Which of the following best describes an air barrier system?

An air barrier system is fundamentally designed to control air movement between the conditioned interior environment and the unconditioned exterior environment. This system functions as a continuous barrier that effectively restricts airflow, thus preventing unwanted air exchange, which can lead to energy loss, moisture infiltration, and potential damage to building materials.

By creating a sealed environment, an efficient air barrier system helps to maintain the building's thermal integrity and improve energy efficiency. This means that when properly installed, the barrier prevents air from leaking in or out, which is critically important for HVAC performance and overall indoor air quality.

In contrast, the other options do not provide the necessary function of controlling airflow: ventilation ducts facilitate airflow rather than restrict it; open windows allow for air exchange instead of preventing it; and a decorative building facade serves aesthetic purposes without addressing air infiltration or exfiltration issues. Thus, the description of an air barrier system as a continuous barrier to prevent air exchange is the most accurate and reflects its essential purpose within building design.