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It all started when someone submitted a proposal to the 1993 NEC to
substitute "Story" for "Floor" in Article 336. An innocent
enough proposal right! After all, how many of us have been doing just that
anyway, using story and floor interchangeably. Well, guess what? Story and Floor
are not interchangeable and, as a matter of dire consequences, the two terms
have led some very significant interpretations. For instance, what happens if a
penthouse is added to a structure with three countable floors . By most building
codes (and there are three in the U.S.) the penthouse would not be a story, but
by the NEC it would be a floor. Therefore, Nonmetallic sheathed (NMB) cable
cannot be used in this structure. Now what happens if a three floor wing is
added to this. Can the three floor wing be wired in NMB cable? No, not unless a
four hour fire wall separates the wing from the part of the structure with four
or more floors. And if there is a four hour fire wall then a separate service is
required for the three floor wing. By the way, the Code making Panel rejected
using story for floor because there are three model building codes in the United
States and each defines Story differently.
Also, the terms floor, story, and level are not interchangeable. A Floor and
a Story are Levels. A Story is a term we should not use, but, by all accounts, a
story is a floor. A level is not a floor if it is the first level and is not for
human habitation and is used only for vehicle parking, storage, or similar use.
Also, the first floor of a building shall be that floor that has 50 percent or
more of the exterior wall surface area level with or above finish grade.
Therefore, a basement designed for human habitation that has 50 percent of its
exterior surface area below finished grade is not a floor but is clearly a level
and may be a story by the applicable building code.
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