Corridor Ceiling Rating

[rosegamble]

Hello All!

I am aware of how to get to the required fire partition rating for a corridor wall between dwelling units in an R-2 setting (VB)... 420.2 and 708.3 from the IBC. However, how are you all arriving at the rating of the ceiling in the corridor? Let's say there are dwelling units directly over the corridor. The corridor is part of the exit access system.

Supporting construction for these fire partitions is not required to be rated per 2021 IBC 708.4.1, but I'm talking specifically just about the ceiling itself.

Thanks!

 

[walker.t]

how are you all arriving at the rating of the ceiling in the corridor?

Per 708.4 Point 2, the fire partitions may terminate at a floor/ceiling assembly with a rating not less than that of the fire partition.

 

[Yikes]

Out here in California, we modified IBC Table 1020.2 to require all corridors serving an R occupant load of 10 or more to be one hour rated (and sprinklered).
So both corridor walls and ceiling are at least one hour rated, regardless of what is located above the corridor.

 

[rosegamble]

Thank you both. So in the typical IBC, there is no requirement to rate the R-2 corridor ceilings (even if there is a unit directly above the corridor?). But it comes down to how to address the continuity requires of these fire partition walls around the corridor (708.4).

 

[walker.t]

Thank you both.

You’re welcome.

So in the typical IBC, there is no requirement to rate the R-2 corridor ceilings (even if there is a unit directly above the corridor?)

I disagree with that because the corridor walls need a 0.50-hour rating per Table 1020.2 (Corridor Fire-Resistance Rating) unless your occupant load is 10 or less. Is there another exception I’m missing?

how to address the continuity requires of these fire partition walls around the corridor (708.4)

What is your concern about the continuity of the corridor walls?

 

[rosegamble]

I think Table 1020.2 addresses the walls (fire partitions) around the corridor only, not the ceiling. Or else why would 708.4 Point 1 exist (which allows fire partitions ratings to die at the floor sheathing above, not the bottom of a rated ceiling)?

 

[walker.t]

I think Table 1020.2 addresses the walls (fire partitions) around the corridor only, not the ceiling.

I guess that’s one way to look at it but Table 1020.2 doesn’t specifically say the rating is only for walls.

When we go back to 1020 Corridors > 1020.2 Construction…

2021 IBC 1020.2 Construction
Corridors shall be fire-resistance rated in accordance with Table 1020.2. The corridor walls required to be fire-resistance rated shall comply with Section 708 for fire partitions.

…we then have to go to 708 Fire Partitions > 708.4 Continuity which tells us where the walls have to terminate, ultimately leading to Point 2 which gives us the option to terminate the fire partition at the underside of a ceiling with a rating matching the fire partition walls.

Or else why would 708.4 Point 1 exist (which allows fire partitions ratings to die at the floor sheathing above, not the bottom of a rated ceiling)?

Good question, I don’t know the answer to that. Seems like doing so compromises the protection of the corridor.

 

[rosegamble]

Exactly. I think it would be reaching to assume 1020 applies to ceilings... then does it apply to the floor of the corridor too? Slippery slope. I read the commentary for 1020.2 and it's not any clearer.

I've reached out to my AHJ to get his thoughts!

 

[Paul Sweet]

IBC 420.3 requires floor assemblies in Group R to comply with 711.

IBC 711.2.4.3 requires a 1 hour rating. The exception allows it to be reduced to 1/2 hour if the building has a NFPA 13 (not 13R or D) sprinkler system.

 

[rosegamble]

Thanks. My take is IBC 420.3 requires floor assemblies in Group R to comply with 711 only when the code says it does: when the floors separate dwelling units and when the floors separate dwelling units from other occupancies contiguous to them. My question is about a corridor ceiling. A corridor is considered R-2 occupancy when it serves R-2 units, not a new occupancy. The ceiling doesn't separate dwelling units.

