system does not properly remove the moisture. Therefore, moisture vapor permeability of a vapor barrier is critical so the moisture can escape and not get trapped in the wall assembly.
The need for a vapor barrier material on the exterior of a building or home is dependent on the climate zone. The 2018 International Residential Code R702.7 and the 2018 International Building Code 1404.3 mandate Class I or II vapor retarders and barriers on the interior of a wall frame in climate zones Marine 4 through 8.
Vapor barriers prevent vapor diffusion, while vapor retarders only slow vapor diffusion. The desiccant method of ASTM E 96 determines the vapor retarder (barrier) class by measuring a product’s ability to restrict the amount of moisture that flows through it.
Barricade Building Wrap is a superior exterior wall vapor barrier that provides a continuous air barrier that covers the whole building envelope. Barricade Building Wrap acts as a vapor barrier because it resists moisture while allowing humidity to escape from the interior wall system, which is of particular importance in hot and humid climates. Notably, Barricade Building Wrap is durable over the lifetime of the building and has the strength and stiffness to combat the forces that act on it during and after construction.
Barricade Building Wrap is an effective air and vapor barrier that is continuous, permeable, and durable. Unlike impermeable vapor barriers that only control vapor diffusion, Barricade Building Wrap resists moisture while permitting humidity to escape from interior wall systems. Please visit Barricade® for more information on superior vapor barriers.