Floor dampers

[Sifu]

Given a 1-hr floor ceiling assembly an a VB, R2, consisting of gypsum panel on the bottom, open web floor truss, 3/4" subfloor, and gypcrete floor surface.

Each unit has an air handler within the unit. The steel ducts run down from the unit into the rated floor system and supply the unit air conditioning through the floor. So no through penetrations of the FC assembly, but a top membrane penetration of the FC assembly. Each unit is isolated with its own air handler and duct system so no communication with other units. A question has come in that makes me scratch my head. "Are floor dampers required?". When I look to the 2018 IBC I can find nothing that specifically addresses a membrane penetration of the floor surface. Most sections appear to be not applicable, some such as 714.6.2 would appear to permit the membrane penetration since it does not connect any stories. Section 717.6 only addresses the ceiling membrane of the assembly. I'm not sure I have ever heard of a floor register damper but I'm also not sure a damper couldn't be installed in the floor surface. I have just never had to address this.

The floor system requires gypcrete as the floor surface as part of the assembly. The gypsum panels on the ceiling side of the assembly are not penetrated, only the subfloor and gypcrete. The question pertains to interrupting the rated assembly. The questioner says the tested FC assembly makes no mention of openings, penetrations or dampers. 714.5.2 tells us that recessed fixtures can't reduce the rating of the assembly and sends us back to 714.5.1.1 & 714.5.1.2 which only address through penetrations. Neither seem applicable.

I am having trouble identifying the hazards. In a 1-hr FC assembly, would fire and smoke travel down into the steel ducts and then back up into the air handler, and spread the fire from to unit to the same unit? Is there a concern the fire and smoke will escape the duct and get into the floor system and compromise the structure within the 1-hr time frame? Or, is this not addressed because there isn't enough hazard to worry about?

When I am asked these questions I look at them from a comment writing perspective. I cite a code requirement. I'm not sure I can find one here.

 

[mtlogcabin]

Given a 1-hr floor ceiling assembly an a VB, R2, consisting of gypsum panel on the bottom,

Look at the floor ceiling listed assembly. I bet the fire rating is from the ceiling side only and no rating is applied to the fire side.

 

[Sifu]

Look at the floor ceiling listed assembly. I bet the fire rating is from the ceiling side only and no rating is applied to the fire side.

It has been discussed on the forum before in other threads with the same conclusions. I don't know the exact system they are using but the questioner said that it was not designated as that was my first thought. As RLGA has previously educated me, ASTM E 119 says the systems are tested from the bottom side. I am trying to reconcile the listed assembly that includes flooring with the belief that any of the elements could be eliminated unless shown as optional.

BXUV very clearly says the ratings apply to the assemblies in their entirety. ASTM E 119/UL 263 clearly says they aren't tested from the top. So even if the test method does not include exposure from the top, do I get to just eliminate a portion of the system when it is part of the tested assembly? This is my dilemma (really his dilemma but I try to take advantage of any educational opportunity I can find).

 

[steveray]

do I get to just eliminate a portion of the system when it is part of the tested assembly?

No

 

[steveray]

As you do not meet any of the 8 prescriptive exceptions of 714.5.2, it kicks you back to 714.5.1.1 or 714.5.1.2....And treat it like a through penetration...Juist the top side of a through penetration IMO, but nonetheless...

 

[Sifu]

Those sections are for through penetrations, but I understand the membrane gets protected as though it were a through penetration. However I don't think a through penetration firestop assembly could be used for a membrane penetration by a duct. Besides, and I really don't want to open this can of worms,...is a duct a penetration? If we read about "openings" in 712 we see 712.1.6 which is specific to ducts and transfer openings. That sends us directly to 717, which covers membrane "penetrations" by ducts. Even though I think the code is sloppy in its approach to the language of "penetrations" and "openings" I think the specifics located in 712.1.6 and 717.6.2 for ducts and air transfer openings would be more applicable than the penetrations in 714.

I admit I am seeking some confirmation bias in my thinking. I am thinking if the assembly isn't tested from above then the rating comes from the tested side, which is where the protection would be required. I am also thinking that there is little hazard from a floor membrane opening to the required 1-hr rating of the assembly. Maybe I just don't understand enough about fire behavior.

 

[Sifu]

I'm triggered.

712 speaks to each vertical opening.
712.1.6 speaks specifically to ducts and transfer openings and sends us to 717.
717.6 speaks to penetrations by ducts and air transfer openings and then
717.6.2 speaks specifically to membrane penetrations by the ducts and air transfer openings, but only to ceiling membranes.

714 speaks to through and membrane penetrations.
714.1.1 speaks specifically to ducts and transfer openings and sends us to 714.5 through 714.6.2.
714.5 speaks to penetrations of a fire resistance rated floor assembly OR the ceiling membrane of a roof ceiling assembly and sends us to 714.5.1 through 714.5.4.
714.5.2 speaks to membrane penetrations that are part of a horizontal assembly and sends us back to 714.5.1.1 or 714.5.1.2 with multiple exceptions that apply only the ceiling membrane.
714.5.1.1 tells us to follow the assembly as if the membrane penetration were a through penetration or
714.5.1.2 tells us to treat the membrane penetration as a through penetration which I guess means find a membrane penetration system for the floor membrane...which I can't find.

