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NFPA 221 double fire wall

Sifu

Sifu

SAWHORSE
Joined
Sep 3, 2011
Messages
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I have a proposal to use a double fire wall designed in accordance with NFPA 221 (using the 2021 edition of NFPA 221 and the 2018 edition of IBC). This is acceptable per IBC 706.2. I have researched it and find a few items still unclear. The proposal is to build (2) 2-hr, wood framed walls to separate a type III building requiring a 3-hr wall. Per NFPA 221 this is acceptable. Section 6.2.1 requires that fire walls remain stable after collapse, and that a double fire wall constructed in accordance with section 6.5 meets that stability requirement. As far as I can tell then, each wall meets the stability requirement even though the wall is bearing and connected to the structural framing and supporting floors on each side, and will collapse in a fire event. This is because since there is no connection to the other wall, the 2-hr wall will remain to provide protection to that side of the assembly. Opening protectives (doors) are where I am a little unsure.

Section 6.10.3 requires each wall to have a door. Makes perfect sense, except these doors are for egress in both directions, and are acting as a horizontal exit. Now we have a problem. That is pretty much where the code language ends, and we go to the annex. We end up at A.5.8.4. This section provides an example of how to use a "freestanding" vestibule in figure A.5.8.3(b) when used for egress. Unfortunately, the drawing is pretty basic, and there is no additional information. My understanding of "freestanding" here is that it is independently supported to the foundation (in this case the podium).

My hang up is the "freestanding" part. If the fire wall itself is not freestanding, and allowed to collapse why is the vestibule wall? Does this mean that the square footprint of the vestibule gets supported all the way to foundation or am I misunderstanding this. I am not sure why the door couldn't fall away with the rest of the framing and leave the other door and wall in tact for protection.

I am also looking for confirmation that my understanding of this wood framed, bearing wall that will collapse being acceptable is correct. I think I have that part right...

RLGA wrote an excellent paper on this, and his opinion is that the doors must be independently supported and not connected in any way to the collapsible fire walls. This seems to align with my understanding.

ANY guidance is appreciated, and obviously if RLGA can contribute to verify or refute my understanding I would be forever grateful. This is a challenging condition, and the DP's are just as unsure as I am and are waiting on me to guide them.
 
Not my area,, But put one three hour door in one of the walls??? And call it good??
 
Constructability on those walls will be a nightmare....And how do you rate the penetrations on both ides of the walls once they are built? My opinion is that once the wall collapses, the door is meaningless, but that is not spelled out in code. I would have to see details to make a better assessment...
 
Two doors are definitely required. I think the theory is that if the once wall collapses after the 2-hours, the second wall will last at least the next hour to give the 3-hour protection. IBC t716.1(2) would require a single 3-hour door, but footnote a allows two doors in the same opening to each be 1 1/2-hour....this begs the question; are the two openings in a vestibule 7' apart considered to be in the same opening? But, either way, the 2-hour wall would only require a 1 1/2-hour door anyway. But, in theory, if one side falls away and the remaining wall remains and is acceptable, why does that not count for the door as well? If the wall and door fell away, and left the other wall and door, why is that not acceptable. Instead, my understanding is the walls around the vestibule and door can fall away but the vestibule must remain. I just don't understand! Below are the snips from NFPA 221.

1631199302223.png1631199347768.png
 
According to my research it must be two-hour rated as it will be acting as the fire wall providing the separation.
 
steveray said:
If the one wall falls does it take out the other door or wall? Even if it is structurally independent?
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in a double fire wall design each fire wall has a door in it. If one side collapses the fire wall and door fall, but the other fire wall and door remain. The problem being that this type of door arrangement doesnt work for egress.
 
Just dealt with one that is a big mess....Designer had a good idea of "independently supporting" a single door, but the reality was less than spectacular....
 
Tim Mailloux said:
in a double fire wall design each fire wall has a door in it. If one side collapses the fire wall and door fall, but the other fire wall and door remain. The problem being that this type of door arrangement doesnt work for egress.
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The problem being that this type of door arrangement doesnt work for egress.

Que ? Why?


Depending on occupant load it could,,

If two doors are installed, swinging opposite ways, would work.
 
cda said:
The problem being that this type of door arrangement doesnt work for egress.

Que ? Why?


Depending on occupant load it could,,

If two doors are installed, swinging opposite ways, would work.
Click to expand...
because the two doors are in line with one another.
 
See post #9 in this thread

Fire Wall or Two separate Adjacent Buildings?

