Rated "Lid" ?

[lpiburn]

Hello all,

1. Is there such thing as a "rated lid" for non-corridor applications?

2. Are there any exceptions for fire barrier continuity in situations with very high floor-to-deck heights?

It seems like I run into this question on a lot of projects. We have a building with a high roof (typically pre-engineered metal) and a couple of relatively small rated rooms in it. The comment I get is "we'll just put a lid on it", or more accurately "We'll use a rated ceiling so we don't have to run the walls to deck". From all of my research I have found only one instance where this is EVER allowed in code and that is the corridor exception 709.4 Continuity (exception 3). The problem is that only applies to corridors that are allowed to be constructed as fire partitions. I have not found anything where this technique can be used for a rated room such as a >100s.f. laundry room, etc.

The thing is, when I tell people there's no such thing as a fingerquotes "rated ceiling" and start explaining floor-ceiling assemblies and so forth, I either get blank stares or I get replies like "we've been doing that for years and never had a problem." Does a "rated lid" need to be constructed as a full blown floor-ceiling-assembly with a UL listing etc. ? Would this kind of condition have to be specifically approved by the AHJ?

Any help or insight would be appreciated.

-LP

 

[High Desert]

I think what you're referring to would be fir barriers separating certain rooms from other parts of the building, correct? These can be either fire barrier walls or horizonatal assemblies section 707.3.9. the horizontal assemblies (rated lid) are require to be rated for whatever rating the code calls for. so yes, they would have to be a rated horizontal assembly.

 

[steveray]

What code edition are you on?...I believe that requirement has gone away in 2009......the 100 ft of storage piece....

 

[lpiburn]

The project where this currently came up was under 09 IBC but this has come up for various projects under a few different codes. The requrement for "storage rooms" >100s.f. went away, but laundry rooms is still included. Regardless, that is just one example. Does it matter why the room is rated in terms of enclosing it with a lid?

 

[steveray]

If the room actually needs to be rated HD has you on the right path, it can be done with a lid, but it is a listed assembly also.....another design approach would be to run the building as mixed use non seperated....if it works, you don't rate it....most smallish buildings that I have seen work that way....

 

[RLGA]

I would treat it as a floor assembly, even though it will not experience a true floor load. Therefore, as previously mentioned, compliance with Section 712 (2009 IBC) for horizontal assemblies would be applicable.

 

[lpiburn]

I'm still a little confused. Why would a UL tested floor assembly be required for a space where no floor load exists? The corridor exception is pretty clear, "Where the corridor ceiling is constructed as required for the corridor walls, the walls shall be permitted to terminate at the upper membrane of such ceiling assembly. That probably wouldn't stand up to the UL test for horizontal assemblies.

Has anyone here written up a violation (or been written up) for only putting a hard ceiling and not properly rating the room either horizontally or vertically?

 

[globe trekker]

lpiburn,

Have you asked / requested a code section from the RDP to substantiate them

"putting a lid on it"? Request a code section or sections that will allow this,

and see what kind of response you get.

.

 

[RLGA]

Corridors are protected with fire partitions, which are a lower form of fire-resistive construction than the fire barrier. Fire barriers are required to extend to the floor or roof above. Therefore, if you use a tested floor assembly, then the fire barriers can terminate at that horizontal assembly. Even though it has been tested as a floor assembly for fire resistance, it does not need to be structurally designed as a floor.

However, if the space above this "floor" is suitable for a second story, I would design it to support typical floor loads, because you know somebody will later want to make use of that "unused" space. This isn't a requirement, but just a practical observation.

 

[lpiburn]

I'm on the design team, not the AHJ. I serve as our in-house code specialist so these questions tend to come up during design from various other members of the design team. That's usually when I use the phrase "there's no such thing as a rated ceiling" and this discussion gets started. I don't know, maybe my experience is atypical but it seems like putting on a "hard lid" is almost a standard solution for this type of problem. Since I couldn't find anything allowing it I thought it was worth posing here.

 

[lpiburn]

Even though it has been tested as a floor assembly for fire resistance, it does not need to be structurally designed as a floor.However, if the space above this "floor" is suitable for a second story, I would design it to support typical floor loads, because you know somebody will later want to make use of that "unused" space. This isn't a requirement, but just a practical observation.

The ASTM standard on which the UL test is based includes a hydraulic rig imposing a floor load. Here is a video example. A horizontal assembly cannot be tested without being structurally designed as a floor.

 

[RLGA]

The load used in the test may not correspond with what an actual floor load and span would be in the actual situation.

