Exterior stair and rating of not-directly-adjacent wall

[jteselle]

My building is an addition to an existing building of Type III-B with NFPA 13 sprinklers, and R-2 occupancy, three stories. There is an existing exterior steel stair that serves as egress from the 3rd and 2nd floors. The addition requires that we relocate the portion of the stair leading from the 2nd floor down to grade. Attached is a portion of the floor plan showing the situation.

I have studied IBC 2018 paragraph 1027.5 and 1027.6 about exterior stairs and ratings of the exterior wall. My understanding is that paragraph 1027.6 applies to the portion of the exterior wall that is immediately adjacent to the stair -- that is the part shown with a red dotted line in my plan. There are no specific dimensions given about how much of the wall must be protected but that seems to be how this is interpreted.

In some online postings and diagrams that I have found, there is reference to a need to fire rate any portion of the exterior wall that is within 10 feet of the stair. But I don't specifically see that in the 2018 IBC. The only reference I see is in paragraph 1027.5 where it refers to "a minimum fire separation distance of 10 feet .... to other portions of the building." Is that where people are getting this 10 foot rule?

If so, there is a following part of this paragraph that reads "other buildings on the same lot unless the adjacent building exterior walls and openings are protected in accordance with Section 705 based on fire separation distance." Is that where this 1-hour rule of 10 feet comes from? Also following that text in the IBC is this: "For the purposed of this section, other portions of the building shall be treated as separate buildings." Somewhat confusing.

Anyway, what I wonder is this -- it appears that only the immediately adjacent portions of the wall (per 1027.6) need to be 1-hour rated explicitly (1027.6 refers us to the separation requirements of 1023.2 which implies a 1-hour rating for a 3-story building). The portions of the wall within 10 feet, if we are getting that from 1027.5, don't have to be treated in the same way. They have to comply with Section 705.

When I go to table 705.8 (and Table 602), for the portion of the wall more than 3 feet but less than 5 feet from the stair must be 1-hour rated and may have up to 15% unprotected openings -- the openings appear to be the big difference from the wall immediately adjacent to the stair. Here openings are allowed, and they can be unprotected up to the 15% limit. From 5 to 10 feet we can have 25% unprotected openings.

Do you think my interpretation of this is correct? It matters because I can't easily rate the windows and would like to keep them.

Related to this is how we measure the distance from the stair to the wall. On the plan it is measured in plan view. But if you view the stair in elevation, do we draw a 10-foot radius circle from the edge of the landing or the top of the guardrail and say that is the part of the exterior wall within 10 feet of the stair? Reading it literally that seems right to me. One could perhaps argue that the height of a person on the stair would be relevant somehow but that is not called out anywhere.

Sorry for the long post -- thanks for any thoughts on all this!

 

[Joe.B]

You say "relocate a portion of the stair", are you rebuilding it, replicating it, or starting from scratch? I ask because of 705.2.3.1 which would determine if you had to extend the sprinkler system to protect the stairway. That might affect your answer to the other question.

Check out exception 3 to 1027.6

 

[jteselle]

Thank you for those comments. This is a steel stair and we are removing the lower portion (everything below the flight indicated as "Up" on my drawing) and then adding on the switchback part shown as "Down". It seems to me that 705.2.3.1 applies to stairs of combustible construction so that would not be relevant here.

Also exception 3 to 1027.6 (and exception 2 as well) seem to me to apply to a situation like a second-floor motel corridor that is open to the air and has at least two exterior stairs connected to it. My project does not have that condition. Do you see something differently?

 

[Joe.B]

I really don't know enough about your situation to give you a better answer. What's your role in the project? What is the addition and how does it affect the walls in question? What's the bigger picture, and what's the bottom line? What I mean is a short summary of the project and what your end goal is. For example, if you're the property owner are you hiring help to design plans or doing it yourself? If you're the designer is there an Architect involved? Have you talked to your local building department yet? Have you talked to an engineer about calculations for the stairs?

BTW I don't know that I would automatically consider a "steel stair" to be non-combustible, I would need to see more information on it.

 

[jteselle]

To answer your questions -- I am an architect, hired by the owner of the building. As shown in the plan, the stair is directly adjacent to existing exterior walls but has new exterior walls near it. The bottom line is that I want to determine how much of the new walls must be rated, in what way, and if any unprotected openings are allowed (as noted in my original post).

I have met preliminarily with the local codes officials and am planning a second meeting. Really my reason for posting here was to see if others have interpreted the code as I am doing, or if I'm missing something in my understanding of where the "10 foot rule" comes from.

As for the non-combustible steel stair, I am confident that our local code officials would consider it so. In any case, I don't think that section 705.2.3.1 is relevant to what I am trying to figure out.

 

[Paul Sweet]

If it was a new stair the rated wall (and window) would have to extend 10 ft. to the left of the landing. Since it's an existing stair you should be OK if they are using the existing building code.

 

[jteselle]

Thank you -- that is useful. I am interested still in knowing where the 10 foot rule comes from. Is that from the oddly-worded 1027.5 paragraph?

 

[aldidog]

You may be thinking of an exterior area for assisted rescue (1007.7 in 2012 IBC). That has specific language about the how far the separation shall extend. Exterior exit stairways (that serve more levels than the the level of discharge) and exterior area for assisted rescue that serve a landing for stairs at the level of discharge routinely get flip-flopped.

 

[jteselle]

That is a part of the code I had not been aware of before. Probably there are many such. In the 2018 IBC it is 1009.7 and there it does explicitly call out the 10 foot boundary for the exterior wall rating. Also it says under the exception that this is not required in a fully-sprinklered building (as ours is).

 

[Paul Sweet]

2018 IBC 1027.6 says "Where a vertical plane projecting from the edge of an exterior exit stairway or ramp and landings is exposed by other parts of the building at an angle of less than 180 degrees (3.14 rad), the exterior wall shall be rated in accordance with Section 1023.7."

The wall to the left of the stair is only at a 90 degree angle.

 

[jteselle]

Right -- so this is what's not clear to me: if that wall adjacent to the stair must be rated, how far out does the rating extend? If the wall is 100' long and the stair only sits on 20' of it, is the entire wall rated? Seems that some people come up with a "rule" that 10' to either side of the ends of the stair need rating. As noted in my original post, I don't see where that is called out in the code.

Or perhaps the wall only needs to be rated where it is directly adjacent to the stair -- not off to the sides at all. It is hard to find a clear answer in the code.

 

[Jay Smith]

When 1027.6 sends you back to 1023.7 you find the 10 feet.

 

[jteselle]

Thank you! Now I see it, and of course it should have been obvious. This makes it much clearer.