NFPA 221 double fire wall

[Sifu]

I'm using this thread to again address a similar fire wall question rather than bring up a new thread and cover the same info.

R2, VB, S, 2021 IBC. Might be a stupid question that doesn't require any knowledge of the building in question. But it might help my understanding.

What is a double fire wall assembly? Not defined or described by the IBC as far as I can tell, loosely described in NFPA 221. I'll illustrate it with a specific proposed assembly, U347. Is U347 (below) a double fire wall assembly?

Or, is it two 1-hr walls? Or is it two unrated or rated supporting walls in plane on either side of a single fire wall comprised of 2 layers of shaftliner that has a 2-hr FRR by itself?

The DP illustrates the walls this way. He shows the 2-hr FW as W2-1 as only the shaftliner core, and the framed walls on either side as 1-hr walls.


706 tells us the materials, the required rating, the requirement for structural stability, and the various continuity scenarios. So it is a performance driven code section; find a wall that meets all of these requirements, and it can be a fire wall. We have discussed double fire wall assemblies, that MAY meet all the requirements but the only place the code really specifically hints at double fire wall assemblies is the allowance to use NFPA 221, but 221 is for more than just double walls. Is the IBC saying the only double wall fire wall allowed is the NFPA version?

The project I have now is similar to all the projects I have had trouble understanding in the past. A type V, with fire walls to reduce building area, with HE's, and only a single opening protective in the fire wall with dual egress doors. It would seem like I should have all this down by now, but every time I get hung up here. If the actual fire wall is only the core, thereby making a single fire wall, then maybe they can detail an independent support for the opening to remain in place, but if it is a "double wall" fire wall, the IBC will require an opening in each wall. They don't propose an NFPA 221 wall, so I am just leaving it out of the conversation for now, but since the IBC only seems to allude to double walls in the context of 221 I am not sure I can do that. Or is the use of this assembly required to follow NFPA 221 as a double fire wall?

 

[steveray]

That is not a double wall IMO....The 221 double wall concept just lets you make each "exterior wall" bearing and a lesser rating than a single wall....I believe the U347 is a facing wall and that facing wall is needed for the temp rise on the other side, IE, it is part of the rating....

 

[Sifu]

That is not a double wall IMO....The 221 double wall concept just lets you make each "exterior wall" bearing and a lesser rating than a single wall....I believe the U347 is a facing wall and that facing wall is needed for the temp rise on the other side, IE, it is part of the rating....

I have not heard the term "facing" walls, but that is the gist of the questions I have. If it is not a double wall then a single opening is permitted but only if the opening protective remains in place upon loss of one of the facing walls, assuming the actual fire resistive layer (2-1" gyp panels) remains in place. So if this is the case I have a couple questions:

1) The only place I have seen details for hanging (for lack of a better term) the door and frame from the gyp, and supporting the door and frame on the gyp below is via an ASW, which technically doesn't allow openings (and isn't specifically covered by the code), so do the H-studs and gyp carry the load from top to bottom independent of any support from the facing walls? I have seen a "portal" concept, approved by AMMR twice before, and written about by RLGA, but outside of that is there some method by which this is accepted?
2) IBC 706.2 requires structural stability to the extent that the wall will not collapse if the building on either side collapses. Each facing wall on either side of the gyp layers and H studs is connected by "melt-away" clips, which under fire conditions will allow separation, but if the building on one side collapses without enough heat/fire to melt them then they might not separate from the gyp and potentially pull the wall down, and the door with it. 706.2 issues the directive only for "collapse", not necessarily from fire, though the commentary in the 1st sentence does. Even then, if a fire on one side of the room caused the structure to pull away, the collapse might technically be "from fire conditions", even without the heat that could cause the clips to deform and separate.

So in order for this assembly to be a fire wall it would need to be:
-706.2 structurally stabile so as to remain upon collapse
-706.3 be of non-com materials unless type V
-706.4 be of a fire resistive rating per t706.4
-706.5 through 706.6 demonstrate continuity
-706.8 have opening protectives (that remain in place) per 716
-706.9 through 706.11 have proper joints, penetrations and duct openings

For a single fire wall with facing walls, 706.2 and 706.8 have me wondering. But if it is a double fire wall, is our only option NFPA 221?

 

[steveray]

I have not heard the term "facing" walls, but that is the gist of the questions I have. If it is not a double wall then a single opening is permitted but only if the opening protective remains in place upon loss of one of the facing walls, assuming the actual fire resistive layer (2-1" gyp panels) remains in place. So if this is the case I have a couple questions:

1) The only place I have seen details for hanging (for lack of a better term) the door and frame from the gyp, and supporting the door and frame on the gyp below is via an ASW, which technically doesn't allow openings (and isn't specifically covered by the code), so do the H-studs and gyp carry the load from top to bottom independent of any support from the facing walls? I have seen a "portal" concept, approved by AMMR twice before, and written about by RLGA, but outside of that is there some method by which this is accepted?
2) IBC 706.2 requires structural stability to the extent that the wall will not collapse if the building on either side collapses. Each facing wall on either side of the gyp layers and H studs is connected by "melt-away" clips, which under fire conditions will allow separation, but if the building on one side collapses without enough heat/fire to melt them then they might not separate from the gyp and potentially pull the wall down, and the door with it. 706.2 issues the directive only for "collapse", not necessarily from fire, though the commentary in the 1st sentence does. Even then, if a fire on one side of the room caused the structure to pull away, the collapse might technically be "from fire conditions", even without the heat that could cause the clips to deform and separate.

So in order for this assembly to be a fire wall it would need to be:
-706.2 structurally stabile so as to remain upon collapse
-706.3 be of non-com materials unless type V
-706.4 be of a fire resistive rating per t706.4
-706.5 through 706.6 demonstrate continuity
-706.8 have opening protectives (that remain in place) per 716
-706.9 through 706.11 have proper joints, penetrations and duct openings

For a single fire wall with facing walls, 706.2 and 706.8 have me wondering. But if it is a double fire wall, is our only option NFPA 221?

UL calls it the "protected" wall

 

[steveray]

And then this:

 

[steveray]

IBC 706.2 requires structural stability to the extent that the wall will not collapse if the building on either side collapses. Each facing wall on either side of the gyp layers and H studs is connected by "melt-away" clips, which under fire conditions will allow separation, but if the building on one side collapses without enough heat/fire to melt them then they might not separate from the gyp and potentially pull the wall down, and the door with it. 706.2 issues the directive only for "collapse", not necessarily from fire, though the commentary in the 1st sentence does. Even then, if a fire on one side of the room caused the structure to pull away, the collapse might technically be "from fire conditions", even without the heat that could cause the clips to deform and separate.

It's anyone's guess as to whether or not any of it really works....Really the intent is to not have a catastrophic failure where the wall wipes out building B or allows the fire to run rampant in to building B....