Basement vs first floor above grade

[Big Mac]

One of the provisions for determining whether a floor level is a basement vs a floor level above grade is the actual average grade around the lowest floor level, and the difference between the floor level above and the average grade plane. Typically the lowest floor level is an area equal to the footprint of the floor above, so the average grade plane would be established based on the entire footprint of the building. That is what is illustrated in Figure 502.1(2) in the Commentary.

However, in some cases, the lowest floor level is only a portion of the area of the floor directly above. For example the lowest floor level might be 7,000 square feet and the floor level above might be 12,000 square feet. Under the second condition would you use the entire footprint of the building to determine average grade or would you use the perimeter of the walls surrounding the lowest floor to determine average grade plane?

This becomes an issue as to whether V-A or V-B construction could be permitted for Type of Construction on a 'Use Group R-2' occupancy structure, for example. If it is three-story with a basement, perhaps V-B construction would be adequate. But if it is a four-story structure, V-A type of construction would be required. Obviously in either case a sprinkler system is required.

Looking for feedback.

 

[brudgers]

How well does the proposed solution address the hazards for which the relevant code sections are written?

 

[steveray]

I would have to read it....but I seem to remember that it is all based off of the first floor that is above grade at any point.....find grade plane, if it exceeds 12'(?) at any point...it's a story above grade...then it goes to averages and so on....you have the max height and average height to look for....don't have time right now to look deeper in to it, but I believe you would use the area of the "upper floor....

 

[mtlogcabin]

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.

Wherever grade adjoins an exterior wall. This could include 2 or more levels on a sloped property.

 

[steveray]

I think MT got it.......And don't forget the other definition.....

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;

2. More than 6 feet (1829 mm) above the finished ground level for more than 50 percent of the total building perimeter; or

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

 

[annoyitated]

Where does No. 2 exist in the 2009 or 2012 codes? Or is it a logical interpretation?

 

[cda]

Where does No. 2 exist in the 2009 or 2012 codes? Or is it a logical interpretation?

See basement, see if that helps

http://publicecodes.cyberregs.com/icod/ibc/2009f2cc/icod_ibc_2009f2cc_5_par003.htm?bu2=undefined