Thirteenth floor is a designation of a level of a multi-level building that is often omitted in countries where the number 13 is considered unlucky. Omitting the 13th floor may take a variety of forms; the most common include denoting what would otherwise be considered the thirteenth floor as level 14, giving the thirteenth floor an alternate designation such as "12A" or "M" (the thirteenth letter of the Latin alphabet), or closing the 13th floor to public occupancy or access (e.g., by designating it as a mechanical floor).
Reasons for omitting a thirteenth floor include triskaidekaphobia on the part of the building's owner or builder, or a desire by the building owner or landlord to prevent problems that may arise with superstitious tenants, occupants, or customers. Based on an internal review of records, Dilip Rangnekar of Otis Elevators estimates that 85% of the buildings with elevators did not have a floor named the 13th floor. Future building designers, fearing a fire on the 13th floor, or fearing tenants' superstitions about the rumor, decided to omit having a 13th floor listed on their elevator numbering. This practice became commonplace, and eventually found its way into mainstream culture and building design.
The origin of skipping the thirteenth floor when installing elevators is not known. However during the advent of early skyscrapers, New York architectural critics warned developers not to exceed the height of the 13th floor. These critics insisted buildings rising above the 13th floor (125 feet) would lead to increased street congestion, ominous shadows and lower property values. Nevertheless, in a work published in 1939, sociologist Otto Neurath compared the use of money in an economy, which he saw as unnecessary, to the superstition of not installing the thirteenth floor: merely a social convention.
How it is done 
Most commonly, it is skipped altogether. The floor numbered 14 is in fact the thirteenth floor, and 13 is skipped altogether on the elevator console and therefore all numbers above 13 are then out of sequence. Any calculations involving the height of a building based on the height of a floor will take this into account.
12A and 14A 
Sometimes the floor is simply renumbered as 12A on 12 and/or 12B on 13; this does not affect the numbers of the higher floors. Likewise, 14A and 14B may also be used for 13 and 14, respectively.
Special designations 
Other buildings will often use names for certain floors to avoid giving a floor on the building the number 13 designation. One such example is the Radisson Hotel in Winnipeg, Manitoba, where the 13th floor is called the Pool floor. Another example is the Sheraton on the Falls in Niagara Falls, Ontario, where the 13th floor consists solely of a restaurant.
Letter M 
Because the letter M is the 13th letter in the Latin alphabet, some people may use a letter M as a substitute for the floor numbered 13, such as 12, M, 14, and so forth. In Richmond, Virginia, the Monroe Park Towers has a 13th floor, but it is used for mechanical equipment and is only accessible from the freight elevator or the stairs. The M designation on the elevator buttons of the freight elevator can also be construed as meaning the "Mechanical" level in this particular building, or as a "Mezzanine" level.
Split-level apartments 
Sometimes, a tenement block will contain split-level apartments where the units themselves contain internal staircases and the main elevators for the building therefore do not stop on every floor. One example is Princess Towers in Kingston, Ontario, which has 16½ stories excluding the roof-top. The elevators stop at B (basement), G (ground), 3, 6, 9, 12 and 15th floors only. In this case, the unmarked 11th and 13th floors are accessed within units on the marked 12th floor.
Similarly, new buildings in some parts of China omit the fourth, fourteenth, twenty-fourth, etc. floors, as the word "four" (Hanzi: 四) sounds like "death" (死 – pronounced "sì" and "sǐ", respectively) in Mandarin, the predominant language for the country, and most other Chinese languages. A small number of buildings also follow the American tradition of omitting the thirteenth floor, with the fifteenth floor immediately following the twelfth.
In South Korea, buildings tend to include the fourth floor in spite of similar pronunciation issues in the Korean language, though some newer buildings may substitute the letter F in the place of the number 4.
Thirteenth room 
Highway 13 
Likewise, a U.S. Route 666 in the United States Numbered Routes system, known as the "Devil's Highway", was renumbered to US 491 (however, this happened only after its parent, the famous US 66, was decommissioned).
Conspiracy theory 
Some conspiracy theorists have suggested that the thirteenth floor in government buildings is not really missing, but actually contains top-secret governmental departments, or more generally that it is proof of something sinister or clandestine going on. This implication is often carried over, implicitly or explicitly, into popular culture; for example in:
- the films The Thirteenth Floor, Nightmare on the 13th Floor, and 1408
- the hidden research and development labs of Network 23 in the television program Max Headroom
- the top-secret research and development division of The Hitchhiker's Guide to the Galaxy in the fifth book of the series, Mostly Harmless
- the computer game Floor 13 by Virgin Interactive
- the sci-fi comedy Red Dwarf where "floor 13" referred to a secret brig which was several decks high.
- the book Company by Max Barry
- the Superman story in Action Comics #448 (June 1975) featured a secret thirteenth floor used to teleport alien tourists from another planet to visit Earth.
- The "Night of Owls" storyline in Batman features the thirteenth floors of Gotham's buildings being used as bases by the assassins of a secret society that has ruled Gotham for generations.
- the level "The 13th Floor" in the computer game Tomb Raider: Chronicles
- the episode "Grey 17 Is Missing" of the TV series Babylon 5 has a similar theme of a "missing" floor number actually containing a hidden floor with dark secrets.
- The psychedelic rock band The 13th Floor Elevators
- The Rockford Files episode "Sticks and Stones May Break Your Bones, But Waterbury Will Bury You".
It is widely believed that Canary Wharf's One Canada Square houses a physical plant room on its level 13 but this is just another example of undeserved notoriety on the part of the 13th floor. One Canada Square's plant areas are in its basements (Levels B3 to M1) and above Level 50 (Level M2). The floor directly above level 12 is level 14.
See also 
- Fleischman, Sid (2007-08-19). "The 13th Floor: A Ghost Story". The Washington Post Company. Retrieved 2008-07-26.
- Perkins, Broderick (2002-09-13). "Bottom Line Conjures Up Realty's Fear Of 13". Realty Times. Retrieved 2008-04-14.
- Glaeser, Edward (2011-05-24). "Triumph of the City". Critical Environmentalism. Retrieved 2011-06-02.
- William Kaszynski (May 28, 2003). Route 66: Images of America's Main Street. ISBN 9780786415533.
- Cameron Bevers. "The King's Highway (Ontario)".