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About Vestibules

The word Vestibules comes from the Latin word Vestibulum which means entrance court. In ancient Rome homes generally had a small court between the street and the house. Modern vestibules are small indoor hallways that connects the exterior door to a large room. In modern homes vestibules generally connect the main entrance to the living room. However, in commercial buildings vestibules can connect one or more main entrances to a lobby, a reception hall, a store, a restaurant, or any place where the public does business.

There several ways vestibules are used. In private homes they are used as a place to leave outdoor clothes and footwear. They can be used as rooms where visitors wait for their contact person. They are used as mudrooms. But almost always they used to conserve energy and prevent drafts. Commercially, that is the essential reason. By having only one of the doors in a vestibule open at a time, it saves considerably on both heating and air conditioning bills.  

Banks often have ATM vestibules. That is where they keep the automatic teller machines, where they can be accessible for 24/7. ATM vestibules may have a second set of doors into the bank or they may not. If they don’t, they usually require a cardkey to unlock.

Some Vestibule Requirements in Commercial Buildings.

A number of agencies have put out codes for vestibules to make sure they do what they are supposed to.  

IECC (International Energy Conservation Code)

  • The IECC requires commercial builders to install vestibules on all primary entrance doors that lead to indoor spaces of 3000 square feet or greater.  All areas that are not closed off from the entrance by doors or walls are included. The exceptions to this rule are buildings that are in climate zones 1 and 2, utility doors that are not intended for the public, doors that open into living space, like hotel doors, and revolving doors which already function as energy conservation tools.
  • If vestibules protrude from the exterior of the building the walls must meet the requirements for exterior walls. If they are built into the conditioned space, the walls must meet the requirements for interior walls.
  • All doors leading into and out of the vestibule should have closers.
  • Vestibules are to be designed so that the exterior and interior doors do not need to be open at the same time. There should be at least 48 inches of space between the swing clearances of all doors. In the diagram below only one of the doors swings into the vestibule. The 48 inches are counted from the edge of the clearance on the left to the edge of the door frames on the right. 


ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers)

  • Besides the above requirements, instead of the 48 inch between door swings, ASHRAE requires a minimum distance of 7 feet between closed interior and exterior vestibule doors which is about the same as clearing 48 inches, depending on the size of the door.

ASHRAE exceptions for the 3000 square foot rule is …

  • Buildings in climate zones 3 and 4 that are less than 4 stories with an area of less than 10,000 sq feet.
  • Buildings in climate zones 5, 6, 7, 8 less than 1,000 sq ft in area.

ANSI (American National Standards Institute)

  • ANSI requires vestibules to be a minimum of 60” in width making it possible for wheelchairs to turn around in the vestibule.
  • They also require revolving doors to have a side-hinged swing door on the same wall within 10 feet of the revolving door.

Besides the IECC, ASHRAE, and ANSI, vestibules must also comply with ICC’s (International Code Council) International Building Code for egress and accessibility.

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