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Is a basement always a story?

Simonsays

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Mar 2, 2010
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Is a basement always considered a story? This isn't about height so don't start talking about grade planes.

Consider this image: a single story (15 feet above grade) over a basement and a sub-basement. Isn't this a three story building?

And if the above example is a three story building, it can't be an unlimited area building under 507.
 

gbhammer

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Seems like it could be a two story with a basement, and may be able to be unlimited if it is a B, F, M, or S use.
 

imhotep

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Aug 3, 2011
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Washington State
Simonsays said:
Is a basement always considered a story? This isn't about height so don't start talking about grade planes.Consider this image: a single story (15 feet above grade) over a basement and a sub-basement. Isn't this a three story building?

And if the above example is a three story building, it can't be an unlimited area building under 507.
Reading IBC 2009 definitions I conclude that basements are merely a type of story. 507.4 is quite specific: Area of a building with no more than two stories above grade plane shall not be limited. I think you do have to consider grade planes.

STORY. That portion of a building included between the upper surface of a floor and the upper surface of the floor or roof next above (also see "Basement," "Mezzanine" and Section 502.1). It is measured as the vertical distance from top to top of two successive tiers of beams or finished floor surfaces and, for the topmost story, from the top of the floor finish to the top of the ceiling joists or, where there is not a ceiling, to the top of the roof rafters. BASEMENT. A story that is not a story above grade plane (see "Story above grade plane" in Section 202).

STORY ABOVE GRADE PLANE. Any story having its finished floor surface entirely above grade plane, or in which the finished surface of the floor next above is:

1. More than 6 feet (1829 mm) above grade plane; or

2. More than 12 feet (3658 mm) above the finished ground level at any point.
 

TJacobs

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Simonsays said:
Is a basement always considered a story? This isn't about height so don't start talking about grade planes.Consider this image: a single story (15 feet above grade) over a basement and a sub-basement. Isn't this a three story building?

And if the above example is a three story building, it can't be an unlimited area building under 507.
Yes, a basement is considered a story, either above or below grade, which is all about grade planes.
 

DwightB

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Apr 13, 2010
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Joplin, MO
The Basin Park Hotel has at least 4 levels with walk-out on grade, maybe 5. I think only the top floor is entirely above grade plan. Are the other levels all basements (below grade plan at some point on the perimeter?)
 

steveray

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Let me clarify....(my position)....if it contains no habitable or useable space, it is not a basement and not a story.....The IBC definition of basement gives no parameters for when the basement line is drawn, just below grade.....3' tall, 6' tall,8' tall....if it is not useable, I would not consider it a story, or a basement....
 

TJacobs

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Notice that the definition of a basement in the 2006 IBC is dependent on the location of the finished floor above.

2006 IBC Section 202:

STORY. That portion of a building included between the upper surface of a floor and the upper surface of the floor or roof next above (also see “Mezzanine” and Section 502.1). It is measured as the vertical distance from top to top of two successive tiers of beams or finished floor surfaces and, for the topmost story, from the top of the floor finish to the top of the ceiling joists or, where there is not a ceiling, to the top of the roof rafters.

STORY ABOVE GRADE PLANE. Any story having its finished floor surface entirely above grade plane, except that a basement shall be considered as a story above grade plane where the finished surface of the floor above the basement is:

1. More than 6 feet (1829 mm) above grade plane; or

2. More than 12 feet (3658 mm) above the finished ground level at any point.

2006 IBC Section 502.1:

BASEMENT. That portion of a building that is partly or completely below grade plane (see “Story above grade plane” in Section 202). A basement shall be considered as a story above grade plane where the finished surface of the floor above the basement is:

1. More than 6 feet (1829 mm) above grade plane; or

2. More than 12 feet (3658 mm) above the finished ground level at any point.



GRADE PLANE. A reference plane representing the average of finished ground level adjoining the building at exterior walls. Where the finished ground level slopes away from the exterior walls, the reference plane shall be established by the lowest points within the area between the building and the lot line or, where the lot line is more than 6 feet (1829 mm) from the building, between the building and a point 6 feet (1829 mm) from the building.

