Which component is NOT part of the building envelope?

The HVAC system is not considered part of the building envelope because it serves a different function within the structure. The building envelope comprises all the physical barriers that separate the indoor environment from the outdoor environment, directly influencing energy efficiency, insulation, and moisture control. This includes the roof, walls, and windows, which are integral to the building's thermal performance and protection against the elements.

While the HVAC system is crucial for regulating temperature and air quality inside the building, it operates independently of the building envelope. Its components, such as furnaces, air conditioners, and ducts, are responsible for heating, cooling, and ventilating spaces, rather than forming the physical barrier that impacts energy flow and environmental separation. Understanding the distinction between these systems is essential for evaluating building performance and energy efficiency strategies.