GA-600 has a floor/ceiling assembly, FC 5406, which requires 2x10s at 24 inches on center with 1/2-inch plywood on the top side and two layers of 5/8-inch Type X underneath for a 1-hour assembly. This assembly does not indicate what the maximum floor load this system can support. But, if installed as minimally indicated in the assembly description, the system will provide a 1-hour fire-resistive assembly. Now, the 2x10s at 24 inches o.c. will likely not be suitable for a 15-foot span with a 250 psf live load for a heavy storage use. Thus, the floor is not structurally designed as a floor for actual conditions.

ASTM E 119 and UL 263 require a 12-foot span with "maximum load condition allowed under nationally recognized structural design criteria," whichprovides little information from a structural point-of-view. The UL assemblies also do not indicate what load was applied, so the situation is similar to the GA-600 assembly mentioned above.

 

[cda]

I'm on the design team, not the AHJ. I serve as our in-house code specialist so these questions tend to come up during design from various other members of the design team. That's usually when I use the phrase "there's no such thing as a rated ceiling" and this discussion gets started. I don't know, maybe my experience is atypical but it seems like putting on a "hard lid" is almost a standard solution for this type of problem. Since I couldn't find anything allowing it I thought it was worth posing here.

Rated drop ceiling???

 

[lpiburn]

That makes a certain amount of sense, but the assembly is still "designed as a floor". In the corridor example you could use studs at 24" o.c. with 1/2" gyp top and bottom. That certainly wouldn't cut it as a floor even for a span less than 12 ft. I keep bringing that example up because it relates to the intent and purpose of the exception. For a corridor, you are protecting the inside of the space from fire/smoke intrusion from adjacent spaces. In the case of a rated room, you are preventing the spread of fire from that room to adjacent spaces.

So lets take an extreme example. Say we have a relatively small rated room, perhaps 11'x11'. It happens to be situated under a roof ridge that is 25' above finish floor. If you were to properly rate that room you have two options. One, run the walls all 25' up to the roof deck, which would look more like a chimney than a room. Two, frame out a "second-floor" element per UL (or GA-600 as mentioned above) that is only 11'x11', and put that floor over the rated room.

In the first instance, the walls stop being necessary to contain a fire way before they touch the roof. Containing smoke could be achieved with a minimal ceiling enclosure as long as it is sealed properly. Providing a "lid" similar to the surrounding walls should be more than sufficient to satisfy the intent of the code in preventing the spread of fire and smoke. In the second example, the fire and smoke is definitely contained, but it seems like overkill to provide a walkable surface above the ceiling where there is no purpose to having one.

I suppose this is splitting hairs at this point :banghd but I'm trying to come up with a reasonable response when the question comes to me. Maybe the best response is to have a set of lightweight rated floor assemblies in my pocket to offer as an alternative to a "rated ceiling".

 

[Dr. J]

I agree that “there is no such thing as a rated lid”, and also that “they are used all the time”.

IBC 707 states:

707.5 Continuity. Fire barriers shall extend from the top of the floor/ceiling assembly below to the underside of the floor or roof sheathing, slab or deck above and shall be securely attached thereto.

A “lid” made of drywall and studs (or shaftwall and CH studs) is NOT a floor, roof, slab, or deck. Where is the testing that shows the max span, penetration methods, and other construction details? Just because a gybpd “lid” can be built to span a large room does not mean that it will hold up under fire conditions.

Further, the question of how to penetrate the “lid” will be problematic. Do you use a ceiling damper (UL 555C)? These are only listed for the membrane penetration of a real floor/ceiling assembly and just protect the structure of the floor/ceiling assembly from radiant heat – they are not equivalent to the UL 555 fire damper required in a fire barrier. However, there is no UL555 fire damper tested and listed for use in a horizontal gypbd assembly – horizontal dampers are tested and listed only for concrete floor openings. The exception to allow no damper in a ducted HVAC system in a sprinklered building is assuming a vertical wall –but is a horizontal wall with no damper equivalent to a vertical wall with no damper???? Don’t know, but I would guess not given the direct impact of heated gasses on a ceiling.

Even more fun: Say you do use a real floor ceiling assembly, like RGLA is identifying. Now you have a rated floor penetration, and we all know what it takes to penetrate a floor assembly – a shaft (ok, there are exceptions, but I do a lot of healthcare, and the exception goes away for I occupancies). Even using 716.6.1, a real UL555 fire damper would be required, but as already stated, these are only tested and listed for horizontal concrete openings.

Still having fun: Now that you have a floor/ceiling assembly, is this now a mezzanine? Is it a potential storage area affecting sprinkler coverage or more ratings? Especially in the high-bay space of the OP.

So, since “they are used all the time”, we just make stuff up about them all the time. Once you start making stuff up, where do you stop? You can make up any stuff you want.

 

[High Desert]

HORIZONTAL ASSEMBLY. A fire-resistance-rated floor

or roof assembly of materials designed to restrict the spread

of fire in which continuity is maintained.