from the 2021 IBC code illustrated
STORY ABOVE GRADE PLANE. Throughout the code, the number of qualifying stories in
a building is a contributing factor to the proper application of the provisions. As an example,
a building’s allowable types of construction are based partly on the limits on height in stories
placed on various occupancy groups. In this case, the code is limiting construction type based
on the number of stories above grade plane. The code defines a story above grade plane as any
story having its finished floor surface entirely above grade plane. However, floor levels partially
below the grade at the building’s exterior may also fall under this terminology. The critical part
of the definition involves whether or not a floor level located partially below grade is to be con-sidered
a story above grade plane. There are two additional criteria that are important to the
determination if a given floor level is to be considered a story above grade plane:
1. If the finished floor level above the level under consideration is more than 6 feet
(1,829 mm) above the grade plane as defined in Section 202, the level under consider-ation
is a story above grade plane, or
2. If the finished floor level above the level under consideration is more than 12 feet
(3,658 mm) above the finished ground level at any point, the floor level under consid-eration
shall be considered a story above grade plane.
Where either one of these two conditions exists, the level under consideration is also con-sidered
a story above grade plane.
Conversely, if the finished floor level above the level under consideration is 6 feet (1,829 mm)
or less above the grade plane, and does not exceed 12 feet (3,658 mm) at any point, the floor level
under consideration is not considered a story above grade plane. By definition, it is regulated
as a basement. Figures 202-20 and 202-21 illustrate the definitions of “story,” “basement,” and
“story above grade plane.”
Although the criteria for establishing the first story above grade plane in Item 2 indicates
that such a condition occurs where the 12-foot (3,658-mm) limitation is exceeded, the applica-tion
of this provision is not that simple. It is not the intent of the code to classify a story that is
completely below grade except for a small entrance ramp or loading dock as a story above grade
plane, provided there is no adverse effect on fire department access and staging. An analysis of
the impact of such limited elevation differences is necessary to more appropriately apply the
code’s intended result.
