Is an "enclosed" exit access stair a shaft?

[nealderidder]

Exit Access Stairs - one of my favorite topics, I still have BO's look at me like I have two heads when I say these words. Which I understand, it is confusing. Especially the way section 1019 is written.

Consider an office building in CA with two underground parking levels and two above grade floors of office use. From any point in the building I can make it to a main level exit within the allowable exit access distance. See attached sketch. Therefore I don't need any Interior Exit Stairs (CBC 1023). The two stairs provided can both be Exit Access Stairs (CBC 1019).

CBC 1019.3 tells me that if I don't comply with one of nine conditions, my Exit Access Stairs must be enclosed in a shaft per 713. So then I would have an Enclosed Exit Access Stair.

Eight of the Nine conditions are not applicable (I'm assuming N/A is different than not complying). The only condition that might apply is #4 which seems to tell me that if my building is sprinkled and I install draft curtains and closely spaced sprinklers I can have Open Exit Access Stairs in my 4 story (2 above grade, 2 below) building.

I can't have a four-story open stair for a few reasons. I've got an occupancy separation between S-2 and B of one hour, I also don't want the environments of parking garage and offices inter-connected, and there are security issues. So I will be enclosing my Exit Access Stairs.

That's the set-up, I'm getting to the questions...

1. Do I truly have two Enclosed Exit Access Stairs that must meet shaft requirements per 713? And not Interior Exit Stairs?

If you said yes to #1 - Section 713.6 tells me that if any of my shaft walls are exterior walls they must comply with section 705 for exterior walls and that the fire-resistance rated enclosure requirements shall not apply.

Section 705 tells me to look at 602 for the required rating of such an exterior wall. This building is type II-B and I've got more than 30' of fire separation distance so required rating per 602 for exterior walls = 0 hours.

2. Take a look at the sketch. In the upper left-hand corner you see a wall with double lines. That's an exterior wall that I want to make storefront for the length of the stair. Following my reasoning above, that wall is not required to be rated and this is not an Interior Exit stair. What's stopping me from installing non-rated storefront there?

3. Does your answer to #2 change if I tell you that the space to the left of the double lines on Level 2 is a balcony?

Thanks for any thoughts on this!

 

[RLGA]

Section 1006.3.1 allows egress travel through only one story to reach an exit. Thus, your B2 level requires passing through two levels; thus, the stairways, if separated from the stairways connecting stories L1 and L2, are required to be exit stairways. If the stairs for stories L1 and L2 are in the same enclosure as the stairs for B1 and B2, then the entire stairway must be considered an exit stair and have a 2-hour enclosure.

Exterior walls of stair enclosures (exit access or exit stairs) are only required to be rated per requirements for fire separation distance. If the fire separation distance is 10 feet or greater (for Type IIB construction), then no rating is required. The balcony adjacent to the stairway wall does not matter.

 

[nealderidder]

Thanks Ron. Really rained on my parade!

 

[RLGA]

Sprinkled, maybe, not rained. You still get your nonrated exterior walls.

 

[nealderidder]

Sprinkled, maybe, not rained. You still get your nonrated exterior walls.

I read that code section again (1006.3.1) and am wondering if it really means I must exit from either the story I'm on or an immediately adjacent story... The language is: The path of egress travel to an exit shall not pass through more than one adjacent story.

I read that as - You may pass through an adjacent story to reach the level of exit. So from my B2 level I may pass through B1 to reach the exit level at L1.

It's the through that gets me. If the intent was to force me to exit from the level I'm on or an immediately adjacent level, why not just say that?

 

[RLGA]

You have to look at the common definition of "adjacent," which means "next to or adjoining." Story L1 is not next to or adjoining Story B2. Since an exit access stairway is not required to discharge directly to the exterior, when leaving the exit access stair you "pass through" that story to reach an exit. In your situation, an occupant would need to pass through B1 and then through L1 to get to an exit; thus, two levels.

The "adjacent story" concept was added to the 2012 IBC (Section 1021.3.1) when the ICC's Code Technology Committee (CTC) submitted sweeping changes to Chapter 10, which affected many other chapters. Because of the extensive number of changes, the reason statement did not elaborate much on each of the changes and merely stated, "Proposed section 1021.3.1 has a provision that limits the access of exits on another floor to an adjacent level." The requirement moved around in the 2015 IBC to become a part of Section 1006.3 without a change in wording. For the 2018 IBC, it then became a section of its own (Section 1006.3.1) and the reason stated was a little more clear about the application:

The intent of this proposal is to coordinate Section 1006.3 and the allowance for exit access stairways in Section 1019.3. The 2nd sentence of Section 1006.3 currently says that the required number of exits must be available not more than one story above or below the level you are on. The first part of this proposal is to put that requirement in its own section, Section 1006.3.1. (Emphasis added; the red text originally said "exit," but that was not the intent.)​

Yes, the wording is a bit ambiguous, and you may find a B.O. that would support your interpretation of "pass through," but I have not found one yet. I got tripped up on that requirement by the fire marshal on a project I was trying to use an atrium stair as an exit access stairway (before it was allowed to be considered an exit stair in the 2018 IBC).

 

[nealderidder]

That's very illuminating, thank you. I figured the new language about exit access stairs in the 2019 code (2018 IBC) was a hint that this section was meant to reign in exit access stairs and allow 3+ stories in only very limited circumstances.

If they had actually used the line: the required number of exits must be available not more than one story above or below the level you are on it would have been much clearer.

Thanks again Ron, we'll see what this particular B.O. thinks of "through"!