Double fire wall opening protective t716.1(2)

[Sifu]

For a double fire wall, per the 2021 IBC and 2021 NFPA 221. Given a required 2-hr fire wall, with the option to construct 2 1-hr walls. A proposal for 2 1-hr walls constructed so that their is a single opening not supported by either wall so that either wall could collapse and the door would remain. 2021 IBC t716.1(2) incudes a new line for NFPA 221 fire walls, which indicates a single opening protective of 1-hr. This is a deviation from NFPA 221 which does not contain opening protectives for a 1-hr fire wall in t4.9.2. (this was acknowledged in the code change reason statement) Does this mean that in a double fire wall, each a masonry wall of 1-hr min., a single 1-hr opening could protect both walls as long as it is not tied to either wall? The DP is calling this a masonry portal wall. I have not seen details as this is a question during the design phase, but I am imagining a steel frame constructed to be independent of both masonry walls, with a 1-hr opening that remain in place if either wall doesn't. I just want to make sure as this is a departure from NFPA 221 and a recent code change.

I have seen wood frame details for this, never masonry.

 

[Tim Mailloux]

I would love to see the details for what the DP is proposing.

 

[Yankee Chronicler]

Where does the 2021 IBC allow two 1-hour walls to be substituted for a single 2-hour fire wall?

 

[Yankee Chronicler]

Found it: IBC 706.2.

My interpretation of NFPA 221 is that any double-wall fire wall only requires a single opening protective. This isn't made clear in NFPA 221, but the row in IBC Table 716.1(2) clearly calls for only a single door, with a rating of 1-hour.

So far, so good. But I see nothing in the IBC or in NFPA 221 that says one side of a double-wall fire wall can collapse. The two 1-hour assemblies constitute a single fire wall with a fire-resistance rating of 2-hours. The definition of "fire wall" in the IBC hasn't changed in years:

[BF] FIRE WALL. A fire-resistance-rated wall having
protected openings, which restricts the spread of fire and
extends continuously from the foundation to or through the
roof, with sufficient structural stability under fire conditions
to allow collapse of construction on either side without
collapse of the wall.

If half of the fire wall collapses before 2 hours have expired, the assembly isn't a 2-hour fire wall.

 

[Jay Smith]

If a single 1-hour door can protect the opening through a double fire wall with a combined 2-hour rating, this would seem inconsistent with 705.3 Exception 2, where the code requires a 1.5-hour rating and specifies which wall gets the rated door. Conceptually, the proposed masonry portal seems like a single fire wall, required to be 2-hour rated with a 1.5-hour door.

I’m not claiming to know the answer to the question or the intent of the code, though. Just saying how it looks from the viewpoint of this one architect (me).

 

[Yankee Chronicler]

If a single 1-hour door can protect the opening through a double fire wall with a combined 2-hour rating, this would seem inconsistent with 705.3 Exception 2, where the code requires a 1.5-hour rating and specifies which wall gets the rated door. Conceptually, the proposed masonry portal seems like a single fire wall, required to be 2-hour rated with a 1.5-hour door.

I’m not claiming to know the answer to the question or the intent of the code, though. Just saying how it looks from the viewpoint of this one architect (me).

Irrelevant. That's not discussing an opening through a fire wall, it's discussing exterior walls of two separate buildings. That's addressing a very specific situation where an S-2 parking garage building is erected immediately abutting an R-2 building. That's not an opening through a fire wall. What that exception is doing is providing that the burden of protecting the opening(s) is to be entirely on the S-2 building, without requiring opening protectives for the R-2 building.

Commentary:

Exception 2 takes into account a practical design
issue.
The great majority of multifamily projects are being
built with parking garages beside apartment buildings.
Access from the parking garage into the apartment
unit’s floor is provided at each garage floor onto the
apartment’s floor for convenience as well as for safety
for the apartment dwellers. Many designs have one or
more of the exterior walls of the parking garage and
the apartment building at a 0-foot fire separation distance.
The requirements within Table 705.8 would prohibit
any openings in these exterior walls between the
parking garage and the apartment building. Based on
the protection afforded by the sprinkler system in the
R-2 use and the inherent fire safety of the parking
garage, this exception would allow these openings.
See Commentary Figure 705.3 for an illustration of this
condition.

