Surrounding and protecting a primary building structure is the building envelope.  Consisting of all exterior finishes, the building envelope must function properly to resist moisture intrusion into the concealed areas of the building exterior (wall and roof cavities), while also ensuring that energy consumption is minimized by limiting heat  loss from the occupied interior spaces.  The interaction of building envelope components can be complicated and intricate.  Failure of the building envelope can lead to the primary structure being compromised, and can result in health concerns for the building occupants.