Question about determining Required Egress Based on Section 1005 in IBC

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Aleksandar Stojkovic

September 14, 2020 03:01

Let's say that you have library that's multistory, and the top story accommodates 1200 people.

So 1200 x .2 = 240. Let's say you have four stairwells. Hence, 240 / 4 = 60.

This means that egress components (other than stairways) need to accommodate 60 inches (based on section 1005.3.2.)

Does this mean a priori that you need a double leaf door at the bottom of each stair, because a single leaf can maximum be 48 inches?

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  David Kaplan September 14, 2020 12:26 (Edited September 15, 2020 22:19)

  Yes sir, it does.  That is good that you know that as well. 

  One thing to keep in mind with stairs is that occupant load at the point of egress is not cumulative.  What that means is that, let's say you have a 4-story building, and each story is served by the 4 fire stairs that you gave as an example.  The 1st floor exit door  at each stair does NOT need to accommodate 60" + 60" + 60" + 60" = 240", and that calculation I just did is assuming that each story needs 60" of width.  The 1st floor exit door would only need to accommodate 60".  Now, if you had an upper floor that for some reason had a greater occupant load than the other stories - say that the 3rd floor needs 72" - you would need to base your 1st floor exit door on that worst case scenario.

  Hope that helps!

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  Iuliia Fomina September 15, 2020 22:13

  Very helpful!

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  Iuliia Fomina September 18, 2020 21:57

  What is the right occupant load multiplier for the egress stairs? I read 1005.3.1 dedicated to stairs, and it says to multiply the occupant load by 0.3, and in 1005.3.2 it says that all other egress components should use 0.2 per occupant.

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  David Kaplan September 18, 2020 22:09

  0.3" is the correct factor.  Stairs have a wider width requirement than other egress components.  

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  Iuliia Fomina September 18, 2020 22:31

  Thanks! Then I think Aleksandar would multiply 1200 occ. by 0.3 to get 360 inches of required staircase egress width. 360 in divided by 4 staircases would give us 90 inches width. We need each staircase to have double swing doors with 48 inches width each.

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  Gang Chen September 19, 2020 22:25

  Lulia,

  You are correct. I was thinking the same thing when I read the original post, and you beat me to it.

  Gang Chen, Author, Architect, LEED AP BD+C (GreenExamEducation.com)

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  Ashley Kopetzky September 20, 2020 22:42

  So just to make sure - you would use the .3 multiplier if you were calculating for stairs - but corridors is .2?

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  Gang Chen September 20, 2020 23:19 (Edited September 20, 2020 23:20)

  That is correct. See related IBC Section 1005.3.1, Stairway, and Section 1005.3.2, Other egress components, at this link:

  https://codes.iccsafe.org/content/IBC2015/chapter-10-means-of-egress

  Gang Chen, Author, Architect, LEED AP BD+C (GreenExamEducation.com)

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