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Horizontal Seperation - Assembly shall be continuous - interpretations?

Darren Emery

Darren Emery

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Oct 20, 2009
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Location
Manhattan, Ks
2009 IBC

420.3 requires a horizontal floor assembly between dwelling units in R2 - constructed per 712

712.4 states assembly shall be continuous

Question - given a 3 story 24 unit apartment building - do you see this as requiring a continuous seperation within each dwelling unit, or continuous from outside wall to outside wall of entire floor.
 
Within each dwelling unit. Areas of the floor/ceiling assembly that are not providing dwelling separation would not require the rating, unless needed to satisfy another section of the code.
 
My interpretation is that it is continuous to the nearest supporting structure having an equal or greater fire-resistance rating.

For example let's assume a building's structural framing uses a bay system of 20'x30' with columns at the corners and girders/beams spanning between the columns. If only one portion of one bay is required to have a fire resistance rating, then the entire bay, including the columns and girders/beams supporting that bay, will need to have the required fire-resistance rating.

If the fire-resistance-rated floor/ceiling assembly has a plenum space that would be open to unprotected bays, then the plenum will need to be sealed off with construction of equal or greater fire-resistance and any penetrations must be equally protected.
 
In this specific case, exception 2 to 712.4 wouldn't require the supporting construction to be rated. Between 420.2 and 420.3, the code is simply trying to compartmentalize each dwelling/sleeping unit (IMHO).

In practice, it may be easier to provide a single rated assembly detail for the entire floor, required or not.
 
permitguy said:
In this specific case, exception 2 to 712.4 wouldn't require the supporting construction to be rated. Between 420.2 and 420.3, the code is simply trying to compartmentalize each dwelling/sleeping unit (IMHO).In practice, it may be easier to provide a single rated assembly detail for the entire floor, required or not.
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Still on 2003...don't have those exceptions...as a bit of an aside...how do you maintain the horizontal rating when it is interrupted by an unrated bearing wall?
 
RLGA said:
My interpretation is that it is continuous to the nearest supporting structure having an equal or greater fire-resistance rating.
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Your interpretation is inconsistent with the code section cited which requires separation of dwellings. This doesn't mean that the separation won't have to extend beyond the dwelling boundaries so that supporting members are protected - but it does not mean that it must extend beyond the dwelling boundaries either.

In other words, determination of what requires protection must be project specific rather than pre-determined.
 
Still on 2003...don't have those exceptions...as a bit of an aside...how do you maintain the horizontal rating when it is interrupted by an unrated bearing wall?
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420.2 requires the walls to be rated as well (fire partitions), so the dwelling gets complete separation.

The '03 (Ch. 7) and '06 (Ch. 4) had similar requirements, but didn't specifically list the exception for the supporting construction. I'm not sure the intent was different, but the letter of the code would have specified and installation closer to what RLGA suggested above. In any case, the building official could allow an alternative method in accordance with the more recently published code, even if not formally adopted.
 
Ok...let's step away from the somewhat poorly written code language for a moment, and talk practicalites. Does it seem odd to anyone else that I can have one wire penetrate the top plate of my apartment's interior closet wall, and that has to be firestopped. But one foot away, at the top plate of the common wall between my apartment and my neighbor's apartment, there are 4 PVC drain stacks penetrating the top plate, and that just has to be fireblocked.

And to top it off - the plumber used fireblock foam. That stuff does burn, ya know.
 
Assuming that the drain stacks were included in the testing of the assembly, and the wire was not, that would be a proper installation in accordance with the code. The inspector must have been a real stickler!
 
permitguy said:
Assuming that the drain stacks were included in the testing of the assembly, and the wire was not, that would be a proper installation in accordance with the code. The inspector must have been a real stickler!
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No testing or assembly issues in the common wall - the horizontal assembly stops at the dwelling unit wall. Therefore the space within the common wall only requires a fireblock - no firestop - no through penetration firstop system - just good ole fireblocking....

It seems code compliant, but not common sense compliant to me.
 