 

[Sifu]

I think the idea is that the two 1-hr fire walls serve the purpose while both buildings stand. Then if one goes down, the remaining 1-hr wall is now a 1-hr rated exterior wall. The operative word is think. Which is why I am seeking expert input. In a standard 1 wall configuration, the theory is the wall will not collapse if either side fails, so the 1 1/2-hr door won't either. But in that collapse, the single wall would now be a 2-hr wall with 1 1/2-hr openings as an exterior wall. So I guess I am wondering why a single wall would require 1 1/2-hr opening but the double wall only 1-hr if they are now serving the same function. It is the reduction in fire rating for the single door I am puzzled by. The proposal reasoning doesn't really answer this for me. And since the NFPA....the author of the entire concept, does not reduce the rating I have to wonder about this. Conceptually, if my theory is correct, the exterior wall formed by the loss of the adjacent building would typically be 1-hr at most, so 1-hr remaining opening makes sense. What confuses me is why a 1-hr opening while both buildings are still standing is adequate

As far as details, I too anticipate them, as long as conceptually it works. The wood frame designs employing these 221 walls has been independent frame walls, with melt-away clips secured to an inner fire core. The single door is supported by the shaft liner walls, not either framed wall. The Wood Book has some illustrations. So I assume a steel frame will be independently supported from the foundation, the "portal", and the surrounding CMU walls will not be tied to it.

 

[steveray]

IMO...You go with NFPA OR IBC...You don't dance back and forth.....I have only looked at 221 once and don't remember the nuances other than it just seemed dumb to build 2 walls....

 

[Jay Smith]

Irrelevant. That's not discussing an opening through a fire wall, it's discussing exterior walls of two separate buildings. That's addressing a very specific situation where an S-2 parking garage building is erected immediately abutting an R-2 building. That's not an opening through a fire wall. What that exception is doing is providing that the burden of protecting the opening(s) is to be entirely on the S-2 building, without requiring opening protectives for the R-2 building.

Commentary:

When you wrap a Type V apartment building around a Type II garage on the same lot, the code would typically require a 2-hour fire wall. Section 705.3 Exception 2 allows for an option to replace that with two exterior walls and requires only one rated door in an opening through both walls. I think it’s a relevant comparison. The required rating of the door there makes sense at 1.5-hour. It’s the same as it would’ve been with the fire wall. The door being discussed here at 1-hour seems inconsistent.

 

[Sifu]

IMO...You go with NFPA OR IBC...You don't dance back and forth.....I have only looked at 221 once and don't remember the nuances other than it just seemed dumb to build 2 walls....

Yes, going with IBC, but must use the NFPA as the referenced code. It seems the IBC "added" to the NFPA where it felt the NFPA was lacking. Just trying to confirm the theory behind it.

 

[Jay Smith]

Yes, going with IBC, but must use the NFPA as the referenced code. It seems the IBC "added" to the NFPA where it felt the NFPA was lacking. Just trying to confirm the theory behind it.

This from Steel Door Institute claims two doors are required:

Double Fire Wall Configurations - Steel Door Institute

Sometimes two buildings have a shared wall (“double wall”). This is most common is multi-tenant housing, but can be found in some other building types as well.

steeldoor.org

 

[Sifu]

This from Steel Door Institute claims two doors are required:

Double Fire Wall Configurations - Steel Door Institute

Sometimes two buildings have a shared wall (“double wall”). This is most common is multi-tenant housing, but can be found in some other building types as well.

steeldoor.org

Yes, but the IBC table seems to indicate a single door, however to me it isn't perfectly clear whether they mean EACH wall is required to have a 1-hr door, or a single door of 1-hr. I think a single door makes sense if it is constructed to remain in place, but can't figure out why a single door would have a reduce fire resistance rating, so I question the idea that the table is indicating a single 1-hr door. Maybe a technical opinion is warranted.

