Mixed use

[DwightB]

2007 IBC, mixed use of an open room, re: 1004.9, "where two or more occupancies - use the most stringent". Suppose I have a large open room, such as a common space in a student union on a campus. I have a traffic way on the plan that provides for exiting that divides the space. 20% of the space on one side of the walkway is "assembly-concentrated" and planned to be a seating area. 80% (ignores space occupied by the walkway) of the space is "assembly-unconcentrated" and will be used for dining.

If I compute the 20% at 7sf/person and the 80% at 15sf/person as it will actually be used, I will have an exit capacity much more realistic, but much lower than if I must compute the entire room at 7sf/person, which is not the intent of the owner.

What is the proper term for the traffic way? It can't be a corridor; there is no fire rating. It's more like a fire lane in a parking lot, but I don't see anything corresponding in the building code that allows me to design an exit path and then compute occupancies for remaining areas upon realistic factors. WalMart does it with red tape. We could have a change in flooring or an arrangement of planters to designate the walkway.

What's the legal way to handle this? It goes back to 7sf/person for all areas again, I think. Right?

 

[Frank]

The traffic way is an aisle. The aisle may often be designated with different color or texture of floor covering, but this is not a code requirement in most areas.

see 2009 IFC sect 1028 esp 1028.9

See 1004 for calculating occupant load, individual areas can be considered and calculated separately based on the intended use and then the max occ load posted.

See how airport concourse and waiting areas have different occupancy factors but are usually not physically separated

 

[mtlogcabin]

I would use the 7 sf/person for the entire area for egress width and number of exits. Then use the 20%/80% for the OL of the space and post it that way.

A student union can have a significant load during certain events over and above the "normal" uses.

 

[FM William Burns]

Since it is an assembly occupancy/use wouldn't the aisle be considered "standing" area technically speaking which allows for a more conservative figure of 1/5 to be applied for floor area? I do not have issues with MT's rationale either and would approach it this way also

 

[DwightB]

FM Burns: I'd say no to your comment because a hallway or corridor has no occupant load, neither does an aisle. If an aisle contributed to occupant load, I'd be totally screwed on every assmebly design where I have the max of 14 seats between aisles. If an aisle was allowed as standing space, I'd have additional occupancy in that row that I would have to accommodate and yet would have no exit capacity if the aisle was filled at the standing person factor. That's why I often see "the fire marshal does not allow standing/sitting in the aisle".

 

[JustReid]

FM Burns: I'd say no to your comment because a hallway or corridor has no occupant load, neither does an aisle. If an aisle contributed to occupant load, I'd be totally screwed on every assmebly design where I have the max of 14 seats between aisles. If an aisle was allowed as standing space, I'd have additional occupancy in that row that I would have to accommodate and yet would have no exit capacity if the aisle was filled at the standing person factor. That's why I often see "the fire marshal does not allow standing/sitting in the aisle".

An aisle in a fixed seating area is different. There will not be somebody there to usher students out of the "aisle" in the student union. Will loading the "pathway" put you over on available egress width? If not load it like MT said to cover your assets. If so, put another door...to cover your assets. The posted occupant load could get enforced by the campus fire marshal so make sure the client is not fudging the actual use of the space. I remember my student union being packed at times (beginning of semesters, special events, etc.).

 

[FM William Burns]

Thanks DwightB and totally understood. I was just working on a space that meets similar concerns that JustRied mentioned. The seating area is off to one side of a food court and there is considerable open floor area that is exit access and not "waiting" where congregation can and will occur. This area is not separated by barrier, wall or designation as a corridor or exit access aisle can be considered but must be considered as something since it adds to the occupant load and egress capacity figures does it not? The only reasonable option is "standing" for an assembly occupancy >50 and when one is trying to avoid exceeding the 100 person occupant load figure.

 

[permitguy]

Assembly areas without fixed seats are calculated based on net floor area per the table.

FLOOR AREA, NET. The actual occupied area not including unoccupied accessory areas such as corridors, stairways, toilet rooms, mechanical rooms and closets.

I don't know that I'd allow a DP designated "traffic way" to be removed from the calculation based on the definition, no matter how it's designated.

Out of curiousity, is this at Missouri Southern?

 

[gbhammer]

I have to agree with FM. I have had designers for banks that try and say that the lobby should not be counted in the design occupant loads, and when I ask them if they have ever stood in line at a bank at 5 a clock at the end of the month; they say well that only happens once a month.

 

[DwightB]

permitguy: Actually my question refers to a large church in Florida that I've designed, but this one area is more similar to a student union, with areas for Wii Games, ping pong, billiards, dining, and reading. Exit capacity isn't really an issue, I have plenty of exits and stair capacity. I just thought there should be some way to divide the various functions with a legal term (I like aisles, but always used them adjacent to assembly seating, not really between dining and reading areas). Also, it didn't seem justifiable to throw everything into the 7 sf factor, since much of the area really is dining, and ping pong, pool, and foosball all require tables.

 

[permitguy]

Cool. I have several big churches in my jurisdiction with similar rooms for youth groups. As indicated above, there's no problem with using different OL factors for different areas of the same room based on use. Code doesn't require any differentiation between them as long as exit access is maintained. I usually see it a dashed line on the egress plan. It seems wise to design egress for the worst case, even though it isn't required. I've run into a few of these where things had changed significantly over the years with no plan review.

 

[TJacobs]

I'll bet if they have a speaker or a celebrity visitor your "no standing in the aisle" just flew out the window.

If you go to the United Center (Chicago) in the main entry they have multiple occupant load placards for a Bulls game, Blackhawks game, concerts, etc. Maybe 6 or 7 different arrangements. I know this is not a major stadium but the concept is the same.

If you create egress plans for each possible type of occupant load, you have covered the bases. I know I would feel better as the AHJ.

 

[gbhammer]

I've run into a few of these where things had changed significantly over the years with no plan review.

Yep, that can be an issue if over time they go beyond the intended use of the space. If it is sprinkled and you have worse case scenario exits, the only other thing I would look at is plumbing fixtures. Schools and churches have a tendency to want to ignore the design occupant load for fixture requirements (IBC chapter 29 gets them riled every time).

 

[Paul Sweet]

I'd base exits on one person per 7 SF, but cut them some slack on the nunber of occupants to calculate plumbing fixtures.