The wall between units is typically a single tested assembly - there's nothing unusual about having services in a rated wall.
 
brudgers said:
The wall between units is typically a single tested assembly - there's nothing unusual about having services in a rated wall.
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Agreed - nothing unusual at all. What is unusual to me is the lack of requirement for firestoping through penetrants at the top plate in that wall. THAT seems odd to me.
 
In 101 land.....where a vertical assembly penetrates a "required rated" horizontal assembly; the penetration must have the rating permitted for the penetrated assembly. Just another comment :)
 
A penetration in the top plate of the wall is neither a through-penetration nor a membrane-penetration. Many of the designs in the UL directory call for top/bottom plates to be "firestopped," but they don't specify a prescriptive method or specify a listed firestop system. As for materials incorporated into the building element, the following would apply:

703.2 Fire-resistance ratings. The fire-resistance rating of building elements, components or assemblies shall be determined in accordance with the test procedures set forth in ASTM E 119 or UL 263 or in accordance with Section 703.3. Where materials, systems or devices that have not been tested as part of a fire-resistance-rated assembly are incorporated into the building element, component or assembly, sufficient data shall be made available to the building official to show that the required fire-resistance rating is not reduced. Materials and methods of construction used to protect joints and penetrations in fire-resistance-rated building elements, components or assemblies shall not reduce the required fire-resistance rating.

Exception: In determining the fire-resistance rating of exterior bearing walls, compliance with the ASTM E 119 or UL 263 criteria for unexposed surface temperature rise and ignition of cotton waste due to passage of flame or gases is required only for a period of time corresponding to the required fire-resistance rating of an exterior nonbearing wall with the same fire separation distance, and in a building of the same group. When the fire-resistance rating determined in accordance with this exception exceeds the fire-resistance rating determined in accordance with ASTM E 119 or UL 263, the fire exposure time period, water pressure and application duration criteria for the hose stream test of ASTM E 119 or UL 263 shall be based upon the fire-resistance rating determined in accordance with this exception.

Whether the building official required such documentation in your case, I have no idea. In reality, many don't consider it a substantial problem, and some even adopt policies on what they will or will not accept before requiring more documentation. There may be nothing to the fact that the wire is firestopped and the pipes are not. It could simply be the difference in training between the plumber and electrician, and it isn't like the inspector is going to tell the electrician not to exceed the code.
 
PG,

I think what Darren is saying is that the double top plate is the penetration(of the horizontal rated assembly) (and is not rated)...and then it is being penetrated again....
 
Good discussion with a point made where the non-rated interior walls have penetrations at the sole or single top plate within the sleeping or dwelling unit. Even with a double top plate the it's not permitted to penetrate the plates through the ceiling membrane unless AHJ invites differently. It appears the 2012 IBC will make this statement, but offers no exceptions that not already there in the code.

"The second and third changes both occur in the IBC. The first IBC change adds language that permits the ceiling membrane of a one- or two-hour floor-ceiling system to be interrupted by the “double wood top plate” of a partition as long as the fire-resistance rating of the wall system is not lower than the rating of the horizontal floor- or roof-ceiling system. The proposal was submitted by a group of code officials from Colorado and, after some massaging, received broad support from a variety of organizations.

The code modification addresses the problem that an applicator can encounter when installing a fire-rated partition to the underside of a gypsum-membrane fire-rated horizontal system. Construction sequencing operations often make it difficult to install the sheet or sheets of board to the underside of the floor system that provide a continuous membrane immediately above the point where the partition and the floor system intersect. During testimony code officials also noted concerns about the drywall membrane being crushed as the horizontal system moves and settles after building occupancy.

The approved language resolves the situation by allowing the double wood top plate to function as a substitute for the membrane and by acknowledging the fire-resistive contribution of the layers of board on the intersecting partition. It is notable that the approved language is not applicable to non-rated partition intersections and, because it is triggered by the requirement for a double wood top plate, it does not apply to traditional metal stud partitions."

Source: http://www.wconline.com/Articles/Column/BNP_GUID_9-5-2006_A_10000000000000874339

 
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