"A building envelope is the physical separator between the conditioned and unconditioned environment of a building including the resistance to air, water, heat, light, and noise transfer."
Wikipedia,"Building Envelope" 2019
The building envelope is all of the elements of the outer shell that maintain a dry, heated, or cooled indoor environment and facilitate its climate control. Building envelope design is a specialized area of architectural and engineering practice that draws from all areas of building science and indoor climate control.
Syed, Asif. Advanced building technologies for sustainability. Hoboken, N.J.: John Wiley & Sons, Inc., 2012. 115. Print.
The many functions of the building envelope can be separated into three categories:
Support (to resist and transfer structural and dynamic loads)
Control (the flow of matter and energy of all types)
Finish (to meet desired aesthetics on the inside and outside)
The control function is at the core of good performance, and in practice focuses, in order of importance, on rain control, air control, heat control, and vapor control.
Straube, J.F., Burnett, E.F.P. Building Science for Building Enclosures. Building Science Press, Westford, 2005.
Water and water vapor control