In modern architecture, the vestibule refers to the small space or room between an entrance and the interior of a structure, with a set of inner doors and a set of outer doors. In terms of function, the vestibule serves as an air lock which controls potential heat/air loss by having only one set of doors open at a time. Vestibules were common in ancient Greek temples, where two rows of columns supporting the roof were used at an entrance, creating a distinct area at the entry. The Romans coined the actual word vestibule, which referred to a partially enclosed space between the interior of a house and the street, something like a porch. Vestibules were also used in Christian churches starting in the 5th century.
Typically small and functional, the vestibule can serve many functions such as a mudroom or a place to collect the mail. Architecturally, the vestibule gives us the opportunity to move gradually from outside to inside, easing the transition between public and private spaces.
As heating improved in the mid-20th century, vestibules were no longer needed as the functional air lock, and to include the vestibule as a transition space wasn’t worth the extra cost. Today, it is rare to see a modern home that includes a vestibule, but if you have the space to be creative, you can add one!
(Images via pinterest, apartment therapy, houzz)