Stair separation & continuity of fire barriers around primary and secondary members

[Dinheru]

R2 use - 4 floors - 3B construction -
Currently exposed wood beams and columns, 3x14 floor joist. pretty typical warehouse
13R sprinkler, with chapter 420.2/3 and the chapter 708.3/711 requirements this is 1 hour between unit partition and floors.
(I think I can do a 30 min corridor but that's not the issue here.)

Constructing a new stair , and ideally this would be constructed somewhere between my column and beam grid as a continues shaft. but following tread and riser count I need to extend my stair a few grids.
Stair connects 4 floors and requires 2 hour per 1023.2
707.5 Stair is constructed as fire barrier, and needs to extend to deck, not to rated assembly

I'm having primary structural members, column and beams inside my stairway that outside my stair connects several bays into the building.
My stair shape is odd as we are following building outline and existing openings adjacent which means I have framing that I need to cover aswell.
Exposed structural members triggers the 704.1, 704.2, 704.3 and 704.4 requiring me to fire rate columns, beams, joists and their connections even.

These sections aren't really clear on how far to extend this 2 hours through the building. I can wrap everything in the stair that is exposed with a 2 hour drywall and box it out. I believe the essentials is that is protected from both sides.
Since my framing is intertwined do I need to extend this fire rating from my initial barrier, to the floor assembly package, upgrading everything to a 2 hour separation?

It is hard to verbalize. See image attached

 

[Yankee Chronicler]

The basic rule is that any structure supporting a 2-hour assembly must be protected to 2 hours. IBC 704.1, 707.3.2, and 707.5.1

 

[Dinheru]

The basic rule is that any structure supporting a 2-hour assembly must be protected to 2 hours. IBC 704.1, 707.3.2, and 707.5.1

And that continues column after column after column ,until I hit a lets say full 4 story masonry wall correct? Not just 1 grid as that is the next bay over where the loads transfer to a different set of beam and column correct?

 

[Yankee Chronicler]

And that continues column after column after column ,until I hit a lets say full 4 story masonry wall correct? Not just 1 grid as that is the next bay over where the loads transfer to a different set of beam and column correct?

Not correct. It extends only to the beams and columns that actually support the stair enclosure.

 

[Paul Sweet]

The floors at offsets also need to be 2 hour rated, so any walls, beams, and other structural members outside the stair enclosure that support the other end of this floor framing also require a 2 hour rating. This can get incredibly complicated, especially if the building official will not permit any breaks in the fire-rated gypsum board.

 

[Yankee Chronicler]

Paul Sweet is correct. I hate fire stairs with horizontal offsets in the enclosure, because it causes problems. The horizontal portions need to be rated the same as the vertical shaft walls, and everything supporting any part of the shaft enclosure has to be rated the same as the shaft.

Here's my quick take on where your rated construction has to extend:

 

[steveray]

And that kitchen and assumed bathroom piping would likely not be allowed to penetrate the exit enclosure...1023.5

 

[Tim Mailloux]

Not correct. It extends only to the beams and columns that actually support the stair enclosure.

any beams / structure / floor assemblies supporting the stair and fire farrier needs to be rated to match the fire barrier ratting. and any columns supporting those beams / structure also need to be rated.

 

[Tim Mailloux]

deleted

 

[Yankee Chronicler]

any beams / structure / floor assemblies supporting the stair and fire farrier needs to be rated to match the fire barrier ratting. and any columns supporting those beams / structure also need to be rated.

I disagree. Anything supporting any part of the rated stair enclosure must be rated, but the stair itself does not require any rating.

 

[Tim Mailloux]

I disagree. Anything supporting any part of the rated stair enclosure must be rated, but the stair itself does not require any rating.

I agree with you, and I should have been more clear. I was speaking architect and using stair to mean stair enclosure.

 

[Yankee Chronicler]

And thhis means that the beam we see running through the stair enclosure in the sketch probably supports part of the floor supporting part of the enclosure wall, so that beam and the column supporting it will have to be rated. And since that column doesn't extend down to the foundation, the floor supporting the column will have to be rated.

I don't understand why the stair enclosure is as large as it is. It looks like a lot of wasted space. I would try to reduce its footprint as much as possible, in order to minimize horizontal offsets requiring additional rated elements.