Hi all. I am finally getting my workshop started. It’s going to be slab on grade, 2 story with apartment above. California if it matters. The engineer has specified most of the walls to be shear walls and two exterior walls need to be 1hr fire rated. I thought I had that all figured out, but am running into a few head scratchers that I havent been able to find information on.
The first floor is 10 ft ceilings (2× sill, 116 5/8 studs, then a double 2x top/cap plate) and second floor is 9ft ceilings. What placement of the osb would you recommend? If i run 10, osb vertically it is not going to reach from the top of the cap plate to the bottom of the sill plate. Details show the joint to be at the rim joist. So do I need to plan 9′ sheet and a smaller sheet either at top or bottom with blocking?
Also, when the framing is flush with the foundation, isn’t it a good practice to extend osb 1″ past the sill plate? Do I just rely on flashing instead?
Lastly, I was hoping to use zip system, but doesn’t seem like there is a fire-rated version. Is there a similar system that you would recommend that is fire-rated?
Appreciate the help. Long time follower and very happy to be at the point where I can finally ask my own questions. 🙂
Replies
Do not run your osb below the bottom plate. It accomplishes nothing and asks for moisture problems. 10’ plywood will give you adequate nailing top and bottom. 10’ plywood on top should cover the rim joist and the 9’ wall above. You are not required to cover the rim joists, but you will need straps from the upper to the lower shear panels at the corners and probably to the foundation. Your exterior finish should give you a 1 hour rating. Stucco will and I would assume fiber cement siding does. Where I live in California combustible material cannot be used on the exterior at all. This varies by fire zones. I assume your 1 hr walls are close to the property lines. There is exterior gypsum made for this use.
Okay that makes sense. Thank you. I was under the impression it was required to have a single panel (or properly blocked panels) run the full width sill to cap plate.
I may have missed it but what is type and depth of the floor system between the two floors?. If its less than 10” you should be able to stack two 10’ panels on top of each other without any smaller panels.
The structural engineer should have made notes on the plans for what hardware goes where as well as specced out a fastener schedule for all sheathing. Generally, you would install 2x or 4x blocking at any sheathing edges that don’t land on studs, plates or rims.
Google “one hour fire walls” to see some options. It needs to be a tested and approved design. Hardie siding won’t cut it. One we see is 5/8 exterior rated fire rock sheathing applied to the exterior of wall studs and another layer of 5/8” rock on the interior. The 5/8” exterior rock will usually extend behind the soffit and fascia and be firetaped as well. Find out before you frame what tge inspector wants to see. I would expect in California all of this info would be required on the plans to be submitted for permits?
We will likely be using 2x12 floor joists, so I will likely need to have a small strip between top and bottom panels.
For the fire-rated walls we were going to use UL Design No. V340 in an attempt to avoid drywall on exterior. https://lpcorp.com/blog/specifying-1-hour-fire-rated-walls