It's easy enough to rate the ceiling in the corridor but I'd like to understand where the code says I need to. Again, why would 708.4 Point 1 exist if the corridor ceiling had to be rated (which allows fire partitions ratings to die at the floor sheathing above, not the bottom of a rated ceiling)?

 

[Yankee Chronicler]

Thanks. My take is IBC 420.3 requires floor assemblies in Group R to comply with 711 only when the code says it does: when the floors separate dwelling units and when the floors separate dwelling units from other occupancies contiguous to them. My question is about a corridor ceiling. A corridor is considered R-2 occupancy when it serves R-2 units, not a new occupancy. The ceiling doesn't separate dwelling units.

It's easy enough to rate the ceiling in the corridor but I'd like to understand where the code says I need to. Again, why would 708.4 Point 1 exist if the corridor ceiling had to be rated (which allows fire partitions ratings to die at the floor sheathing above, not the bottom of a rated ceiling)?

Are you asking about a rated ceiling, or a rated floor-ceiling assembly?

They are not the same -- which far too few architects understand.

 

[rosegamble]

Are you asking about a rated ceiling, or a rated floor-ceiling assembly?

They are not the same -- which far too few architects understand.

I am asking if the floor-ceiling assembly over a corridor has to be rated. A rated ceiling implies just the membrane on the underside, right? Most UL details for rated floor-ceiling assemblies get their rating from the ceiling membrane mostly (e.g. Type X) so it often conflates.

708.4 addresses continuity of fire partitions such as corridor walls. It allows per (1) for the fire partition to extend to the underside of the floor sheathing in the floor assembly above, where none of the floor-ceiling assembly in question is rated.

Why would this option exist if the floor-ceiling assembly over a corridor has to be rated?

(2) addresses the alternative which is just a rated floor-ceiling assembly over the corridor. In this case the fire partition can die at the ceiling membrane of the rated floor-ceiling assembly.

 

[rosegamble]

From the commentary for 708.4(1):

 

[Yikes]

I think 1020.2 describes the entire corridor envelope rating, including the floor below (if on an upper floor), the corridor walls, and the corridor floor-ceiling (if there's another floor above).

IBC chapter 7 describes 3 different types of fire protection walls: fire walls, fire barriers, and fire partitions. 1020.2 clarifies that the intended protection is for fire partitions.

I think Table 1020.2 addresses the walls (fire partitions) around the corridor only, not the ceiling. Or else why would 708.4 Point 1 exist (which allows fire partitions ratings to die at the floor sheathing above, not the bottom of a rated ceiling)?

Speculation on my part, fee free to critique.
One example would be on a two story Type V-B building where the two stories are atmospherically interconnected to each other (via an open stairwell, for example). In that scenario, the single "corridor" atmospheric space is actually 2 stories tall, as indicated by the blue arrows below



However, if there was a unit above the ground floor corridor, then the overall requirement for one hour (or 1/2 hour) corridor construction comes into play, to separate the corridor atmosphere from the dwelling unit atmosphere.

 

[walker.t]

It's easy enough to rate the ceiling in the corridor but I'd like to understand where the code says I need to.

The answer to this is the easy part:

Per 708.4 Point 2, the fire partitions may terminate at a floor/ceiling assembly with a rating not less than that of the fire partition.

Again, why would 708.4 Point 1 exist if the corridor ceiling had to be rated (which allows fire partitions ratings to die at the floor sheathing above, not the bottom of a rated ceiling)?

The answer to that is easy to state, but it’s hard to take: We don’t have to understand the reasoning, it is what it is. “Enquiring minds want to know,” but at the end of the day they don’t owe us an explanation. And I’m in the group that would like to understand the whys behind the whats, I’m learning that I just have to accept some things without knowing the reasons they are the way they are.

 

[rosegamble]

I'm still not following why everyone is ignoring Option 1 and focusing on Option 2. For example, fire barriers can die in the same way right? At the sheathing (VB so wood) of an unrated ceiling assembly above? 707.5.

