I have a question about allowable area determination (506.2) in IBC.
If the building is 3 stories, Equation 5-1 should be used. In this equation, At refers to the Tabular Allowable Area Factor (NS, S1, S13R, or S13D). Although the 3 story-building may fall under SM—which is defined as “a building two or more stories above the grade plane”—SM is not listed as an option for At in Equation 5-1.
In this case, which one should be used for At—NS, S1, S13R, or S13D—when the building is 3 stories equipped with sprinklered?
Thank you so much.
@giyoungoh this is a great question! I’m tagging our PDD coaches/experts for further insight…
@coachmarissayee @coachmikeparaszczak Could either of you chime in here of what you would do in this scenario? Thank you!
Kiara Galicinao, AIA, NCARB
Black Spectacles
Hi there.
Per 506.2.1, equation 5-1 determines the allowable area of each story in a single occupancy building. Assuming the building has 3 stories, is sprinklered, and does not qualify for a frontage increase, you would multiply the S1 value by 3 to determine the allowable area of the building.
Hope this helps!
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Thanks, but would you clarify more specifically please?
Even for a building that is 2 or 3 stories above grade (and therefore falls under Equation 5-1), the SM value from Table 506.2 would not be used? In such cases, would the S1 value should be used instead—even though Table 506.2 defines the values as:
- S1 – Buildings with a maximum of one story above grade plane, equipped with a sprinkler system
- SM – Buildings with two or more stories above grade plane, equipped with a sprinkler system
I’m trying to understand if S1 have to be used (instead of SM) for 2 or 3 stories, which would seem to contradict the definitions of S1 and SM under table 506.2.
The use cases for SM under table 506.2 and section 506.2.1 are slightly different. I’d recommend reading the entire section to understand the nuances.
To summarize, in table 506.2 the term SM applies to sprinklered buildings with multiple stories.
IBC 506.2.1 has two equations, 5-1 and 5-2. SM can only be used in equation 5-2, which is for buildings of more than three stories above grade plane. For buildings that are 1 to 3 stories above grade plane, equation 5-1 (and the S1 value as stated previously) should be used.
IBC 506.2.2 has equation 5-3, under which the appropriate allowable area factor (including SM) can be used to calculate each story of a mixed occupancy building. This aligns with the definition of SM under table 506.2 where the value can be used for sprinklered buildings with multiple stories.
Thank you for the clarification. I understand that Equation 5-1 applies to single story and therefore is applicable to S1.