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2012 IBC, Sec. 506.3 200% versus 300% (a weighted average if you have a small area 2nd level)
October 16, 2017
3:24 pm
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Forum Posts: 1
Member Since:
May 26, 2016
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Given:  An existing Type V-A (fully sprinklered NFPA 13 system) building of 55,000 s.f. on the main (ground) floor, with 6,500 s.f. on a second floor.  E occupancy building constructed under the 1988 UBC.  Because of several limitations related to the site and other existing school buildings, a proposed expansion of the main level with an additional 1000 s.f. would bring the total to 56,000 on that level, 500 s.f. over the Aa total allowable for one level of 55,500 s.f.  Is there any code adoption history that would allow the 200% (allowed increase for more than 2 story buildings) to 300% (allowed increase for buildings of 1 story) of Sec. 506.3 to be a sort of "weighted average" based on the small 2nd floor of this building?  What were there, if any, as to reasons for allowing 300% (one story building) versus only 200% for buildings more than one story, during the adoption process for this section, debates, records of fires, etc.?  Would a relatively small 2nd story (11% of the lower level) increase the risk compared to a similar building of the same (or higher) overall height that is only one-story?  In this particular case, the 2nd floor does NOT qualify as a mezzanine.  Also, because of grade level changes, this area of concern (6,500 s.f.) is considered by definition a 2nd level (and, would to God, we could just change the grade around the building).

Is a single-level building (even if much higher) inherently less dangerous than a 2-story building, and if so, does the "weighted average" of how much 2nd level is smaller (in foot print area) than the main level make sense for allowing increase in the main level area?