Fire barrier head of wall detail in wood construction

[architect629]

We do a lot of projects that are sprinklered but still require separation of incidental uses with a 1 hour fire barrier, per 2018 IBC Section 509. We've done a handful of fit outs in single story unprotected combustible type IIIB or VB buildings. We've always directed the contractor to extend the fire barrier to the underside of the roof sheathing (per IBC 707.5), fire stop the joint between the wall and roof, and fire stop any penetrating wood structural members. I know there is no UL assembly for this condition, but an AHJ or inspector has never raised an issue with this approach.

We're now working on a new project in a 5B building and GC is giving us push back to this approach. I reached out to Hilti for an engineering judgement, and they can only provide a firestop joint detail with a 1 hour F rating if the roof/ceiling assembly is also fire rated. We can provide a rated roof/ceiling assembly, and based on 509.4.1 (below), I don't believe we need to rate the entire supporting structure of the roof. We've just never been required to do this before.

Does anyone else have experience with this kind of condition? How are you addressing joint condition between a rated wall assembly and a wood roof/floor construction?

509.4.1​

Where Table 509.1 specifies a fire-resistance-rated separation, the incidental uses shall be separated from the remainder of the building by a fire barrier constructed in accordance with Section 707 or a horizontal assembly constructed in accordance with Section 711, or both. Construction supporting 1-hour fire barriers or horizontal assemblies used for incidental use separations in buildings of Type IIB, IIIB and VB construction is not required to be fire-resistance rated unless required by other sections of this code.

 

[RLGA]

Section 715.1 only requires fire-resistive joints between fire-resistance-rated assemblies. The roof is not required to be fire-resistance-rated since 509.4.1 only requires separation from the remainder of the building, and the roof only separates the building from the exterior. Since the roof is not required to be fire-resistance-rated, the joint between the roof and the fire barriers is not required to be protected.

If you are concerned about the passage of smoke, you can provide sealant at the joint on both sides to minimize leakage.

However, the bottom line is this: If the drawings show a fire-resistive joint there, and the contractor bid on those drawings and has the contract, they are obligated to provide what the contract drawings show. The contractor should give the owner credit if you decide not to have fire-resistive joints at those locations.

 

[steveray]

I think the problem here is twofold.....The penetrating joists, which there is no listed assembly for, and then the joint at the "deck"?

715.3 Fire-resistance-rated assembly intersections. Joints
installed in or between fire-resistance-rated walls, floor or
floor/ceiling assemblies and roofs or roof/ceiling assemblies
shall be protected by an approved fire-resistant joint system
designed to resist the passage of fire for a time period not
less than the required fire-resistance rating of the wall, floor
or roof in or between which the system is installed.

 

[architect629]

Thanks RGLA. What about Section 707.9 which calls for voids between a fire barrier and non-rated roof assembly to be filled with an approved material or system? It was my understanding that UL continuity head of wall details were to be used in these situations since it needs to be an "approved material or system". Those UL details all have rated joints, but there are none for wood construction. IBC doesn't say the joint needs to be rated, it just needs to "retard the passage of fire and hot gases", so I guess fire caulk between the wall and sheathing would do the trick.

707.9 Voids at Intersections​

The voids created at the intersection of a fire barrier and a nonfire-resistance-rated roof assembly or a nonfire-resistance-rated exterior wall assembly shall be filled. An approved material or system shall be used to fill the void, and shall be securely installed in or on the intersection for its entire length so as not to dislodge, loosen or otherwise impair its ability to accommodate expected building movements and to retard the passage of fire and hot gases.

 

[RLGA]

The section refers to voids. If your top plate is tight to the deck, you really do not have any voids. To ensure no gaps are created, you can place a mineral wool strip between the top plate and the deck to provide a flexible seal to close the gap. You only need an "approved" material as a minimum. Get the inspector's approval of the mineral wool strip; that may be all you need.