When is a rated corridor required

[Patrick Parsley]

I have a question on the 2006 IBC regarding corridors in a non sprinkler building with assembly occupancies. Assume the building is 6,000 square feet and the total occupant load is less than 300. It includes non-separated uses of office space and assembly space. Each assembly room has an exit directly to the exterior where one is required and two where two are required. The corridor serves as the required exit for the office space occupant load of 10. All the occupancy spaces are joined by the corridor.



Is the corridor required to be rated?



Note the exception for assembly occupancies in an E occupancy.

[Paul H.]

64 veiws,..... no comments?? I'll bite!

If the space is a "corridor" as defined by the definition of MSBC 1305.1002 - and is part of the "means of egress" as defined in 2006 IBC 1002 - a corridor is always required to be rated,..... unless exempted by table 1017.1 (A conservative approach.)

Your trick question/design has to do with the "required" occupant load into the corridor. None of your spaces are "required" to exit into the corridor. You say all rooms/spaces meet their exit requirements by exiting direclty out, but they also have an extra exit door into the corridor. That said, I think you have to assume some kind of extra load from those spaces going back into the corridor - even with exterior doors providing exiting direclty out. By adding some of that load into the corridor, it would place your load over 30 and require a rated corridor per Table 1017.1.

I think you have to keep in mind that the people using the building - and all the spaces off the corridor - probably use the building main entrance and the corridor to get to those adjacent spaces on a regular basis. Even though each space "exits" direclty out with all its required exits, the corridor has an ability to receive a large load if most of the persons go back the way they came in. AND, even if your building is only 2/3 "A," you will still have an assembly load of about 265 persons in adjacent spaces. Unless a teacher or daycare professional is in the room to tell everyone to exit direclty outside in an emergency (as allowed per exception 1 of 1017.1), Group A and B people are not smart enough to exit direclty out. Some will obviously go back into the corrridor and get you a combined load of more than 30 persons (thus, a rated corridor).

In conclusion, I think I can also make a good argument for a non-rated corridor in this design too, but I'm not going to go there on this board. I'll wait to see if someone else does that for me.

Paul H.