unenclosed stairs

[Plans Approver]

A fully sprinklered, 2 stories plus basement, B use group, complies with all code sections except (maybe): 06 IBC 1024.1, Exceptions 1 & 2.

1024.1 Exits shall discharge directly to the exterior of the building. The exit discharge shall be at grade or shall provide direct access to grade.

Exception 1 allows a maximum of 50% of the exits to discharge through areas on the level of exit discharge when meeting the 3 sub-exceptions (basically a lobby). In this case, the exit stairs are unenclosed per 1020.1, Exception 9 from 2nd to 1st floors, basement stair enclosed w/ discharge at grade.

How do unenclosed stairs meet the requirements of 1024.1 or Exception 1 without some type of enclosure for the 2nd stair w/o making it an exterior stair or using a vestibule?

Would you permit both a lobby and a vestibule? 50% of exits to each? (I think I would.)

 

[Coug Dad]

The exit from the second floor is the door to the outside. Normally in a multi story building, the exit on the upper floors is the entry to the stair enclosure. With an allowed open stair, the exit travel distance includes the distance down the stair and to the door to the outside. Therefore, under this two story scenario, all exits lead to the outside.

 

[Plans Approver]

Thanx, Coug.

I guess unenclosed stairs are inherently safer than enclosed stairs in the same situation. An enclosed stair would require the area where the enclosure discharges onto the grade floor to have the basement floor-ceiling 1 hour fire rated and only one (50%) stair could do that. We haven't adopted 2009 IBC yet, but, 09 seems to have cleaned this situation up a bit in limiting the connecting floor to a max. occ. load of 10.

 

[peach]

I will be meeting on just this issue next week. 26' x 100' x 10 story building... new enclosed stair (to replace a nasty dangerous fire escape) in the back.. current uneclosed stair stops at the 4th floor opening to an atrium... curious what everyone else might think.

 

[RJJ]

peach: If I understand the issue the new enclosed stair is only going 4 stories of the 10? How does the exit enclosure work going above that point? Are there exit enclosures into the atrium and thus discharge to the outside stair tower? Not sure of all the issues!