2015 IBC 1023.2 question

[JZegowitz]

Office debate - interior exit stair extending from one level below grade to top floor of four story above grade building. The enclosure has door at basement, grade level, and top floor. What is the rating required of the stair enclosure. I say this akin to a shaft enclosure, creates floor openings, therefore 2 hour as it connects 4 or more. Someone trying to sell 1 hour saying 'connecting' is the main idea and only connects 3 floors. Not buying. What say you.

 

[walker.t]

What is the rating required of the stair enclosure.

I think 1023.2 clearly states that a 2-hour rating is required:

2018 IBC 1023.2 Construction [partial excerpt]
Interior exit stairway and ramp enclosures shall have a fire-resistance rating of not less than 2 hours when connecting four stories or more and not less than 1 hour when connecting less than four stories. The number of stories connected by the interior exit stairways or ramps shall include any basements, but not any mezzanines. [emphasis added]

Someone trying to sell 1 hour saying 'connecting' is the main idea and only connects 3 floors.

I’m not sure why they are making a point that “connecting” is the main idea - yeah, stairs connect floors, nothing special about that. But as you described the project you are connecting five stories (four above grade plus the basement,) not three.

 

[Yankee Chronicler]

I'm sure the argument is that, since there aren't doors at the 2nd and 3rd floors, the stair only "connects" the basement, the first floor, and the 4th floor.

It doesn't work that way. The equivalent would be like saying a vent shaft with an opening in the basement and a louver on the 4th floor only connects two stories.

The stair in the example connects five stories and requires a 2-hour rating.

 

[walker.t]

I'm sure the argument is that, since there aren't doors at the 2nd and 3rd floors, the stair only "connects" the basement, the first floor, and the 4th floor.

The reason the walls are rated is that fire has a way of creating a connection between a floor and the shaft even when there isn’t a door.

 

[steveray]

I'm sure the argument is that, since there aren't doors at the 2nd and 3rd floors, the stair only "connects" the basement, the first floor, and the 4th floor.

It doesn't work that way. The equivalent would be like saying a vent shaft with an opening in the basement and a louver on the 4th floor only connects two stories.

The stair in the example connects five stories and requires a 2-hour rating.

Agreed