Stepped Aisle in Assembly Seating

[MKALLAY]

I am looking at a condition in an assembly space that raises questions regarding a stepped aisle leading to an upper gallery seating area. The area has three tiers of seats, with a stepped aisle as shown:



Each of the treads on the steps is 11" wide, but note that on the second tier there is a wider segment (highlighted in yellow) corresponding to the level of the access aisleway. Is this permitted? My initial comment to the designer is no, this can't be done, because the surface does not qualify as a landing (insufficient depth in direction of travel), but then it seems it must be seen as another tread, and then 1030.14.2.1 (2021 IBC) requires treads on stepped aisles to have dimensional uniformity. Am I missing something? Is the highlighted portion considered a tread on the stairway, or can it be thought of as something else, e.g. an extension of the access aisleway?

 

[steveray]

@bill1952

 

[walker.t]

I am looking at a condition in an assembly space that raises questions regarding a stepped aisle leading to an upper gallery seating area.

This isn’t an answer to your question but it might affect your question or the answer.

Looking at the drawing I’m wondering if the line beside “DN” (on each end of the middle 3’-8” dimension) is maybe an error. Notice that the arrow with the dot (presumably set on a riser) is set on a line with a dashed line beside it (indicating a nosing projecting over the riser.) Maybe the line next to “DN” is a change of materials and not a change in elevation. Or maybe the placement of the dot on the dot/arrow line is incorrect. But if the line next to “DN” is a change in elevation, would it have to also have a nosing to match the other risers?

 

[bill1952]

@bill1952

Your reading is correct. Uniform tread depths. There is a provision (since 2012 edition) that allows for a "transition" which I don't believe will help. I think it's crystal clear, so do many of my colleagues, and ICC staff agrees.

What can I share that helps you convey this? It started with research in 1960s, Jak Paul's, and was somewhat codified in the 1985 BCMC report on MOE, after which a lot of changes in the legacy code and then the BCMC report was used as basis for 2000 IBC. If you want just a quick glimpse, 30 minutes, Google "A Stair Event". It was the beginning, and basis for handrails in aisles as well as the uniform tread depth versus the short-long or short-short-long.

 

[walker.t]

because the surface does not qualify as a landing (insufficient depth in direction of travel)

Note that under 1030.14.1 Ramped Isles, we have 1030.14.1.1 Landings, but there no mention of a requirement for landings under 1030.14.2 Stepped Aisles. Also interesting is…

2021 IBC Commentary on 1030.14.2 Stepped Aisles
What must be recognized here is that stepped aisles are part of the floor construction and are intended to provide horizontal egress. Tread and riser construction for this purpose should not be directly compared to the requirements for treads and risers in conventional stairways that serve as a means of vertical egress.

Also, if landings were required there’s not enough space at the top tier for a landing either.

but note that on the second tier there is a wider segment (highlighted in yellow) corresponding to the level of the access aisleway.

Assuming the upper riser is at the line with the “DN” next to it (3’-8” from the wall on the left,) we have 3’-8” + 1’-10” = 5’-6” for the total run of the treads, divide that by 5 equal treads to get 66”/5 = 13.2” treads.

 

[MKALLAY]

This isn’t an answer to your question but it might affect your question or the answer.

Looking at the drawing I’m wondering if the line beside “DN” (on each end of the middle 3’-8” dimension) is maybe an error. Notice that the arrow with the dot (presumably set on a riser) is set on a line with a dashed line beside it (indicating a nosing projecting over the riser.) Maybe the line next to “DN” is a change of materials and not a change in elevation. Or maybe the placement of the dot on the dot/arrow line is incorrect. But if the line next to “DN” is a change in elevation, would it have to also have a nosing to match the other risers?

Yes, the arrow to the right of the text DN is not correct - the line aligned with the edge of each tier should be a riser as well (3 risers for each tier) The wonders of BIM drafting! How I yearn for the dark ages and mylar, plastic lead, and my trusty electric eraser!

 

[MKALLAY]

Your reading is correct. Uniform tread depths. There is a provision (since 2012 edition) that allows for a "transition" which I don't believe will help. I think it's crystal clear, so do many of my colleagues, and ICC staff agrees.

What can I share that helps you convey this? It started with research in 1960s, Jak Paul's, and was somewhat codified in the 1985 BCMC report on MOE, after which a lot of changes in the legacy code and then the BCMC report was used as basis for 2000 IBC. If you want just a quick glimpse, 30 minutes, Google "A Stair Event". It was the beginning, and basis for handrails in aisles as well as the uniform tread depth versus the short-long or short-short-long.

Thanks for this - yes, I believe I have seen this video before. I'll have to look it up again.

 

[MKALLAY]

t
Note that under 1030.14.1 Ramped Isles, we have 1030.14.1.1 Landings, but there no mention of a requirement for landings under 1030.14.2 Stepped Aisles. Also interesting is…

Also, if landings were required there’s not enough space at the top tier for a landing either.


Assuming the upper riser is at the line with the “DN” next to it (3’-8” from the wall on the left,) we have 3’-8” + 1’-10” = 5’-6” for the total run of the treads, divide that by 5 equal treads to get 66”/5 = 13.2” treads.

Interesting point - so if a landing is not necessarily required at the top and bottom off separate stair runs, does one still have the option of providing them? And if so, is there no restriction on depth?

Thank you to all who responded above!

 

[walker.t]

Yes, the arrow to the right of the text DN is not correct - the line aligned with the edge of each tier should be a riser as well (3 risers for each tier)

OK, thanks for the clarification on the stair risers.

so if a landing is not necessarily required at the top and bottom off separate stair runs, does one still have the option of providing them?

I think the general concept is that if something is not specifically prohibited by the code and does not conflict with a stated requirement in the code that the designer may opt to do that thing.

And if so, is there no restriction on depth?

I don’t see why there would be a restriction on the depth of the area at the top of the stepped aisle (the “landing”). For example, if we compare this with 1011.6 (Stairway Landings,) that provision states a minimum landing depth, not a maximum depth.

 

[bill1952]

One of the reasons it was changed from "aisle stair" to "stepped aisle" was to not require landings at top and bottom.

With rows at 38" back to back I'd do 12.67" treads.

BTW something off about seats. I know you want stagger but that gap from second row at first seat will be a killer. Stagger usually achieved by seat widths so ends are aligned. Or you can add railings. In my opinion, with maye 150 theatres in my career, you need more than 5 1/2 " extra at back row for back pitch. I always show 12. 8 is probably enough but someone comes in at some point and I sisters some acoustical material needs to be added. And I don't like those oily spots on wall from hair. Also seats do not appear to be drawn with same spacing as rows. Last row looks too close to rear wall. Hopefully seating manufacturer will help you in submittals but beware.

 

[MKALLAY]

As a footnote to the above discussion - I came cross this, which I found informative:

https://www.iccsafe.org/wp-content/uploads/Pauls-Appeal-to-ICC-re-RB116-19.pdf

And quite a lot of other material is out there relating to Jake Pauls!

 

[bill1952]

Jake has never been one to rely sound bites.