# Fire Rating Question



## Philarchitect (Dec 24, 2021)

Hello,
Our office is constructing an addition above an existing 7-story structure. The existing structure was originally constructed out of module steel boxes with light gauge cold-rolled steel floor, ceiling & wall infill framing. The new floor will be posted up above the existing roof framing. The final assembly will be a combination of new floor & old roof framing.
My question pertains to the proper fire-rated assembly. I have created a detail which should make this a bit more clear. Use the link below to access the detail. Hopefully someone can give me some advice. 









						Floor Assembly - Composite Condition.pdf
					

PDF File



					1drv.ms


----------



## Philarchitect (Dec 24, 2021)

Philarchitect said:


> Hello,
> Our office is constructing an addition above an existing 7-story structure. The existing structure was originally constructed out of module steel boxes with light gauge cold-rolled steel floor, ceiling & wall infill framing. The new floor will be posted up above the existing roof framing. The final assembly will be a combination of new floor & old roof framing.
> My question pertains to the proper fire-rated assembly. I have created a detail which should make this a bit more clear. Use the link below to access the detail. Hopefully someone can give me some advice.
> 
> ...


Update: I forgot to mention that I am looking for a 1-hour fire rating


----------



## Paul Sweet (Dec 24, 2021)

How are the existing floors fire protected? 

Gypsum Association FC-4490 provides 1-hour fire rating.  The double layer of 5/8" type X gypsum board provides 1 hour protection for the framing.


----------



## Builder Bob (Dec 24, 2021)

You may want to look at calculated fire resistance as I don't know that an UL listing exists for the type of construction depicted.


----------



## Philarchitect (Jan 4, 2022)

Paul Sweet said:


> How are the existing floors fire protected?
> 
> Gypsum Association FC-4490 provides 1-hour fire rating.  The double layer of 5/8" type X gypsum board provides 1 hour protection for the framing.


Thank, but unfortunately that assembly contains a plywood subfloor which would not be permitted in the Type-II, non-combustible construction.


----------



## steveray (Jan 4, 2022)

Like BB said...I think calculated should get you there.....


----------

