In New York around lower Manhattan I saw some storefronts with these boxed doors outside.
What are they called and what is their function?

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  • 6
    Many other towns have these built right into the building. In the suburban midwest you must always go through 2 doors to get into a Mcdonalds, Starbucks, Wendys, Trader Joes, etc. Apr 6 '19 at 2:20
  • The same in Sweden. In some buildings, the inner door won't open before the outer door is closed (in particular with automatic sliding doors).
    – gerrit
    Apr 6 '19 at 7:28
  • An interesting point is, I've never known what these are called! People just call them "the double door thingy that you add on in winter".
    – Fattie
    Apr 6 '19 at 23:00

That is a sidewalk vestibule. The idea is to have an extra door between the building's interior and the outside, so as to reduce the amount of air exchanged when people go in and out. In winter, warm air stays inside and cold air stays outside, reducing the building's heating costs and avoiding uncomfortable drafts for diners sitting near the door.

You could also have a vestibule inside the restaurant's regular doors, but that would occupy valuable floor space, and would be useless during warmer seasons. The temporary vestibule can be put up in winter and taken down in summer.

  • 11
    In general, perhaps. In New York City, not so much - as the article points out, they are used primarily in winter, when flying insects are not found outdoors. Apr 6 '19 at 2:50
  • 2
    For heating/air conditioning, as stated, is the usual purpose. However, I have been in a couple of places where staff could lock the outer door remotely, and lock the inner while a thief is trying the outer. Temporary jail till the police arrive!
    – WGroleau
    Apr 6 '19 at 10:14
  • 6
    @WGroleau In that case, it's called a mantrap and is usually built much more sturdily. Apr 6 '19 at 20:01
  • 2
    @Tetsujin NYC has plenty of bureaucracy, and I'm sure that there are fire rules for how these must be constructed (e.g., the external door still opens outward into the street, etc.). Apr 6 '19 at 20:02
  • 8
    As the article points out, it is surprising the NYC allows them at all just from the standpoint of sidewalk obstructions. Most cities don't allow businesses to just expand their entryway into the public sidewalk, and NYC does have plenty of bureaucracy. This just happens to be something they don't care about. Apr 6 '19 at 22:06

While I do not know what they are called, their purpose is to keep heat inside by creating an extra air chamber between the inside which is heated and the outside. These are usually removed in the warmer months.

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