 

[Yankee Chronicler]

Yes, but the IBC table seems to indicate a single door, however to me it isn't perfectly clear whether they mean EACH wall is required to have a 1-hr door, or a single door of 1-hr. I think a single door makes sense if it is constructed to remain in place, but can't figure out why a single door would have a reduce fire resistance rating, so I question the idea that the table is indicating a single 1-hr door. Maybe a technical opinion is warranted.

The IBC Commentary is clear that only one fire door is required. I didn't reproduce the illustration that accompanies 705.3. Here it is:


BUT ... this is a specific condition, applicable only to a parking garage abutting an R-2. And the exception is talking about two buildings with a zero fire separation distance. For an interior fire wall with no fire separation distance as a consideration, I can't see any practical reason for building two walls where only one wall is required.

 

[Sifu]

I sent in a request for an opinion to see if they can shed light on it.

 

[steveray]

I don't see anything in NFPA 221 that really talks about the "additive" rating under double fire walls...Maybe it is somewhere else?​

706.2​

Fire walls shall be designed and constructed to allow collapse of the structure on either side without collapse of the wall under fire conditions. Fire walls designed and constructed in accordance with NFPA 221 shall be deemed to comply with this section.

Exception: In Seismic Design Categories D through F, where double fire walls are used in accordance with NFPA 221, floor and roof sheathing not exceeding 3/4 inch (19.05 mm) thickness shall be permitted to be continuous through the wall assemblies of light frame construction.


6.5* Double Fire Walls.

6.5.1 A double fire wall shall consist of two back-to-back walls.

6.5.2 There shall be no connections, other than to the flashing, between the walls.

6.5.3 Each fire wall shall be supported laterally by the building frame on its respective side and shall be independent of the fire wall and framing on the opposite side.

6.10.3* Double Fire Walls.

6.10.3.1 Openings in double fire walls shall be protected using one fire door assembly in each separate wall.

6.10.3.2 Where required for egress, fire door assemblies in double walls shall be installed in accordance with 5.8.3.2.

 

[steveray]

 

[Yankee Chronicler]

There is a bit of a linguistic disconnect between the NFPA double fire wall language and the IBC definition. The IBC requirement for a fire wall (as opposed to a fire barrier) is that the fire wall must remain intact if the construction on either side [but not both sides] collapses. The IBC now introduces into the table a recognition of an NFPA 221 double fire wall, but there is no IBC definition of a double fire wall.

So is an NFPA 221 double fire wall a single fire wall, or is it two fire walls with zero fire separation? From the sections steveray has copied, it appears that the NFPA regards a double fire wall as two fire walls, with the supposition that if the structure on one side collapses in a fire it can take down that half of the double wall, leaving the "other" fire wall and structure intact. I guess the assumption is that in a fire if it takes an hour for the first side to collapse, myou're left with a complete 1-hour assembly still protecting whatever is inside the non-fire side. When viewed in that light, it seems to me that the only reasonable supposition is that each wall has to have a fire door in it -- akin to the communicating doors we sometimes see in hotels between adjoining rooms.

So then we get to the opening question: the designer wants to use the two fire walls, but use a single fire door that is structurally independent from both walls. That would (in theory) allow the opening protective to remain if the building on either side collapses. But if the door ratings in the IBC opening protective table call for 1-hour in what is supposed to be a 2-hour fire wall, based on the expectation that it's actually going to be TWO 1-hour doors, then a single 1-hour door in what is supposed to be a 2-hour fire separation isn't enough. It should be a 90-minuted door, at least.

But I don't see anything in the IBC or in NFPA 221 that seems to allow this so-called "portal."

