Does efficiency matter when calculating max occupants per GSF? Help with Practice Exam question
Hi! This is my first time posting! I have the PA exam early next week, and I have become very confused about the IBC’s maximum floor area calculations after reviewing a Black spectacles practice exam question. I’m hoping someone may be able to provide insight.
The question is part of a case study, so I’ll summarize:
The building in question is 4,200 GSF. An architect is approached to design a dance studio with ancillary spaces on the 1st floor, and may potentially add an additional level to the building for an exercise room. The architect advises that the additional level would have 85% efficiency.
Question: How many occupants can the client expect to have on the proposed additional level? Assume that the proposed additional level will be built with the same footprint as the building below.
Per Black Spectacles, the answer is 72 occupants.
(4,200 sf x 0.85)/ 50* = 71.4 (rounded up to 72)
*50 is the occupant load factor from IBC Table 1004.5 (the Maximum Floor Area Allowances per occupant). However, the table states the occupant load factor is “50 gross”. Since the occupancy factor is based on the GROSS square footage, would the efficiency matter? Wouldn’t the answer actually be 84 occupants?
4,200 gsf / 50 gsf per occupant = 84 occupants
I’ve been digging through the code trying to make sense of this, and have gotten more confused, so I would love clarity on this. Thanks so much to anyone who can help me out!

Hi Erica,
I think this question is confusing. The building efficiency square footage is different from what the code states as gross and net. Basically the efficiency subtracts certain areas within the space, that is why the space is 85% efficient. The gross area according to code does not subtract much area at all. If you use the table 1004.5 to determine occupancy you have to go with what the code interpretation of gross. Check out this video, it explains it more:https://youtu.be/s2tGFQhP1HY
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