Air and Weather Barrier

Cracks, gaps, and other leakage points in walls can lead to water and air entry into a wall cavity through wicking, gravity, and wind. An air and weather barrier is part of a wall assembly that prevents moisture, rain, and wind from entering critical areas in walls and roofs.

Air and weather barriers are becoming increasingly important in controlling common issues caused by weather-related moisture penetration and buildup, including:

• Mold
• Wood rot
• Metal corrosion
• A decline in the R-value of insulation material

Air and weather barriers are placed on the wall assembly's interior or exterior side, dictated by the local climate.

1. Air and weather barriers are placed on the interior wall in regions where heating occurs most often to prevent moisture buildup.
2. Air and weather barriers are placed on the wall's exterior side in areas where cooling frequently occurs.

Not all barriers are the same. Air and weather barriers have a permeability rating which describes the rate at which water vapor transfers through the barrier. 1.0 US perm = 1.0 grain of water vapor/square-foot/hour/inch of mercury, and barrier's with less than 1 perm are considered impermeable.</p><p>Many jurisdictions now require new construction to include air barriers. When selecting the best air and weather barrier for your home, consult local code requirements and seek guidance from a trusted local contractor. To ensure you've done your research, here's a list:

• Local building code requirements
• Choose the proper barrier for your climate
• Select a barrier manufactured to meet your intended useIs the barrier compatible with other building materials
• Review performance tests

Once you've selected the appropriate barrier, it's equally important to install the barrier based on the manufacturer's directions. Most failures arise from poor installation.

A properly installed barrier helps your home control humidity and indoor air quality and extends the structure's lifespan, which could be impacted by continuous exposure to air and moisture.

Felt paper, commonly referred to as black tar paper, was the first commercially available weather barrier. Due to felt's ability to tear easily, modern barriers are made from extremely fine, high-density polyethylene fibers, which are flexible and offer better air, water, and weather-related properties.