Understand the distinction
The building envelope broadly describes the parts separating conditioned spaces from the outside or other spaces. Its exact arrangement depends on the building. A general diagram cannot show every junction or condition in an existing home.
Put it in your home notes
Locate the term in a professional report and ask which elements it refers to there. Retain the drawing or description supplied for your property. Do not infer hidden construction layers from the visible finish or use a decorative illustration as a technical section.