The only specific requirement for protection of any membrane penetration or opening in a rated horizontal assembly applies to the ceiling side of the assembly.

If I assume, based on the commentary that "openings" only occur between stories, then I have to throw out the references in 712 to 717. I am left with using 714 for protection of the assembly itself. 714 tells me to pretend the membrane penetration is a through penetration but I can't find a floor assembly or a membrane system that addresses the floor side opening/penetration.

When I write this out I want to apply for another career.

 

[steveray]

I am going to say that every through penetration addresses the top side....But I do share some of your pain...

 

[mtlogcabin]

I am trying to reconcile the listed assembly that includes flooring with the belief that any of the elements could be eliminated unless shown as optional.

The gypcrete requirement on the floor of the UL system is where the majority of the Sound Transmission Rating (STR) is achieved not the fire rating where the damper would be required.

 

[Penguin87]

Per UL testing standards, ALL ceiling assemblies are tested from the underside, only. It makes no sense to fire rate from above going down.

Taken from page 8 of the Gypsum Associatoin's 2009 Fire Resistance Design Manual Sound Control Gypsum Systems:

Where unsymmetrical systems were tested from one
side only, the side exposed to the test fire is indicated
by the words "Fire Side" on the system detail. When
documentation is available to show that the wall was
tested with the least fire-resistive side exposed to the
test fire, the wall need not be subjected to tests from the
opposite side and a "Fire Side" is not specified. All floor-
ceiling and roof-ceiling systems were tested with fire
exposure on the ceiling side.

From the 2021 IBC:

722.6.2.4 Floors and Roofs

In the case of a floor or roof, the standard test provides only for testing for fire
exposure from below. Except as noted in Section 703.2.3, floor or roof
assemblies of wood framing shall have an upper membrane consisting of a
subfloor and finished floor conforming to Table 722.6.2(4) or any other
membrane that has a contribution to fire resistance of not less than 15 minutes
in Table 722.6.2(1).

And the same concept is repeated in

The testing regime meets two objectives:

1) protect people on a floor above a fire, who may be unaware that a fire is occurring and need to be protected from the flame, as well as to prevent the floor structure from collapsing.

2) contain the fire in a corridor from spreading

 

[Yankee Chronicler]

It has been discussed on the forum before in other threads with the same conclusions. I don't know the exact system they are using but the questioner said that it was not designated as that was my first thought. As RLGA has previously educated me, ASTM E 119 says the systems are tested from the bottom side. I am trying to reconcile the listed assembly that includes flooring with the belief that any of the elements could be eliminated unless shown as optional.

BXUV very clearly says the ratings apply to the assemblies in their entirety. ASTM E 119/UL 263 clearly says they aren't tested from the top. So even if the test method does not include exposure from the top, do I get to just eliminate a portion of the system when it is part of the tested assembly? This is my dilemma (really his dilemma but I try to take advantage of any educational opportunity I can find).

Simple answer: No, you don't. It's not a rated "ceiling," it's a rated floor-ceiling assembly. Anything that goes all the way through the assembly requires a through penetration seal. Anything that goes through either face of the assembly requires a membrane penetration seal.

In jurisdictions that allow the local building official to grant modifications (my state does not), the local building official could grant a modification to omit floor dampers. Whether or not you might want to do that comes down to how risk averse you are. Personally, I would be very reluctant to grant such a modification unless the design offers something in exchange, to provide equivalent safety. The criterion our State Building Inspector uses when evaluating requests for modifications is whether equivalent safety is provided. When I was working for one of the better-known code consultants in the state, we always provided something beyond code minimums when we asked to omit something.

 

[klarenbeek]

If you look in the I-code sections (either IBC 717 or IMC 607) for duct and transfer openings, damper requirements are addressed for both through penetrations and for membrane penetrations. Since this doesn't go through both the floor and ceiling membranes its not a through penetration, the section covering through penetrations does not apply.
The section for membrane penetrations specifically calls out protecting duct and air transfer openings in the ceiling membrane. No mention is made of requiring a damper at a floor only penetration.

717.6 (607.6 IMC) Through penetrations.​

Penetrations by ducts and air transfer openings of a floor, floor/ceiling assembly or the ceiling membrane of a roof/ceiling assembly shall be protected by a shaft enclosure that complies with Section 713 or shall comply with Sections 717.6.1 through 717.6.3.

