The enclosure-first approach reduces energy consumption and provides a comfortable indoor environment for the occupants. A key strategy in achieving high-performance buildings is the use of well-insulated assemblies. These assemblies use insulation with minimal thermal bridging to resist heat loss or gain to lower the overall mechanical heating or cooling load. The enclosure components in a highperformance building, e.g., windows and doors, are also thermally efficient to control heat loss and gain. The restriction of air movement (i.e. air leakage through the enclosure) by the air barrier system is one of the most important functions of the building enclosure.

Uncontrolled air leakage results in excessive heat loss that leads to thermal discomfort and energy waste, and can lead to moisture issues within the building enclosure. Besides improving the energy efficiency of the building, an enclosure-first approach can also contribute to better occupant comfort, since the building will allow less uncontrolled airflow and will have warmer interior surfaces and a more uniform indoor air temperature.