Existing-to-new fire wall interface

[kurt999]

IBC 2018
I realize that I have some continuing confusion with fire walls -- and the door requirements -- between new sprinklered additions and existing unsprinklered buildings.

As an example -- Given a typical project where a fully-sprinklered addition is being connected to an existing unsprinklered building (existing building large enough to have been divided into fire areas).
What is the fire wall requirement at the interface? I think I've assumed that the existing building wall would need to be modified to provide the required 2-hour fire wall resistance and continuity (if not already compliant) -- but what about the new side of things? Does the sprinkler eliminate the need to create a new fire wall as well -- in other words, is a double fire wall required in this case?

Thanks in advance.

 

[Yankee Chronicler]

A double fire wall is an exception. There's a reason why the definition of the term is for "fire wall" -- singular -- and why the code discusses "fire wall" -- singular -- rather than "fire walls" -- plural.

There's more to a fire wall than the rating and the continuity. A fire wall must also be constructed in such a way that the construction on either side can collapse without resulting in the collapse of the fire wall. Trying to take an existing exterior wall (which may or may not be a load-bearing wall) and modify it to be a fire wall can be difficult, and is often impossible.

[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.

 

[RLGA]

I have discussed this situation in other threads before. The existing wall cannot be THE fire wall between the existing building and the addition because of the structural independence provision. Thus, you will need to provide a double fire wall, which NFPA 221 (as referenced by the IBC) addresses.

However, the issue many encounter is how to handle openings. NFPA 221 does not address openings, but it does state that there should be no connections between the walls other than flashing. The explanatory material in Annex A states, "Since there should be no connections between the walls, particular attention should be paid to the details at openings in the walls."

I handled this in the past by creating structural, free-standing door portals that had their own footings. Then, fire-rated frames and doors are installed within these portals. The portals were constructed of thick plate steel and fireproofed (intumescent) with firestop joints between the portal and the two fire walls.

 

[kurt999]

I have discussed this situation in other threads before. The existing wall cannot be THE fire wall between the existing building and the addition because of the structural independence provision. Thus, you will need to provide a double fire wall, which NFPA 221 (as referenced by the IBC) addresses.

However, the issue many encounter is how to handle openings. NFPA 221 does not address openings, but it does state that there should be no connections between the walls other than flashing. The explanatory material in Annex A states, "Since there should be no connections between the walls, particular attention should be paid to the details at openings in the walls."

I handled this in the past by creating structural, free-standing door portals that had their own footings. Then, fire-rated frames and doors are installed within these portals. The portals were constructed of thick plate steel and fireproofed (intumescent) with firestop joints between the portal and the two fire walls.

Thanks for the reply, and I think I'm following your logic -- I don't see a way around the NFPA double fire wall due to 706.2.
So, a follow up question -- the door portals you've used in the past -- how far apart were your fire walls?
The double fire wall condition would need a door in each fire wall, correct? Single high fire rating door in one wall only ever a possibility?
I've seen double fire walls with about a 3" separation space, and then a door in each wall. However, that presents an egress issue in many cases, since they swing in opposite directions. Are we heading toward the need for a 2-hour fire rated vestibule, with 4 feet in front of the door swing?
I'm sure I'm missing something on the acceptable door configuration.

 

[Yankee Chronicler]

Related discussion: https://www.thebuildingcodeforum.co...-fire-wall-opening-protective-t716-1-2.36976/

 

[kurt999]

Related discussion: https://www.thebuildingcodeforum.co...-fire-wall-opening-protective-t716-1-2.36976/

Thanks, Yankee -- I snipped part of what you wrote from the related discussion:

"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."

I do agree that a single door approach in a double fire wall seems like a non-starter in any case -- how does a door-sized hole function in a fire?

The two, 1-hour walls with a rated door in each of the two walls is an interesting approach. I have previously interpreted a 2-hour fire wall requirement as two, 2-hour walls in a existing-to-new scenario -- sounds like I may have misinterpreted this.

I continue to see the "back to back" double wall diagram online -- with minimal space between the walls, connected by flashing only. Do you have any input on the door swing / egress path direction issue that I noted above? I'm having trouble seeing how this doesn't turn into a need for a rated vestibule of some kind in order to accommodate the correct door swing direction.

Thanks for the response and input. Trying to wrap my head around this.

 

[RLGA]

Thanks for the reply, and I think I'm following your logic -- I don't see a way around the NFPA double fire wall due to 706.2.
So, a follow up question -- the door portals you've used in the past -- how far apart were your fire walls?
The double fire wall condition would need a door in each fire wall, correct? Single high fire rating door in one wall only ever a possibility?
I've seen double fire walls with about a 3" separation space, and then a door in each wall. However, that presents an egress issue in many cases, since they swing in opposite directions. Are we heading toward the need for a 2-hour fire rated vestibule, with 4 feet in front of the door swing?
I'm sure I'm missing something on the acceptable door configuration.

Both fire walls were masonry (a 2-hour fire wall was required). The steel plate portal spanned the gap between the two plus some overlap into both walls to allow the installation of the firestopping. A single door frame and door complying with Table 716 (90-minute rating) was installed within the portal. The portal had no connection to either fire wall other than the firestopping, and it was supported by its own footings.

Using two doors inline with each wall means the opening cannot be used for egress (especially if the occupant load is greater than 50) or on an accessible route.

 

[steveray]

Are you over area requirements or changing construction type? Why do you need a fire wall?