Fire partitions continuous to rated ceiling... which then requires otherwise non-rated supporting walls to be fire rated?

[bgadaspen]

Hello,

We are working to better understand the requirements for fire-rated assemblies in a small employee housing building. This group-R3, type VB, NFPA 13D sprinklered building is a single story, slab on grade with pre-engineered gable truss roofs.

We have two conditions where fire paritions are required: at corridors, and where sleeping units abut each other.

Our understanding would be that where these 1 hour fire paritions are required, 708.4 would require that they are continuous to, in our case, a 1 hour rated membrane at the bottom of the truss ceiling.

Where we are hung up is on whether or not all other walls supporting the trusses would then need to be fire rated. Our logic is a follows:
-708.4 requires "The underside of a floor/ceiling or roof/ceiling assembly having a fire-resistance rating that is not less than the fire-resistance rating of the fire partition."
-711.2.3 (supporting construction for horizontal assemblies) requires "The supporting construction shall be protected to afford the required fire-resistance rating of the horizontal assembly supported."

Does the requirement for one wall that must be a fire partition effectively create the requirement that all walls and ceilings on the fire partition separated spaces need be fire rated? Are we missing something here? It seems that the intent is to stop fire from moving from one side of the partition to the other. Why would it matter if the wall on the other side of the room from the partition is fire rated or not? The fire wouldn't make it to that wall due to the fire parition and rated ceiling.

Thank you all.

 

[RLGA]

The requirements for fire-rated corridors state that corridor walls shall comply with the requirements for fire partitions. There is no mention of compliance with horizontal assemblies for corridor ceilings--all you need to provide is a 1-hour assembly, which is typically a layer of 5/8-inch Type X gypsum board on resilient channels or two layers of 5/8-inch gypsum board.

The ceiling of a fire-rated corridor is not a horizontal assembly and is not required to comply with the provisions of Section 711.

 

[steveray]

IF....the walls actually hold up the rating, then they need to be rated so that the ceiling does not collapse before it's time....Not all interior partitions hold up the roof/ ceiling....Typically

 

[redeyedfly]

Typically you

The requirements for fire-rated corridors state that corridor walls shall comply with the requirements for fire partitions. There is no mention of compliance with horizontal assemblies for corridor ceilings--all you need to provide is a 1-hour assembly, which is typically a layer of 5/8-inch Type X gypsum board on resilient channels or two layers of 5/8-inch gypsum board.

The ceiling of a fire-rated corridor is not a horizontal assembly and is not required to comply with the provisions of Section 711.

708.4 Ex. 3 has a requirement for the corridor ceiling depending on how the fire partition is detailed.

Only the load bearing walls supporting the fire rated floor assembly would need to be rated typically. You can't have a 1hr floor supported by 0hr walls. EXCEPT when the floor assembly is in IIB, IIIB, VB and is separating dwelling units per 420.3 which it appears meets your situation.

 

[steveray]

Typically you

708.4 Ex. 3 has a requirement for the corridor ceiling depending on how the fire partition is detailed.

Only the load bearing walls supporting the fire rated floor assembly would need to be rated typically. You can't have a 1hr floor supported by 0hr walls. EXCEPT when the floor assembly is in IIB, IIIB, VB and is separating dwelling units per 420.3 which it appears meets your situation.

Forgot about that...Answering off the cuff....VB for the win....

 

[RLGA]

Typically you

708.4 Ex. 3 has a requirement for the corridor ceiling depending on how the fire partition is detailed.

Only the load bearing walls supporting the fire rated floor assembly would need to be rated typically. You can't have a 1hr floor supported by 0hr walls. EXCEPT when the floor assembly is in IIB, IIIB, VB and is separating dwelling units per 420.3 which it appears meets your situation.

708.4, Exception 2.1, would also work. My response was based on Exception 2.2, but I didn't realize the OP mentioned NFPA 13D as the sprinkler system, which is not allowed for Exception 2.2.

 

[steveray]

It would have to be a pretty big building to have interior bearing walls with roof trusses.....Typically...