# acheiving fire rating in wood stud/gypsum board drop ceiling



## sal (Jul 17, 2017)

This is for a 1 hour stc 50 requirement in a ceiling floor assembly. I have an existing building and a wood stud drop ceiling. Was going to specify 2 layers of type "x" over rc-1 Chanel at the drop ceiling, then roxul between the 2x6 studs at the floor structure above. Is this a good solution?

I can't find a similar ul for this type of assembly but figure 40+40 min for 2 layers of type x will cover me for over an hour. I think just 1 layer would have sufficed bu read in the gypsum association manual that if you said insulation to add another layer of type X.


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## TheCommish (Jul 17, 2017)

if you need a true rating, look to the  gyp board manufactures for a complete assembly meathod. UL among others lists  spicific construction to achive the desired rating.  you can not just add another layer  to somthing.


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## sal (Jul 17, 2017)

i cannot find anything for a similar drop ceiling in the manual.   Should a 'true" ceiling be installed in the upper ceiling in this case? The drop ceiling below just cosmetic?


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## pyrguy (Jul 17, 2017)

Remember that gyp ratings are for use in wall construction. Ceilings are different.


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## steveray (Jul 18, 2017)

sal said:


> i cannot find anything for a similar drop ceiling in the manual.   Should a 'true" ceiling be installed in the upper ceiling in this case? The drop ceiling below just cosmetic?



That would be best/ easiest...otherwise you have to rate all of the penetrations of the "dropped" ceiling (light fixtures, HVAC registers, etc...)


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## ADAguy (Jul 18, 2017)

Sal, how old is the building?


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## sal (Jul 18, 2017)

atleast 50-60 years,  its all balloon framed.

I would have liked to instal 2 layers of gyp at the drop ceiling,, but don't know if that created plenum space causes heat build-up.


If instaling rated 'real" ceiling above,  would the drop ceiling below be an issue for heat build-up?


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## sal (Jul 18, 2017)

TheCommish said:


> if you need a true rating, look to the  gyp board manufactures for a complete assembly meathod. UL among others lists  spicific construction to achive the desired rating.  you can not just add another layer  to somthing.




New construction requires a true 1 hour rating, but this is an existing building.   Does this make it the inspector's call?  

When using the calculated method, the code states type "x" gyp is 40 min. So why wouldn't 2 layers that suffice ( if we are not going for a tested assembly)
Does the calculated method specify for method of assembly? Where is this in the code?


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## TheCommish (Jul 18, 2017)

Maybe you should hire a registered design profesional to  do the design and stop trying to make things work


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## Paul Sweet (Jul 19, 2017)

Gypsum Association Fire Resistance Design Manual construction FC-5406 sounds similar to what you're describing.  The 2 layers of 5/8" type X provide 1-hour protection for the framing.

Firestopping at the dropped ceiling will be critical, as well as protection of penetrations..


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## ADAguy (Jul 19, 2017)

Roxul appears to be an interesting product not often seen south of you. I could not find any standard details on their website.
It is noncombustable and therefor fire resistant but can it be added to flammable material to protect it? If so, how much is required to do so?


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## pyrguy (Jul 20, 2017)

2012 IBC Table 722.2.1.4(2) that gives the calculated fire resistance ratings for GWB is for the fire exposed side of walls.


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## PJC89 (Jul 27, 2017)

I would ask that you look at Chapter 7 of the IBC for reference.  There are two sections that may be useful: prescriptive fire resistance rating (Section 721) and calculated fire resistance rating (section 722).

They have a list of assemblies that achieve a fire resistance rating based on different configurations and then they have a method for calculating the fire resistance rating if the assembly is not within Section 721. 

https://up.codes/viewer/general/int...pter/7/fire-and-smoke-protection-features#721


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## cda (Jul 27, 2017)

Welcome PJ

You give some very lucid answers 

So how long have you been dealing with codes???


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