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Drywall requirements for interior shearwalls, under TJIs etc.

Bernard Lam | Posted in Building Code Questions on

What are the requirements for using drywall as a flame break for:

1. Under TJI joists

2. Interior shearwalls (7/16″ sheathed 2×4 walls)?

3. Interior side of exterior shearwalls

4. Interior non structural walls.

In which of the above assemblies do I have to install drywall as a fire break? 

I ask this because I’d like to clad interior walls with wood strips/slats, as well as some Shou sugi ban fence boards, and I wonder if I need to install drywall first onto the studs/joists before the cladding material. 

The project is in boulder colorado if that makes a difference. 

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Replies

  1. Andy S | | #1

    Someone more familiar with the exact code sections can comment on that, but I'd be wary of cladding anything on an exterior wall without the drywall as an air barrier/control layer.
    Wood covered cathedral ceilings without drywall are well known moisture accumulators due to the leakiness of the cladding letting the warm moist air through to condense on the colder roof sheathing.

    1. Bernard Lam | | #3

      Andy - you are right, I do have drywall as the air control layer, as the ceiling directly below the roof trusses. That drywall I won't be disturbing. I'm cladding the ceilings below floor TJIs and interior structural and non structural walls.

  2. Jon A | | #2

    First off, you will need to look up the code requirements of your area as they vary across the country. I'm in MA so I'll answer your questions as they pertain to my state.

    Non- fire rated TJI floor joists require an approved method of fire protection. This is typically 1/2" gypsum but other materials and methods can be used including 5/8" wood structural panels, or rock wool between the joists. R302.13 from the 2015 IRC is the governing code section in my state. Also, the APA lists alternate methods to protect TJI's. See the link.

    https://www.apawood.org/i-joist-fire-assemblies

    Prescriptive braced wall panels (shear walls) will usually require 1/2" gypsum as an interior finish opposite the bracing material but there are some exceptions. See R602.10.4.3. - 2015 IRC. If you have a design professional designing an alternate shear wall, that design would supersede any prescriptive shear wall requirements so it would be up to that person to spec the interior material and fastening method.

    Hope this helps.

    1. Bernard Lam | | #4

      Thank you Jon, that's very helpful. Exactly what I was asking. Using rock wool is a great alternative, as it's easier to DIY install than lifting drywall into a ceiling. Though for sound maybe the drywall is still more effective. Regardless, now I know I do need to cover up the TJI s one way or another, thanks.

      For the interior shearwalls, I have an atypical situation where this wall is sitting directly in front of a concrete foundation wall on one side, and sheathed as a shearwall on the other. I wonder in this case if I'm required to add a layer of drywall infront of the structural sheathing in this case. I've looked upy local building code amendments and I don't see this mentioned anywhere, so I wonder what the IRC says about such an assembly.

      And it sounds like for general non structural interior walls I don't need drywall at all?

  3. Jon A | | #5

    "I have an atypical situation where this wall is sitting directly in front of a concrete foundation wall on one side, and sheathed as a shear wall on the other".

    Is this in a below grade area where the interior wall is non structural? You don't need a shear wall if you have a full height concrete foundation wall directly behind it. Who spec'd the interior shear walls?

    You don't need to use drywall for interior partitions.

    1. Bernard Lam | | #6

      That's what blows my mind. It's a daylight basement, interior full height foundation wall, perpendicular to the foundation wall retaining the hillside. I'd have expected the shear wall to start on top of the foundation wall but the engineer called out an interior shear wall spanning 2 levels from the slab and not the wall. Confused me for a while! I've attached the engineering plans for reference. Do you think I need drywall infront of the 7/16" sheathing for this wall?

      1. Jon A | | #7

        Are you referring to the interior shear wall by the stairs? I do see it is next to the foundation wall in the basement. Maybe its because the wall above is not directly over the foundation wall so you need to have the continuous wall below down to the slab? The notes for SW1 don't mention drywall at all so I would think you could plywood the accessible side of the basement wall per plan and than just drywall over it to finish. Just call the engineer to clarify.

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