Fire Resistant Assemblies

Currently, there are only three sources included in the CBC (IBC 2009):  Gypsum Association's GA-600 (generic assemblies only), the prescriptive requirements in the CBC Chapter 7, and the calculated methods in CBC Chapter 7.


Other resources that could (and typically are) accepted by building officials are those listed in UL's Fire Resisitance Directory and within specific Evaluation Service Reports prepared by ICC-ES.


FM Global has a list of approved materials, but does not have a directory of tested assemblies, except for roofing.

This is in regards to a project (R-2, Type VB, fully sprinklered) designed under the 2010 CBC:  Section 712.3, Exception:  says that floor/ceiling assemblies between dwelling units are not less than ½ hour rated with sprinklers throughout.  


Also, Section 709.3 Exception 2: says that walls between dwelling units are not less than ½ hour with sprinklers throughout.  


Is there such a thing as 1/2 hour rated assemblies?

I think I have seen only one assembly and if I recall correctly it was in UL, but I'm not sure.


Since you're using wood construction, I suggest using the calculated method per CBC Section 722.6.  Wood studs at 16 inches o.c. have a 20-minute time (Table 722.6.2(2)) and 1/2-inch gypsum board has a 15-minute time (Table 722.6.2(1)).  Since you can only count the membrane on one side plus the framing per Section 722.6.2.1, this is considered a 35-minute assembly.


For floor/ceilings, the wood joists have a 10-minute time (Table 722.6.2(2)) and adding two layers of 1/2-inch gypsum board at the ceiling provides a 30-minute time (2 x 15 min. = 30 min.).


However, since the walls between the units are required to have an STC of 50, you will have to add (at least) sound attenuation insulation, the rating for the wall will increase because the insulation adds another 15 minutes per Table 722.6.2(5).  But, since the wall assembly has not been tested for a STC, a field test will likely be required to demonstrate that the installed assembly as a Field STC of 45 or greater.


My suggestion...keep it simple and use a tested 1-hour assembly that has a tested STC of 50 or greater.  I don't know why the IBC code development process accepted the 1/2-hour assembly provisions.

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