This barrier between indoors and outdoors is important with regards to ventilation and insulation of a conditioned space. A “tighter” envelope (i.e. one with fewer gaps through which air can flow) more effectively keeps conditioned air in, reducing the load on the HVAC system, and therefore increasing the efficiency at which it operates. Similarly, insulation helps slow the conduction of heat through walls. Windows are generally less efficient than walls, and are also a common site for air infiltration. Energy-efficient windows can save 7-15% of residential energy. However, good windows are expensive, and are generally less cost-effective than other efficiency measures. Improving the efficiency of the building envelope is generally a low-cost, high-return method for increasing efficiency in buildings.
The building envelope is part of a building's commissioning. Commissioning is a quality assurance process for new construction projects that begins with pre-design and continues through design, construction, and early operation. Commissioning is intended to ensure that building systems and equipment have been designed, installed, and tested to perform in accordance with the design intent. .
Retrocommissioning, or “existing building commissioning,” is a systematic process for identifying and implementing operational and maintenance improvements in a building to ensure continued good performance over time. The intent of the process is to optimize the performance of building subsystems as well as how they function together. Retrocommissioning focuses on operations and maintenance improvements and diagnostic testing, although needed capital improvements may be identified and recommended through the process.