 

[Yikes]

I'm still not following why everyone is ignoring Option 1 and focusing on Option 2. For example, fire barriers can die in the same way right? At the sheathing (VB so wood) of an unrated ceiling assembly above? 707.5.

I responded with an example in post #14.

 

[rosegamble]

I responded with an example in post #14.

Yes you did -- thank you! But that seems like such a nuanced situation. It's a boilerplate requirement for fire barriers (unlike fire partitions) so it seems like it would apply to other scenarios beyond that very specific one. For fire barriers, it's the same thing right? They can terminate at the underside of the sheathing of a non-rated assembly.

 

[Paul Sweet]

IBC 420.3 "Floor assemblies separating dwelling units in the same buildings, floor assemblies separating sleeping units in the same building and floor assemblies separating dwelling or sleeping units from other occupancies contiguous to them in the same building shall be constructed as horizontal assemblies in accordance with Section 711."

A corridor would be another occupancy contiguous to a dwelling unit above (or below) it.

 

[rosegamble]

IBC 420.3 "Floor assemblies separating dwelling units in the same buildings, floor assemblies separating sleeping units in the same building and floor assemblies separating dwelling or sleeping units from other occupancies contiguous to them in the same building shall be constructed as horizontal assemblies in accordance with Section 711."

A corridor would be another occupancy contiguous to a dwelling unit above (or below) it.

In all the buildings I've worked on the corridor is considered the same R-2 occupancy as the units. What occupancy would you call a corridor if you disagree?

 

[Yankee Chronicler]

There is a hierarchy at work here. A fire barrier is considered to provide a higher level/degree of fire protection/separation than a fire partition. As a result, the provisions for continuity are different.

The general rule for fire barriers is that they must continue through ceiling cavities and terminate against the underside of the roof or floor deck above -- even if there is a rated floor-ceiling assembly.

See IBC Commentary Figure 707.5

Fire partitions, on the other hand, may terminate against the underside of the deck above OR against a rated floor-ceiling or roof-ceiling assembly.

See IBC Commentary Figures 708.4.1 and 708.4.2

 

[rosegamble]

There is a hierarchy at work here. A fire barrier is considered to provide a higher level/degree of fire protection/separation than a fire partition. As a result, the provisions for continuity are different.

The general rule for fire barriers is that they must continue through ceiling cavities and terminate against the underside of the roof or floor deck above -- even if there is a rated floor-ceiling assembly.

See IBC Commentary Figure 707.5

Fire partitions, on the other hand, may terminate against the underside of the deck above OR against a rated floor-ceiling or roof-ceiling assembly.

See IBC Commentary Figures 708.4.1 and 708.4.2

Right. So it the option exists to terminate a fire barrier such as that around a corridor in an R-2 setting by carrying it up to the underside of the deck (non-rated), then why would the ceiling of the corridor need to be rated?

 

[Yankee Chronicler]

As a termination of a fire partition, the corridor ceiling would not have to be rated.

If another provision of the code requires that stories be separated by rated construction, or if the plan of the story above doesn't superimpose corridors and there's a dwelling unit over the corridor, then the floor-ceiling assembly would have to be rated for reasons unrelated to the termination of the fire partition.

Don't conflate code sections.

 

[rosegamble]

As a termination of a fire partition, the corridor ceiling would not have to be rated.

If another provision of the code requires that stories be separated by rated construction, or if the plan of the story above doesn't superimpose corridors and there's a dwelling unit over the corridor, then the floor-ceiling assembly would have to be rated for reasons unrelated to the termination of the fire partition.

Don't conflate code sections.

I agree. Just haven't found the section of the code that requires the corridor ceiling to be rated yet as I don't believe a corridor is a different "occupancy" per the code definition of occupancy (IBC 420.3) and I think the Table 1020.2 only relates to walls when I read my commentary. Still waiting to hear back on the AHJ's thoughts.