What is a common characteristic of a sealed polyethylene air barrier?

A common characteristic of a sealed polyethylene air barrier is that joints in the sheet are sealed to prevent air leakage. This sealing is crucial because it ensures the integrity of the barrier, making it effective at controlling air movement. When a polyethylene air barrier is installed, the connections and overlaps between sheets must be properly sealed using compatible tapes or adhesives. This prevents unwanted air leaks, enhancing the building's energy efficiency and overall performance.

In contrast, allowing moisture to pass through freely would defeat the purpose of an air barrier, which is designed to limit air infiltration and exfiltration. Applying the air barrier externally could expose it to damage and not provide the intended airtight protection that it would have if installed correctly on the interior side of the insulation. Furthermore, a sealed polyethylene air barrier does require sealing and special treatment at its joints in order to function effectively; therefore, suggesting that no sealing is required would not align with standard practices in airtightness testing and building science.