A building envelope, in particular a wall, a floor, or a roof of a building with at least two shells spaced some distance apart from one another, which encloses an intermediate space, said space being essentially empty with the exception of weight-bearing and/or construction-engineering elements or being filled at least in sections with porous, open-celled material and sealed from the interior and exterior of the building, wherein controllable sealing means are provided for sealing the intermediate space from the interior and exterior and optionally separated building envelope sections from one other.