HEIGHT, BUILDING. The vertical distance from grade plane to the average height of the highest roof surface.

HEIGHT, STORY. The vertical distance from top to top of two successive finished floor surfaces; and, for the topmost story, from the top of the floor finish to the top of the ceiling joists or, where there is not a ceiling, to the top of the roof rafters.

:popcorn
 

steveray

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TJacobs said:
Notice that the definition of a basement in the 2006 IBC is dependent on the location of the finished floor above.2006 IBC Section 202:

STORY. That portion of a building included between the upper surface of a floor and the upper surface of the floor or roof next above (also see “Mezzanine” and Section 502.1). It is measured as the vertical distance from top to top of two successive tiers of beams or finished floor surfaces and, for the topmost story, from the top of the floor finish to the top of the ceiling joists or, where there is not a ceiling, to the top of the roof rafters.

STORY ABOVE GRADE PLANE. Any story having its finished floor surface entirely above grade plane, except that a basement shall be considered as a story above grade plane where the finished surface of the floor above the basement is:

1. More than 6 feet (1829 mm) above grade plane; or

2. More than 12 feet (3658 mm) above the finished ground level at any point.

2006 IBC Section 502.1:

BASEMENT. That portion of a building that is partly or completely below grade plane (see “Story above grade plane” in Section 202). A basement shall be considered as a story above grade plane where the finished surface of the floor above the basement is:

1. More than 6 feet (1829 mm) above grade plane; or

2. More than 12 feet (3658 mm) above the finished ground level at any point.



GRADE PLANE. A reference plane representing the average of finished ground level adjoining the building at exterior walls. Where the finished ground level slopes away from the exterior walls, the reference plane shall be established by the lowest points within the area between the building and the lot line or, where the lot line is more than 6 feet (1829 mm) from the building, between the building and a point 6 feet (1829 mm) from the building.

HEIGHT, BUILDING. The vertical distance from grade plane to the average height of the highest roof surface.

HEIGHT, STORY. The vertical distance from top to top of two successive finished floor surfaces; and, for the topmost story, from the top of the floor finish to the top of the ceiling joists or, where there is not a ceiling, to the top of the roof rafters.

:popcorn
THE DEFINITION OF "BASEMENT" IS NOT DEPENDENT ON THE STORY ABOVE.(damn caps lock)...wether it is a story above or below grade is....
 

codeworks

Gold Member
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Jun 12, 2011
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South Texas
ok, then it's a story below grade plane. due to the reading of "height, story" and basement, and grade plane. they all apply
 

TJacobs

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It pays to read the definitions...and then read them again, and again...
 

gbhammer

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Builder Bob said:
So I can't have an unlimited area bunker style building underground ???
I don't see why you can't have an unlimited area underground building so long as it meets the requirements for a single story unlimited area building. IBC 2009 506.4 exception: single basement
 

JustReid

Bronze Member
Joined
Jul 27, 2011
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57
Location
Edwards, CA
2009 Edition on top of Table 503

"Allowable height limitations shown in feet above grade plane. Story limitations shown as stories above grade plane. Building area limitations shown in square feet, as determined by the definition of "Area, building,"per story"

So the example building from the OP is a three story building but only a one story building for purpose of height and allowable stories? (just thinking out loud). Then 506 does not mention above grade plane and the wording above table 503 does not say "per story above grade plane" it only says "per story". Sooo... is the designer to add the area for all three stories and base it on a limitation for one? I have confused myself and am sorry if I have confused anyone else :)
 

JustReid

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Jul 27, 2011
Messages
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Location
Edwards, CA
Builder Bob said:
So I can't have an unlimited area bunker style building underground ???
Section 405 kicks in at 30 feet underground and then requires Type I construction (as long as it is not one of the exceptions). If it is less than 30 feet underground then I would think it would have to be of a construction type that allows UL in 503 and then it would be allowed.
 

mtlogcabin

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Oct 17, 2009
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Big Sky Country
Look at Section 405 for underground buildings. No maximum area requirements, no maximum levels below grade. Just has to be Type I construction. I do not see any code restrictions as to the maximum size a basement (story below grade) can be.
 
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