A fire-resistance rating of ½ hour when residence is equipped with fire-sprinklers.

[Linder]

The 2022 residential fire-resistance code R302.3 Two-Family Dwelling, Exception 1 states A fire-resistance rating of ½ hour shall be permitted in buildings equipped throughout with an automatic sprinkler system install in accordance with section R313.
Does this mean that 1/2-inch drywall on separation walls, bearing walls and ceilings will meet this requirement?

 

[classicT]

Considering Los Gatos and use of "2022", I presume that you are referencing the 2022 California Residential Code, which is based upon the 2021 IRC.

The residential code does not include fire resistance-rated assemblies nor a method to do calculated fire resistance. As such, the pathway is through the commercial building code. Under the 2022 CA-BC (2021 IBC), see Section 722 - Calculated Fire Resistance.

Per Table 722.6.2(1), the time assigned to a 1/2-in GWB is 15-minutes. 5/8-in Type X will get you 30-min., 1/2-in Type X 25-min., 19/32-in WSP (exterior glue) 15-min., etc.

Then, per Table 722.6.2(2), the time assigned for contribution of wood framing is 20-min for wood studs at 16-in o.c.

So, it is possible to achieve a 30-min rating with 1/2-in GWB over woods studs 16-in o.c.

 

[Linder]

Hello classicT:
Yes, I am referring to California building code.
Thank you for your response and guiding me to Section 722. Very helpful.
A 2nd floor will be added to a single-family residence and under a portion of 2nd floor will be converted to an Accessory Dwelling Unit (ADU).
The floor structure for the 2nd floor will be 16-inch tall open-web trusses at 16-inch OC spanning 21.5-feet. The trusses will be spaced above the 1st floor top plate with 4x8 lumber. The existing 2x6 ceiling joist will remain in place with about a 2-inch separation between top of (E) CJ and bottom of Trusses.
I didn't see anywhere in Section 722 that assigns a time to the trusses. There is time assigned for the contribution of the CJ.
Maybe it would be best to have 5/8-inch GWB installed over the (E) 1/2-inch ceiling GWB. Your thoughts?

 

[classicT]

Ahh, you are looking at a floor-ceiling assembly then.

Table 722.6.2(2) will provide 10-min for wood floor and roof joists 16-in o.c.. But given that you have trusses, that is of no direct use.

Given the use of trusses, you will instead need to use a prescriptive or tested assembly. Prescriptive assemblies can be found in Table 721.1(3); take a look at item number 21-1.1 below. Or, if you would like to go with a listed assembly, use the UL Product iQ or GA 600 Design Manual.

FYI - Note that the IBC does not have 30-min prescriptive assemblies.

 

[Linder]

You answered my question about walls in your 1st response, thank you.
I did see Table 731.1(3) but it seems to not include open web trusses. I was thinking I needed to find a listed assemble. I previously found an open web truss 1-hour assembly below, but it also includes an STC rating which I don't think this project will require. I could not find a 1/2-hour assembly. Maybe such an assembly doesn't exist. It might be time for me to have a discussion with the building official.
Thank you for your responses. 

 

[TheCommish]

Check to see if the bearing wall now need to have a rating as they are supporting the rated ceiling floor above

 

[Linder]

Check to see if the bearing wall now need to have a rating as they are supporting the rated ceiling floor above

Thank you for your response. Yes, bearing walls need to have the same rating.

 

[Robert]

You answered my question about walls in your 1st response, thank you.
I did see Table 731.1(3) but it seems to not include open web trusses. I was thinking I needed to find a listed assemble. I previously found an open web truss 1-hour assembly below, but it also includes an STC rating which I don't think this project will require. I could not find a 1/2-hour assembly. Maybe such an assembly doesn't exist. It might be time for me to have a discussion with the building official.
Thank you for your responses. View attachment 11944View attachment 11946

Don't you need sound separation between dwelling units (as this listing shows)?