I am installing a subpanel in my attached garage and thought I had covered all the bases when running PVC conduit horizontally through the wall between the house and the garage. The wall has 5/8 fire code drywall on the garage side. The PVC conduit actually is run through the rim joist from the basement. So I recently saw some items that may apply to my situation.

  1. The 1-1/2” PVC sch 40 conduit is running perpendicular through the first-floor rim joist, I saw some discussions that this needed to be PVC sch 80 conduit for conduit running in a garage? Does that apply to the conduit running above the subpanel up the garage wall and along the ceiling?

  2. It is coming through the wall approx 4 inches off the concrete garage floor, is this an issue? Is there a height requirement? There really isn’t any horizontal conduit in the garage, since it goes immediately into an LB, and up the garage wall 54 inches into the bottom of the subpanel.

  3. Suggestions for how to maintain the firewall fire integrity around the PVC conduit, the hole drilled for the conduit is exactly the same as the OD of the conduit, and there is no gap. Should I still try to fire caulk around the conduit where it comes into the garage?

  • Can we safely presume that the garage-house separation wall has a drywall finish both sides for the whole height involved? Jan 1, 2023 at 16:32
  • Everyone thinks plastics are non-flammable. That's not true, they're made of petroleum and must burn exothermically when externally exposed to open flame - i.e. they are flammable. What plastics have is the ability to (by adding boron compounds) resist initial ignition from a smoldering source aka cigarette dropped by a person who has fallen asleep. I would suggest replacing the PVC sched 40 with RMC (merely because it has a similar outside diameter to PVC). Or if you're just using it as a pass-thru for cables, literal conduit is not required, any steel pipe would do. Jan 1, 2023 at 18:55
  • @ThreePhaseEel Correct, there is drywall on both sides, the garage side is 5/8" firerock. Not sure if this makes any difference, but my garage floor is a step down from my first floor, so where I come through to the garage from the basement, I am essentially coming through the rim joist and not the actual wall. The firerock is all the way down to the garage floor.
    – user149104
    Jan 1, 2023 at 20:00

1 Answer 1


First off, I'd use Schedule 80 for whatever's in the potential crunch zone, which'd mean using it from the LB up to the subpanel, but there's no need for it for conduit on the wall above the panel or in/on the ceiling, though. There's also no height minimum you have to worry about as long as the LB is accessible.

As to the fire caulking, though, this is not a situation where you can just use whatever and have it work. Most fire caulks are not tested for what is called a "continuous contact zero annulus" situation, only for eccentric point contact between the penetrant and the wall surface. Furthermore, those that are tested for "continuous contact zero annulus" use are not tested for that situation when a nonmetallic (pipe or conduit) penetrant is used, only with metallic (pipe or conduit) penetrants. So, you'll have to hog out the drywall opening slightly (good quality fire caulks are rated for point contact zero annulus use, so it doesn't need to be perfect) then apply your fire caulk of choice.

  • Is 1-1/2 inch sch 80 ok for the 2-2-2-4 SER cable?
    – user149104
    Jan 1, 2023 at 20:12
  • @user149104 -- are you running conduit the whole way, or only as a damage shield? If it's the former, then you should be pulling individual wires instead of trying to wrangle a cable down a conduit, and if its the latter, then since there's drywall both sides, there probably isn't a need for it at all Jan 1, 2023 at 21:00

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