According to the "NYC Department of Buildings (DOB) Quick Reference Guide For All DOB Temporary Special Event Filings," it appears that temporary tents do not need special permits in order to be constructed.
Here is the relevant section from the reference guide linked above (which I found thanks to Daniel Sieradski):
Criteria for Requiring a DOB Work Permit(s):
1. Platforms, Stages, Trusses and Bleachers:
a) Temporary platforms, bleachers, reviewing stands, outdoor bandstands and
similar miscellaneous structures that cover an area of 120 square feet or
more and over two (2) feet in height or that will be in place for 30 days or
more require a Work Permit (i.e. press riser, camera platform, scaffolding,
etc.).
b) Pre-fabricated structures on wheels do not require a DOB Work Permit - “on
wheels” consists of any stage/riser/bleacher that is pre-assembled and
pre-fabricated with wheels, (i.e. Wenger wagon stage, Parks bleachers, etc.)
c) Any truss that is higher than10 feet requires a DOB Work Permit. A truss is a
support structure with two vertical and one horizontal pieces used in the
supporting of objects (i.e. lighting trusses, start/finish trusses, etc.)
2. Tents and Canopies:
a) Any tent or canopy that is more than 400 gross square feet or will be in
place for more than 30 days requires a Work Permit.
According to the criteria above, a standard tent which stands less than 30 days does not technically need a special event or building permit from the City of New York for a "special event filing" on privately-owned land.
This is important, for Zuccotti Park is indeed privately-owned land which is legally open to the public – in a real estate deal with the city, Brookfield (owners of Zuccotti Park) allowed the land to be designated for public access in return for zoning considerations.
Which means that New York could theoretically look like this:
The view from Occupy Boston.
Now, does this mean confrontations with the NYPD would not happen over such structures? Absolutely not. The NYPD makes nightly sweeps of the park to ensure that structures have not been erected, ostensibly at the behest of Brookfield (though this remains a bit ambiguous).
However, unless there are other applicable codes of which I don't know about, I believe it's time for some tents to pop up at Occupy Wall Street as winter approaches.
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Author's Note: A few have suggested in the comments that tents, or "camping," would be forbidden in Zuccotti Park due to NYC parks regulations.
However, given that Zuccotti is privately-owned land which is legally open to the public, this is not immediately the case. If anyone can find a code which overrides the one cited in this post, please @ mention me in a Tweet (@David_EHG).