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converting existing ceiling with 2x6 ceiling joist to one hr rated ceiling assembly

G

gelarehg@CotamDesign

GREENHORN
Joined
Apr 18, 2023
Messages
6
Location
Walnut Creek
Hi all,
I'm working on an ADU and came across a problem. there are existing 2x6 ceiling joists i and need to change them to a one hour fire rated ceiling assembly. Project is located in California. Some of the joists are 2x6 and some are 2x10, even though in the code it doesn't say the size of the joists and it just says 16 oc, but the plan checker asked to have 2x10 joists. I can sister up the 2x10 to the existing 2x6, and add more where I don't have them 16" oc. I reviewed chapter 7 On table 722.6.2 (1), adding Gyp Board Type "x" gives me 40 mins. On table 722.6.2(2) it says wood floor joists @16" oc gives me 15 mins. I'm still short by 5 mins. On table 722.6.2(5) it says "if the spaces between the studs are completely filled with glass fiber mineral wool batts weighing not less than 2 pounds per cubic foot (0.6 pound per square foot of wall surface) or rockwool or slag material wool batts weighing not less than 3.3 pounds per cubic foot (1 pound per square foot of wall surface), or cellulose insulation having a nominal density not less than 2.6 pounds per cubic foot."
I already have R-19 batt per energy calcs. Anybody can advice me how to make this change happen? can I use any of the insulation options in leu of R-19? Or any idea?
 
fatboy said:
Check the GA-600 Fire Resistance and Sound Control Design Manual. https://www.gypsumpublications.com/...re-resistance-and-sound-control-design-manual
Click to expand...
I did, can't find anything, I don't want to change the flooring on first floor, it'll be too expensive and also needs another permit. I just want to modify the ceiling on ADU side. have to add some material to give me more fire protection. I added resilient channel as well, but cant find the fire protection for it in the code
 
Try IBC Table 721.1(3)

FLOOR OR ROOF CONSTRUCTION
21. Wood joists, wood I-joists, floor trusses and flat or pitched roof trusses spaced a maximum 24" o.c. with 1/2" wood structural panels with exterior glue applied at right angles to top of joist or top chord of trusses with 8d nails. The wood structural panel thickness shall be not less than nominal 1/2" nor less than required by Chapter 23.​
ITEM NO.
21-1.1​
CEILING CONSTRUCTION
Base layer 5/8" Type X gypsum wallboard applied at right angles to joist or truss 24" o.c. with 11/4" Type S or Type W drywall screws 24" o.c. Face layer 5/8" Type X gypsum wallboard or veneer base applied at right angles to joist or truss through base layer with 17/8" Type S or Type W drywall screws 12" o.c. at joints and intermediate joist or truss. Face layer Type G drywall screws placed 2" back on either side of face layer end joints, 12" o.c.​
 
gelarehg@CotamDesign said:
Hi all,
I'm working on an ADU and came across a problem. there are existing 2x6 ceiling joists i and need to change them to a one hour fire rated ceiling assembly. Project is located in California. Some of the joists are 2x6 and some are 2x10, even though in the code it doesn't say the size of the joists and it just says 16 oc, but the plan checker asked to have 2x10 joists. I can sister up the 2x10 to the existing 2x6, and add more where I don't have them 16" oc. I reviewed chapter 7 On table 722.6.2 (1), adding Gyp Board Type "x" gives me 40 mins. On table 722.6.2(2) it says wood floor joists @16" oc gives me 15 mins. I'm still short by 5 mins. On table 722.6.2(5) it says "if the spaces between the studs are completely filled with glass fiber mineral wool batts weighing not less than 2 pounds per cubic foot (0.6 pound per square foot of wall surface) or rockwool or slag material wool batts weighing not less than 3.3 pounds per cubic foot (1 pound per square foot of wall surface), or cellulose insulation having a nominal density not less than 2.6 pounds per cubic foot."
I already have R-19 batt per energy calcs. Anybody can advice me how to make this change happen? can I use any of the insulation options in leu of R-19? Or any idea?
Click to expand...
Good morning,
To be clear, you may use the CBC or the CRC for an ADU. Many use the CRC because they do not want to pay for a licensed professional.
However, any separation from one unit to another must have a 1 hr. listed separation. You cannot piece together as you are stating. I would never accept anything short of a true 1 hr. listed assembly. Whomever said to check the Gypsum manual is right on track. They have UL approved designs that will give you what you need. You may have to incorporate new framing, but not by adding a 2 x 10 onto a 2 x 6 as the assembly is specific. I have not observed in that manual any sort of framing that does this. You may wish to verify with an architect if they have a method for any adjustment such as yours.
Best of Construction......
 
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