Horizontal assembly Fire rating-Multifamily

[TRIPTI.RAMPURIA]

I need to provide the UL assembly details for a building that has retail on the first floor and residential units on the two floors above. The construction type is VA. I’ve referenced UL Assembly L521 — is this the correct one for this condition? Also, would the same assembly apply for the ceiling of the second floor as well?

 

[Yikes]

Welcome to the forum! Where is the project located - - or more specifically, what is the applicable code?

 

[TRIPTI.RAMPURIA]

Welcome to the forum! Where is the project located - - or more specifically, what is the applicable code?

Its located in Kaufman , Tx. The city follows IBC 2015.

 

[Yikes]

There are several factors at play:
Table 601 for type VA requires one-hour floor construction, just to keep the building standing.

Table 508.4 requires an occupancy separation between R-2 dwellings and M mercantile of 1 hour for sprinklered buildings, or 2 hours for nonsprinklered buildings. You first need to choose whether you will sprinkler before you know how many hours for for the fire rating

Once you've determined the fire rating, then you need to select based on your preferred construction materials and systems. VA construction can be almost any material, though most people choose it because they want to use wood. Assuming you like the gang nail truss system and are intending to sprinkler the building (and the truss space), the UL L521 assembly will work for fire rating.

For sound transmission control, 2015 Texas IHB code 1207.2 requires an STC of 50+ and 1207.3 requires an IIC of 50+. In the UL catalog for L521, there are only 3 approved floor systems that were tested for fire, and UL did not test for sound. You'll need to find someone who has tested this assembly for sound.

My suggestion is to check out the Gypsum Association Catalog, which lists the fire ratings, STC and IIC sound ratings for each assembly. IHB Table 721.1(3) footnote (q) states:
"Generic fire-resistance ratings (those not designated as PROPRIETARY* in the listing) in the GA 600 shall be accepted as if herein listed."

 

[walker.t]

Table 508.4 requires an occupancy separation

But only they are are using separated occupancies.

You first need to choose whether you will sprinkler

I think the building will need to be sprinklered per 903.2.8.

My suggestion is to check out the Gypsum Association Catalog

Good suggestion, GA > UL.

would the same assembly apply for the ceiling of the second floor as well?

Confirm with the tested assembly you select. For example, looking down the table of contents in the Gypsum Association manual they have a section for floor-ceiling systems and roof-ceiling systems.

 

[Yikes]

But only they are are using separated occupancies.

Right. The original question is contingent on so many design factors that the only valid succinct answer can sound trite: "consult a registered design professional". But I don't know the O.P., and I do want to give them a starting point for further research.

BTW, I previously used plate-connected lumber floor trusses in multifamily housing projects. I moved away from them after I saw a fire test where it showed the metal plates popping off in the heat, causing catastrophic cascading failure. But they are still code compliant for their tested rating, and I still use them at roofs all the time. They're just not my first preference for long-span floor loads. I'd go with an open-web bar truss instead:

 

[TRIPTI.RAMPURIA]

I need to provide the UL assembly details for a building that has retail on the first floor and residential units on the two floors above. The construction type is VA. I’ve referenced UL Assembly L521 — is this the correct one for this condition? Also, would the same assembly apply for the ceiling of the second floor as well?

But only they are are using separated occupancies.


I think the building will need to be sprinklered per 903.2.8.


Good suggestion, GA > UL.


Confirm with the tested assembly you select. For example, looking down the table of contents in the Gypsum Association manual they have a section for floor-ceiling systems and roof-ceiling systems.

Right. The original question is contingent on so many design factors that the only valid succinct answer can sound trite: "consult a registered design professional". But I don't know the O.P., and I do want to give them a starting point for further research.

BTW, I previously used plate-connected lumber floor trusses in multifamily housing projects. I moved away from them after I saw a fire test where it showed the metal plates popping off in the heat, causing catastrophic cascading failure. But they are still code compliant for their tested rating, and I still use them at roofs all the time. They're just not my first preference for long-span floor loads. I'd go with an open-web bar truss instead:
View attachment 16899

Yes,
We have open web trusses.
The main question where we are stuck is whether we need 1hr rating or 2hr rating.
Although the space is protected by NFPA 13 Sprinkler system

 

[walker.t]

whether we need 1hr rating or 2hr rating

Based on what you’ve told us it sounds like you need only a 1-hour rating.

1. 1-hour rating per 420.3 Horizontal Assemblies (floor separation between dwelling and sleeping units and other occupancies.)
2. 1-hour rating for floor construction in Type VA per Table 601.
3. If your building is using separated occupancies, then as noted in #4, you only need 1-hour because your building is sprinklered.

I can’t think of anything else what would apply to require a 2-hour rating. Was there something that made you think it might need a 2-hour rating?

 

[TRIPTI.RAMPURIA]

Based on what you’ve told us it sounds like you need only a 1-hour rating.

1. 1-hour rating per 420.3 Horizontal Assemblies (floor separation between dwelling and sleeping units and other occupancies.)
2. 1-hour rating for floor construction in Type VA per Table 601.
3. If your building is using separated occupancies, then as noted in #4, you only need 1-hour because your building is sprinklered.

I can’t think of anything else what would apply to require a 2-hour rating. Was there something that made you think it might need a 2-hour rating?

The General contractor said that mostly they did 2hr in these kind of building. So we got confused.