Area/Height Increase with Sprinklers (Mixed Occupancies)



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    Tsai Tse Josh Lo

    David, Lin,

    Exception #2 under Section 506.4.1 is only applicable to Group R occupancies up to four stories. See Section 903.3.1.2 for details.

    Therefore typically, maximum allowable building area equals to maximum allowable area per story times 3.


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    Jonathan Chertok (Edited )

    here is what i am missing. there is /obviously/ nothing in the guidelines (or ANY other bread crumb trail left for professional candidates) regarding this particular issue. and we’ve collectively spent months, if not a year, dissecting the intricacies of the IBC with respect to the issue. and as much as i like chunking through the code (and i honestly do like this) - i can’t stand having to screw with this ad infinitum while studying for this exam.
    is the consensus that this specific calculation will be required in some of the exams (as the posts to the forum seem to indicate)?
    /and/ will it be “dumbed down” in some way that a monkey could answer it - without having to spend more time on it of course...?

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    David Kaplan (Edited )


    First, I want to say that I enjoy talking code issues on this forum.  I like having a dialogue with other architects on these topics, so if you disagree with my assessment below, let me know.  I’d appreciate the learning opportunity.

    This being said, I'm not sure where you are getting this, that simply is not correct.  Nowhere in 506.4.1 does it reference R Use Group in any shape or capacity.  I am sitting here with the 2012 IBC book in front of me, open to that section of the code.  This code applies to "single occupancy buildings with more than one story."  Period.

    The other MAJOR thing you have to be careful of is this: you have cited Section 903.3.1.2.  This is for an NFPA 13R sprinkler system.  This is a residential-style sprinkler system that would be used in residential occupancies.  You are correct that if you are going to install an NFPA 13R system in a residential building, the building may not exceed four stories.  This is consistent with IBC 504.2 under the "automatic sprinkler increase" section.  I would note further that if you were in fact wanting to build a residential building in excess of four stories, you would have to install an NFPA 13 system, not 13R.  We do numerous hotels around the country, all in excess of four stories this way.

    The sample question that we've all been discussing at hand is a IIB Construction Type B use building.  You would not be installing an NFPA 13R sprinkler system in a Business Use.  You would put in an NFPA 13 system, which is a commercial sprinkler system.  As such, the four story rule does not apply, but I would offer as well that it is irrelevant to this question.

    Jon – I wanted to address your point.  I agree with you to a certain extent.  I don’t think you’ll get this type of question on the exam, and more than likely you would be asked something a bit simpler, such as calculate the total allowable area per floor of a building.  That’s just my personal take but others may have different experiences to share. 


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    Tsai Tse Josh Lo


    Exception #2 under Section 506.4.1 references Group R equipped with NFPA 13R sprinkler system, by citing Section 903.3.1.2. (see photo of the paragraph below).

    Therefore, the largest possible maximum allowable area of a building equals:

    maximum allowable area per story times 4, for Group R equipped with NFPA 13R sprinkler system.

    maximum allowable area per story times 3, for all other instances incl. Group B.



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    Ariana Parrish (Edited )


    Per the (3/15/2018) comment why is the one-story building increase by 300%, I_s=3 actually I_s=2? Looking at the IBC 2015 table 504.4, occupancy A-1, (S) Sprinklered, type iib construction, i'm seeing 3. I know I'm missing something. Thanks for the help. Also in the example is the right side of this slide correct, does I_s=2 for buildings over 2 stories? 


    Also, when calculating the Tabular Area of the building, why didn't we use 34,000SF (S1, per ibc 2015 table 506.2) Since we were given that the building was sprinklered? (see screenshot below)


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