717.6.2 (607.6.2 IMC) Membrane penetrations.​

Ducts and air transfer openings constructed of approved materials in accordance with the International Mechanical Code that penetrate the ceiling membrane of a fire-resistance-rated floor/ceiling or roof/ceiling assembly shall be protected with one of the following:

I'm not seeing anywhere where dampers are required at floor only duct penetrations. Also, as far as I know there are no dampers listed for that application. By not installing the damper per its listing, you are voiding the listing of the damper. There are no one damper fits all applications out there. they are very specific to how they are installed in what kind of assembly.
In my opinion, if you are requiring dampers at floor only penetrations of a rated floor/ceiling assembly, you are requiring something the code does not require. Going to other sections that are not intended for duct openings, you are grasping at straws trying to justify something that's not required by code, plus shoehorning a listed damper into an application its not intended for.

 

[steveray]

717.1.2​

Ducts that penetrate fire-resistance-rated walls and are not required by this section to have fire dampers shall comply with the requirements of Sections 714.3 through 714.4.3. Ducts that penetrate horizontal assemblies not required to be contained within a shaft and not required by this section to have fire dampers shall comply with the requirements of Sections 714.5 through 714.6.2.

 

[klarenbeek]

So how are you protecting the penetration?

I think its covered here:

714.6.1​

Noncombustible penetrating items that connect not more than five stories are permitted, provided that the annular space is filled to resist the free passage of flame and the products of combustion with an approved noncombustible material or with a fill, void or cavity material that is tested and classified for use in through-penetration firestop systems.
INSIGHTS (1)

714.6.2​

Penetrating items that connect not more than two stories are permitted, provided that the annular space is filled with an approved material to resist the free passage of flame and the products of combustion.

 

[Sifu]

The last two posts from klarenbeek and steveray are the crux of my dilemma, beyond the "tested from below" fact. Lots of information for protecting the ceiling membrane, none for the floor membrane, yet 714 points us to the need to protect any membrane. Without seeing the MFR instructions for every possible damper installed in a floor (if there are any) I can't say there isn't one. One of my comments to the questioner was how a damper would work when a toy gets dropped into the floor register, or when it gets crushed by furniture rolling over it.

I went through the code paths for openings and it sends us to 717, which is all about ceiling membranes. I went through the code path for penetrations to get to membrane penetrations and it just says protect them as if they were through penetrations. I don't know how to do that other than a listed damper, if there is one, but I have checked about 10 from various MFR's and I don't see any that are for floors. All have been either ceiling radiation dampers, or listed for installation in walls.

I don't think the intent is for floor dampers, but what I think is less relevant than what I can prove. Evidence and critical thinking tell me my thinking is on target, but 714 puts a damper on what I think. (Pun intended).

 

[steveray]

What is the floor assembly?

 

[klarenbeek]

As long as there are no gaps between the duct and the floor, or they are covered by the register flange or a trim angle you meet 714. 6.1 and 714.6.2. At least thats how i read those sections.

 

[steveray]

I would find a floor through penetration and then allow whatever they allow at the top..In this case the weirdness is the top seems to require more than the bottom....

 

[steveray]

For L500 floors...Give UL a lil plug...

 

[klarenbeek]

Why doesn't 714.6.1 or 2 apply? I think we're over thinking this. Duct is metal and therefore non-combustible. These are among the sections 717 send you to.

 

[steveray]

Why doesn't 714.6.1 or 2 apply? I think we're over thinking this. Duct is metal and therefore non-combustible. These are among the sections 717 send you to.

Because 714.6 is for non-rated assemblies....And this floor is rated....

 

[Sifu]

Using 1/2 the system seems reasonable, yet suspect in that the listings are only valid if installed completely. Still, it is an elegant solution and one similar to the one I was thinking which is the one Klarenbeek points out, basically treating it as a non-rated penetration, which makes some sense since the 1/2 of the assembly we are penetrating doesn't seem to contribute to the rating. So we are dealing with 1/2 a rated assembly, using 1/2 a rated FS system. Do 2 halves seal a hole? (2 creative plays on words in a single day...Mic drop, I'm out!)

 

[klarenbeek]

Because 714.6 is for non-rated assemblies....And this floor is rated....

You are right. I'm more familiar with the ins and outs of the IMC/IFGC than the IBC plus I was commenting while also dealing with other things. I typically defer to/ask the building inspectors when it comes to the IBC. This is starting a discussion in our office, We had been ruling this based on the interpretations of our last two CBO's

 

[steveray]

Using 1/2 the system seems reasonable, yet suspect in that the listings are only valid if installed completely. Still, it is an elegant solution and one similar to the one I was thinking which is the one Klarenbeek points out, basically treating it as a non-rated penetration, which makes some sense since the 1/2 of the assembly we are penetrating doesn't seem to contribute to the rating. So we are dealing with 1/2 a rated assembly, using 1/2 a rated FS system. Do 2 halves seal a hole? (2 creative plays on words in a single day...Mic drop, I'm out!)

Similar to if they remove one half of what is now required to be a rated wall (old plaster on a tenant separation)...The half they put back has to comply without making the whole wall comply....