2015 IBC Type 2B Construction F-1/S-1/B/A The existing building area is maxed out per Table 506.2 and the owner wants to expand. If my thinking is correct, there are only two options. 1. Add a 3 hour fire wall (Table 706.4), which allows openings between the existing and proposed buildings...
www.thebuildingcodeforum.com

RGLA "How I've addressed this is to create a structural door opening in which its frame has its own structural footings and is not physically connected to either wall. The door must remain in place should either wall collapse."
 
The proposal as it stands now is a vestibule with a double active cross corridor door swinging in both directions so that egress can occur in both directions. The doors will be on mags. The vestibule will be large enough to allow complete opening of each door. The question is about the "freestanding" vestibule. In the other thread referenced by Tim, RLGA provides a path for the independently supported doors, which is in line with the paper he wrote and with my idea of what "freestanding" means in this case. However, I am still failing to find the logic in requiring a "freestanding" (independently supported to foundation) vestibule or doors. If the walls are allowed to fail on one side, why wouldn't the vestibule and door?
 
Sorry. I don't have any drawings to attach as this was shown to me via webex and not submitted.
 
steveray said:
Just dealt with one that is a big mess....Designer had a good idea of "independently supporting" a single door, but the reality was less than spectacular....
Click to expand...
What was the problem?

I did exactly that for a project and it was approved and installed with no issues (at least none that were brought to my attention). Our solution was to design a structure steel door frame with its own foundation system. Between the structural door frame and the two fire walls, we used a fire-resistive joint system. Within the structural door frame, we installed a standard single 1-1/2-hour fire-rated hollow metal door and frame.

To my knowledge, there were no field problems or inspection issues.
 
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In my case, maintaining the rating of the jamb/ installation details, penetration details, joint details, double swinging doors with a smoke seal that becomes an ANSI violation (bottom smooth 10"), and a host of other unseen design issues....
 
So a single opening in between the double fire walls? If I understand correctly, each fire wall must have it's own opening. And for use with egress then a vestibule would be required. In this case a vestibule will be required to allow the double acting doors to open in each direction. Or, did you design two fire walls with a single opening, and only that opening was structurally supported? In that case, if one set of walls failed, the other would still be there, as would the independent door? Doing this eliminates the need for the vestibule, but would seem to contradict the very clear directive that each fie wall have it's own opening. If that is what you did, how did the fire walls terminate at the opening construction? We would have some sort of joint, and the two fire walls would have to connect somehow to form the jamb construction for the independent door, which would negate the independent nature of them.
 
Sifu said:
So a single opening in between the double fire walls? If I understand correctly, each fire wall must have it's own opening.
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Yes to the question. Per NFPA 221, you would be required to have two separate doors either in a vestibule for egress purposes or nearly back-to-back for non-egress openings. My situation was an egress door, but the vestibule option would not work (it was an existing building with an addition--could not get the vestibule to work on the existing building side). However, we submitted a code modification request to the city and it was approved.
Sifu said:
Or, did you design two fire walls with a single opening, and only that opening was structurally supported? In that case, if one set of walls failed, the other would still be there, as would the independent door? Doing this eliminates the need for the vestibule, but would seem to contradict the very clear directive that each fie wall have it's own opening.
Click to expand...
That is what we did. It does contradict NFPA 221, but it was approved through a code modification submitted to the AHJ.
Sifu said:
If that is what you did, how did the fire walls terminate at the opening construction? We would have some sort of joint, and the two fire walls would have to connect somehow to form the jamb construction for the independent door, which would negate the independent nature of them.
Click to expand...
The independent structural steel frame was set in its own concrete foundation and abutted the two masonry walls across the space between the two walls. There was a small gap between the structural steel frame and the masonry, which was protected with a fire-resistant joint system on both sides around the full perimeter of the structural steel door frame. There was no other physical connection between the structural steel door frame and the two masonry fire walls other than the fire-resistive joint. If one wall collapsed, I do not believe the fire-resistive joint material would have enough tensile strength to pull the structural steel frame down with it given that it was embedded in its own foundation. I think we treated the structural steel frame with intumescent fireproofing. Within the structural steel frame, we installed a standard fire-rated hollow-metal door and frame. The hollow-metal door frame was anchored to the structural steel frame, much like it would to the jamb of a door opening in a masonry wall.
 
RLGA, perfect! At least I understand. However, in my case this is all new, so there is not a reason for them to not use a vestibule. If they don't want to I will suggest an alternate request to the CBO be made. I see the logic and viability in your solution. But if they do go the vestibule route, the code language is "freestanding". I am taking this as independently supported, but I can't figure out why. It seems that if one side had half the vestibule and a door, and the other side had half the vestibule and the door, that either side could fail and still leave the other side protected. Or am I reading more into "freestanding" than I should?
 
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