An air barrier is a continuous material or system specifically designed to stop uncontrolled air movement through a building’s envelope, addressing drafts, energy loss, and moisture problems that can occur when air, along with the moisture it carries, moves freely through gaps and penetrations in the wall assembly.
While related to a weather-resistive barrier, an air barrier’s primary function is specifically stopping air movement, whereas a weather-resistive barrier’s main job is blocking liquid water, though some products are engineered to serve both functions simultaneously.
Achieving genuine air barrier continuity requires careful attention to every seam, penetration, and transition throughout the building envelope, since even small gaps can significantly undermine the system’s overall effectiveness.
What Does an Air Barrier Involve?
- A continuous material or system stopping air movement
- Careful sealing at every seam, joint, and penetration
- Integration with the weather-resistive barrier, sometimes combined
- Verification through blower door testing in some projects
Why Is an Air Barrier Important?
Uncontrolled air movement through a building’s envelope contributes significantly to energy loss, comfort problems like drafts, and can also carry moisture into wall cavities where it might condense and cause hidden damage, making effective air sealing a genuinely important factor in both energy efficiency and building durability. This dual impact has increased building science’s emphasis on air barrier continuity in recent years.
Because achieving true air barrier continuity requires attention to details that are easy to overlook, like electrical outlet boxes or plumbing penetrations, more rigorous construction approaches increasingly include blower door testing to verify actual performance rather than assuming visual inspection alone confirms adequate air sealing.
Air Barrier vs. Vapor Barrier
An air barrier specifically stops air movement through the envelope. A vapor barrier specifically blocks moisture movement in vapor form through the air, a related but distinct function addressing a different transport mechanism entirely.