In BPI terminology, what does the "envelope" of a building refer to?

The term "envelope" in BPI terminology refers to the outer shell of the building. This includes all the elements that separate the conditioned space from the unconditioned space outside, encompassing walls, roof, windows, and doors. The envelope plays a crucial role in the overall energy efficiency of a building, impacting heat loss and gain, ventilation, and moisture control.

Understanding this concept is vital for anyone involved in building performance evaluation, as it helps in identifying air leaks, insulation efficiency, and overall thermal performance. By focusing on the envelope, professionals can implement measures to enhance energy efficiency, comfort, and indoor air quality.

The other choices, while important components of a building, do not define the envelope as recognized in BPI terminology. The inner walls are part of the interior and do not contribute to the thermal boundary in the same way the envelope does. The HVAC system is concerned with heating and cooling rather than the physical structure that retains conditioned air. The foundation supports the building's weight but is not typically included in the concept of the envelope itself.