 

[Sifu]

So then we get to the opening question: the designer wants to use the two fire walls, but use a single fire door that is structurally independent from both walls. That would (in theory) allow the opening protective to remain if the building on either side collapses. But if the door ratings in the IBC opening protective table call for 1-hour in what is supposed to be a 2-hour fire wall, based on the expectation that it's actually going to be TWO 1-hour doors, then a single 1-hour door in what is supposed to be a 2-hour fire separation isn't enough.

It should be a 90-minuted door, at least.

Exactly my question.

But I don't see anything in the IBC or in NFPA 221 that seems to allow this so-called "portal."

Exactly the reason I wonder if I am incorrectly assuming the IBC only requires a single opening for both walls. Unless "portal" is exactly what the code is imagining. I included the proposal for the "portal" strategy in my question, so we'll see what their opinion is.

 

[steveray]

Exactly my question.

Exactly the reason I wonder if I am incorrectly assuming the IBC only requires a single opening for both walls. Unless "portal" is exactly what the code is imagining. I included the proposal for the "portal" strategy in my question, so we'll see what their opinion is.

And don't forget the footnotes:

 

[Sifu]

Clear that each wall is required to be rated 1-hr to replace a single wall. Not clear that each wall gets it's own opening. They clearly use a column heading of "Each wall of the double wall assembly" over the required rating for the double walls. They do not include that above the column for the fire door rating. Seems like that would have been included.


I can't reconcile the reduction from a 1 1/2 rating to a 1-hr rating if it is a single opening as a portal. I also see some viability to a portal if it can be designed to remain in place...with a 1 1/2-hr door.

I did find this in the '21 significant changes book. I added the bold face.

If misapplied, it might be determined that a 3-hour single wall assembly only
requires a 1-1/2 hour fire protection rating for the door and not recognize
that it is the rating needed for the door in each of the two adjacent
fire walls.

Anyway, I asked for a technical opinion, which should help.

 

[Yankee Chronicler]

I agree that the way the table is structured doesn't make that clear. The way I analyzed (or "rationalized") it is as follows:

We're using two 1-hour walls to do the job of one 2-hour wall. So we want the non-fire side to be protected for two hours.

If we have two 1-hour walls with an opening through both, and the structure and the 1-hour rated wall on the fire side are allowed to collapse, we expect that the collapse could occur any time after 1-hour. If there's only one door and it happens to be in the wall on the fire side, then when that wall collapses after one hour, the non-fire side is immediately exposed to the fire through the now-unprotected opening in the remaining wall.

Hence, to make this work, it needs a 1-hour rated door in each of the two walls.

The proposed independent "portal" with a single door is an interesting concept, but I don't see how it can be detailed to work, and I also don't see anything in the code that allows it.

 

[Tim Mailloux]

The proposed independent "portal" with a single door is an interesting concept, but I don't see how it can be detailed to work, and I also don't see anything in the code that allows it.

the independent portal is fairly easy to accomplish on the ground level. If the building / fire wall is multiple stories I am not sure how that could be accomplished.

 

[Sifu]

It is on the first floor on a 2-story. I spoke with ICC technical staff and he agreed the code table does intend that each wall have an opening protective, but that it isn't crystal clear. Likely not anticipated, because NFPA prohibits it. As far a portal frame, it may comply with the intent of structural independence if that can be verified, but I would want this through an AMMR, with a 90-min opening min.

 

[Sifu]

It took awhile but here are the details. Still have questions about the openings but they are proposing a 90-min door in the portal frame at least. They have requested an alternate from the CBO for the portal frame concept and the single openings. The plan is to create a double masonry fire wall, and at each opening create a structurally independent portal. Essentially create a single fire wall within the double fire wall for the opening, with a 90-min opening protective. Actually using U904 so each wall is 3 hour.




Now, check out the fire window detail...each has a 1-hr window.




This structure is cut into 3 buildings by these fire walls. The fire walls are swiss-cheezed with openings (they have not provided the opening width calculations but looks to exceed 25%).