Story above grade plane 12' rule

[georgia plans exam]

Does anyone know the reasoning behind the 12' rule in the definition of "story above grade plane"? I understand the code requirement, but I just don't understand why that if a story is more than 50% underground, but a small portion of that story has the finished surface of the floor above exceeding 12', it cannot be considered to be a basement. GPE

 

[Frank]

It is considered both a basement and a story above grade. The story above grade rules for basements came about as some developers, particularly of apartments were using 1 inch basements to get another story in type 5 construction. Like most numbers in the code the 12 ft was agreed on as somewhere you need to say this is waddling and quacking so it is a duck.

 

[khsmith55]

There has always been a fatal flaw with the 12' requirement in the definition when it comes to underground parking garages. Technically speaking, if the bottom of the ramp is more then 12' below the floor under consideration then the underground garage is the first story. Thank goodness most jurisdictions are not enforcing this glitch.

 

[Paul Sweet]

This is arbitrary and can lead to problems in buildings on hillsides. We have a college classroom building where grade is a few inches below the main floor for 75% of the perimeter, but there is a basement less than 10% of the building area with a mechanical room and grade-level enterance. The 12' at any point rule turns what is logically a 2 story building with a basement into a 3-story building.

 

[khsmith55]

Is it just me but it seems the I-Codes are having difficulty getting on their legs. On this topic, I believe they have changed this definition in every code cycle since the I-Code inception (2000, 2003, 2006, 2009 and 2012). It also seems every code cycle is more of a “clean up” of stupid stuff they put in the previous cycle, or more restrictions my nanny needs to protect me from taking personal responsibility and exercising good judgement. Not to date myself, but the ole 1976 UBC seemed short sweet and to the point when it came to life safety issues of exiting, construction types, fire resistive construction and not to be worried about tamper proof caps on freon lines to keep kids from hyping freon. For the most part, each new cycle of the UBC addressed new technologies and substantial /realistic building research, not cleaning up previous poor judgements or political correctness.

 

[georgia plans exam]

If I remember correctly, the UBC defined a basement as a story greater than 50% underground. Made sense. I have a large project that may have to go to a higher type of construction because of the 12' rule. I just can't wrap my head around the intent of the 12' rule. There must be a reason it was put into the ICC. It has been there since 2000... GPE