Allowable building area per IBC table 506.2


During last Sunday’s (November 16th) PA workshop with coach Elise Renwick we worked on an exercise using the Zoning and IBC codes. One of the questions looked like this:

  1. Assuming the building is Mixed use, non-separated, construction type II-B and fully sprinklered, what is the allowable area of the building?

The answer was – 28,500 sq ft per IBC table 506.2 (using A-3 occupancy as the most restrictive among the given).

My question is – by “allowable area of the building” do we mean the building footprint area or the total area of all floors?

If it is former, then the above answer seems to be correct as per 506.2.3, which says “No individual story shall exceed the allowable area (Aa) as determined by Equation 5-2…” (However, that refers to single-occupancy, multistory buildings. I could not find a similar clause for the mixed-occupancy, multistory buildings).

But if we actually mean the total area of all floors, then our answer should be at least the triple of 28,500 i.e. about 85,500 sq ft as per 506.2.4, which says “Each story of a mixed-occupancy building with more than one story above grade plane shall individually comply with the applicable requirements of Section 508.1. For buildings with more than three stories above the grade plane, the total building area shall be such that the aggregate sum of the ratios of all the actual area of each story divided by allowable area of such stories, …, shall not exceed three.”

If we calculate the Frontage it will add even more square footage to our allowable area.

I know all above sound pretty convoluted, but then again, what is the right answer – 28,500 or 85,500?


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@coacheliserenwick do you mind helping Andrew?

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