Steel buildings traditionally consist of a structure and a non-load-bearing outer and/or inner envelope. This division into the skin and bones is not efficient constructionally, because each non-load-bearing element represents a form of ballast that demands larger dimensions for the structural members.

Monocoques, in contrast, are a type of building in which an internal linear framework and a load-bearing skin form a structural whole. An analogy exists to the outer shells of insects and crustacea. This highly efficient lightweight form of construction has established itself above all in shipbuilding.