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1 hour party wall assembly, specifically U 305(GA WP5512)

R

Rikkiboy13

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Jun 1, 2023
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9
Location
Aurora, Colorado
I have an inspector telling me that you are required to have Gyp-Crete in the 1" gap between plates within the wall cavities. I've been a structural inspector for more than 15 years and never heard of this. Can't find it in the UL tested assembly and would like some feedback on this?
 
The inspector is incorrect. The the gypsum underlayment has nothing to do with the fire-resistance performance of the wall assembly. If the floor (i.e, horizontal assembly) requires the underlayment as a part of the rated floor assembly (which I seriously doubt is the case), then the gypsum underlayment would need to be continuous under the sole plates of the framed walls.
 
RLGA said:
The inspector is incorrect. The the gypsum underlayment has nothing to do with the fire-resistance performance of the wall assembly. If the floor (i.e, horizontal assembly) requires the underlayment as a part of the rated floor assembly (which I seriously doubt is the case), then the gypsum underlayment would need to be continuous under the sole plates of the framed walls.
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I agree with you. He does not understand the ratings and how they work. These are apartments and the rating even show the Gyp-Crete butting up to the drywall of the party wall. The rating is within the unit not within the Party wall cavity. Do you know where I can get some information to prove this point? UL no longer offers any clarifications on their fire assemblies.
 
If I understand correctly, they are not questioning the wall assembly, but rather the floor assembly. What UL assembly are you using for the floor assembly?
 
RLGA said:
If I understand correctly, they are not questioning the wall assembly, but rather the floor assembly. What UL assembly are you using for the floor assembly?
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He's trying to use a Floor/Ceiling rated assembly within the Party wall assembly. He tells me that the entire floor/ceiling assembly is the entire floor of the building and the wall assembly is in addition to the floor assembly.
 
Based upon the listing, the gypcrete is only provided for the STC rating. With Flooring System No. 1, there is no gypcrete even used. Total of 8 different Flooring System options are provided. If you have a UL Product iQ profile, see BXLUV.L521.

Inspector is incorrect. May need to provide a polite call to the BO if the inspector does not rethink his stance after reviewing the listing.
 
classicT said:
Based upon the listing, the gypcrete is only provided for the STC rating. With Flooring System No. 1, there is no gypcrete even used. Total of 8 different Flooring System options are provided. If you have a UL Product iQ profile, see BXLUV.L521.

Inspector is incorrect. May need to provide a polite call to the BO if the inspector does not rethink his stance after reviewing the listing.
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Yes but System 1 has a "double thick" subfloor/ finished floor.....So I wouldn't say that the gyp isn't part of the rating unless you are seeing something else....

Shirley there are other things the inspector could fail it for if only they read the listing....
 
steveray said:
Yes but System 1 has a "double thick" subfloor/ finished floor.....So I wouldn't say that the gyp isn't part of the rating unless you are seeing something else....

Shirley there are other things the inspector could fail it for if only they read the listing....
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Correct me if I'm wrong but there is no floor/ceiling rating required within a rated wall assembly. Look at the detail I provided and it clearly shows the floor/ceiling butting up to the rated wall assembly. I wish Rich Walker was still at UL to provide some information.
 
steveray said:
Yes but System 1 has a "double thick" subfloor/ finished floor.....So I wouldn't say that the gyp isn't part of the rating unless you are seeing something else....

Shirley there are other things the inspector could fail it for if only they read the listing....
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Without knowing floor finish or additional information, we are all spit-balling. That said, I think it is plainly evident that the gypcrete is for the STC rating.
 
Rikkiboy13 said:
I'm not talking about the floor within the unit. It's the 1" gap between the double party wall.
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I'm aware... That's why it would be ridiculous for the inspector to worry about this. The gypcrete is for sound attenuation. Any sound resonating from the interior of the double wall is addressed by the walls, not by the floor assembly.
 
classicT said:
I'm aware... That's why it would be ridiculous for the inspector to worry about this. The gypcrete is for sound attenuation. Any sound resonating from the interior of the double wall is addressed by the walls, not by the floor assembly.
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Exactly, that's what is frustrating about why he thinks a floor/ceiling assembly would be required in this wall cavity.
 
The situation depends on the the required floor/ceiling fire-resistance rating and what is requiring the fire resistance rating.

If the construction type requires a 1-hour assembly (e.g., Type VA), the rating must be continuous under wall assemblies.

If the construction type does not require a fire-resistance rating (e.g., Type VB) but is only required for dwelling unit separation, the extent of the fire-resistance-rated floor need only extend between the dwelling unit separations (i.e., fire partitions and not “party walls”).

Per UL Design L521, System 2, the gypsum board is part of the rated assembly is not an optional material.
 
However, regardless of my response above, it can be argued that the fire-resistance of a floor/ceiling assembly is unidirectional and is predominately provided by the membrane at the underside of the joists. The subflooring and underlayment provide structural stability for the joists and the plates for the walls can provide that stability where the underlayment is not provided.

The fire-resistance rating for a wall assembly is bi-directional, and the wall membrane (e.g., gypsum board) on one side plus the framing provides the fire-resistance rating for fire exposure on that one side. Thus, it could be argued the the wall is providing the protection for anything within the cavity of the wall.

If the inspector is persistent, you could provide System 1 and install a strip of 15/32” plywood underlay Within the 1-inch gap.
 
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