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We have a 1951 open-framed garage attached to the house with 2x4 wall construction on 16" centers. The wall between the garage and living has 1/2" drywall on the inside wall, but nothing on the garage-side wall. We added an additional 2x4 framing layer for additional insulation space, so 7" thick total. (In the picture below the insulation is only in the first framing layer.)

There is an electrical panel in this wall, too.

The wall in question is 13'x8' plus a triangle section 13'-wide by 4'-tall at the apex centered at the 13' span (looks like a mailing envelope). Between the 8x13' section and the triangle section there is a top-plate. (The triangle part is not pictured.)

We are in Seismic Design Category D (or at least, the nearest city Portland Oregon specifies as such, we are in Washington county).

How can I accomplish the following?

  1. Secure the wall as a shear wall with structual-1 plywood and a nailing schedule for earthquake mitigation.
  2. Have removable panels on the studbay with the electrical panel for future wiring expansion. (perforated shear wall?)
  3. Meet fire separation code between the garage and house.

Item #2 is really the one that makes this interesting, its where I want to have my cake and eat it too.

Not sure if this should be a separate question:

  • Does the old and new framing layers need to be tied together somehow for the shear wall?

    • If sow, how?
  • What are my options?

Here is a picture from the garage-side:

Garage Wall for Seismic Retrofit]

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    What Seismic Design Category are you subject to? Do you need access from the house side, the garage side, or both? Which way does the electrical panel face, for that matter? Oct 7, 2021 at 1:45
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    How long and how tall is the wall between the garage and living?
    – Lee Sam
    Oct 7, 2021 at 4:38
  • I'm not conversant with the shear wall regulations for your locale (since we don't know it), but would having a cutout in the plywood the size of an electrical panel really violate the rules by degrading the strength of the wall? The removable plywood, maybe, but if that's the case, open every knockout and install conduit running up and/or down so you've got plenty of room to pull new wires through conduit, then you don't need a removable section.
    – FreeMan
    Oct 7, 2021 at 12:26
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    @ThreePhaseEel, Seismic Design Category D (or at least, the nearest city Portland specifies as such, we are in county).
    – KJ7LNW
    Oct 7, 2021 at 21:16
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    @Harper-ReinstateMonica, that's why we're asking this question now before circuits are run. The panel is inactive.
    – KJ7LNW
    Oct 7, 2021 at 21:47

1 Answer 1

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What I'd do to get you out of the corner you painted yourself into

Your original plan to flushmount the panel painted you into a bit of a corner as you'd have to rip out significant chunks of the wall sheathing whenever you wanted to rewire due to the fact that in SDC D2, you need 12.5' of intact shearwall sheathing at maximum (50') shearwall spacing. Instead, I'd bend the service conduit and adjust the panel location so that the panel can be surface-mounted to the wall atop the garage-side sheathing, 1" out from the plane of the studs, with some temporary 5/4 shims holding it in place until the wall can be sheathed. With that out of the way, you can then install the sheathing, although it'll take some tricky piece-jointery and fire-taping to work around the existing conduit when doing this. You'll need ⅜" structural panels (plywood or OSB) along with ⅝" Type X drywall atop the structural panels for this; the ⅜" thickness comes from IRC Table R602.10.4 for CS-WSP bracing, while the ⅝" Type X drywall is needed to match the test conditions for the rest of the parts we're using here.

Once that's done, you can then use some STI SpecSeal LCI (about $10 or so per tube from building supply houses or industrial MRO suppliers) to seal around the conduit penetration (max ⅞" annular space, minimum ⅝" bead depth, finished flush with the wall) in accordance with XHEZ.W-L-1527; this is permitted for an angled pipe by the following text from XHEZ.GuideInfo:

Where the uninsulated penetrating item in the individual design is indicated as a metallic pipe, conduit, tube, duct or cable, and the firestop system consists at minimum of a fill material (such as sealants, putty or mortar), the penetrant may pass through the opening in the wall or floor assembly at any angle, provided the annular space is maintained on both sides of the wall or floor assembly and all other specifications in the design are satisfied. In all other cases, except where otherwise indicated in the system, the penetrating item should penetrate the wall or floor assembly at a 90° angle.

Now that we have the wall sheathed and the service conduit penetration firestopped, we can then install an STI EZ-Path 22 (or two of them, one each side of the service conduit, if you need more room) mounted above the panel so that they discharge into the attic space over the dining room, with 5/8" Type X on the house side of the wall in this area. These devices provide UL tested and listed firestopping for as many or few NM cables (up to 8/3) as you can fit into them (visual 100% max fill), and can be re-entered at a later date without having to take anything apart, for around $100 a piece through the same suppliers that you can find the SpecSeal at.

Why all this work?

There is a more important reason than "shearwall sheathing replacement annoyance" that I'm doing it this way, though. As Square-D explains in data bulletin 0100DB0704, loadcenters are not intended to go into any sort of fire-rated assembly, and the intent of IRC 302.6 is to provide a degree of fire separation between the house and the garage:

Square D™ panelboards and load centers by Schneider Electric™ are not third-party certified for firewall installations. As of the publication of this article, we are not aware of any other manufacturer of panels that have successfully evaluated the use of panelboards within a fire wall.

Square D has investigated fire ratings for panels in the past with unsuccessful results. The temperature on the “unexposed” side of the wall must remain below a certain value over a specified period of time. The problem with panelboards (or any other device with a metal enclosure) is that the heat transfer is very rapid and the temperature on the unexposed sides quickly exceeds the allowable limits.

If a wall is required to have a particular hourly fire rating, then the entire wall assembly, which includes all its individual components, is expected to maintain that rating. When you place a panelboard or load center in the wall, you introduce a foreign component that has not been evaluated to insure the integrity of the wall is maintained. The same is true for doors. For example, UL tests door assemblies for fire ratings to make sure the entire wall will be resistant to fire for the required duration of time.

Square D manufactures equipment that may be used through fire walls. Take for instance busway passing through many floors in a high rise building. The UL ® Fire Directories (see reference below) provide materials and assemblies that ensure the fire would not spread up a high rise through those penetrations. Although there are methods to “Fire Stop” busway for two hours, there have not been any panelboards successfully evaluated for such purpose. Keep in mind that even if you were able to get the panelboard to pass, you then also add other materials (wire conduit, penetrations to exit the panel and fire rated wall) that would have to be considered in order to maintain the integrity of the fire rated wall assembly.

So, in order to maintain the integrity of the IRC R302.6-required fire separation, we use a surface-mounted panel instead. The penetration firestopping and ⅝" Type X drywall exceed the IRC's requirements for this wall, but penetration firestop testing assumes that the wall in question is constructed as a fully rated wall, not the "cross fingers and hope we get the 30 minutes predicted by IBC 722 calculations" basis R302.6 works from.

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    @manassehkatz-Moving2Codidact -- since the EZ-Path 22 is shorter than 24" long, no, that derate is not an issue Oct 10, 2021 at 19:10
  • Wow, great information. It looks like the EZ-Path 22 is a strait tube. Would they be mounted horizontally from the garage to the attic space above the pictured wall? (If you meant vertically, then I'll need some more explanation to understand what you mean.)
    – KJ7LNW
    Oct 11, 2021 at 2:38
  • @KJ7LNW you are correct that they'd be mounted horizontally :) (they can be used to penetrate floor-ceilings, but that's not what we need them for here) Oct 11, 2021 at 3:38

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