What does an air barrier primarily reduce in a building?

An air barrier primarily functions to reduce drafts and uncontrolled airflow within a building. By creating a continuous and durable barrier, it limits the movement of air between the interior and exterior of a structure. This not only enhances comfort by preventing drafts but also contributes significantly to energy efficiency. When air can flow freely in and out of a building, it can lead to increased energy consumption as heating and cooling systems work harder to maintain desired indoor temperatures.

While reducing energy consumption may seem like a correct choice, it's important to note that the primary role of the air barrier is to prevent unwanted airflow. Reducing drafts directly relates to minimizing the infiltration of outdoor air and the exfiltration of conditioned indoor air. Hence, by effectively controlling this airflow, the air barrier indirectly contributes to energy conservation, but its main purpose is to manage drafts.

In terms of the other options, while air barriers can help mitigate moisture accumulation by controlling airflow that can carry humid air into buildings, their primary role is not moisture management. External noise reduction is typically more influenced by sound insulation and design features rather than air barriers.