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I'm replaceing a portion of drywall on the ceiling between floors 1 and 2. For the drywall, I plan to add backer boards on edges. The issue is there are joist blocker boards running perpendicular between the joists. Can I "legally" notch a quarter inch within the center one-third of the perpendicular joist blocker board?enter image description here

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  • Why do you need to notch? Can you not just install drywall over the joists and blocking? Your drywall backing does not have to run full length of the seams.
    – P2000
    May 13, 2021 at 4:10
  • @P2000 thx for quick reply. The backer boards serve the purpose of "sucking up" the two joined drywall pieces (existing and new at the joint) to reduce the hump. If the joist block prevents any part of the joint from pulling up as intended then I'll still have a hump when taping and mudding. This is my first time using backer boards for joints so don't know how much 2" of a flush joist block might affect the intended pulling up part of the joint between the existing and new pieces.
    – habrockc
    May 13, 2021 at 4:17
  • Is this a special kind of backer board? Usually we'd use a piece of 1x lumber or some plywood strips to suck-up and align the drywall. If the blocking is uneven at the bottom, then back around it and don't screw at the blocking. Would that work for you?
    – P2000
    May 13, 2021 at 4:44
  • There is commercially available OSB backer board which has a depression in the middle to create a depression in the drywall seam screwed to it. May 13, 2021 at 17:40

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You are adding nailing edges to the edges of the existing drywall to provide support for the edge of the new drywall sheet and the edge of the existing. A lot of people will just get some 1x4 and span the old sheet to the new sheet. The two sheets then align at the joint. They might not be "sucked up" as much as if you adding a nailing edge that was connected to the joists but sheets of drywall are typically supported 16" on center so at most the existing sheet will have support < 16" away and the new sheet will have support < 16" away. The 1x4 between the sheets then lends support from one sheet to the other. These pieces don't even have to be continuous. You also have texture on the ceiling which works to hide all kinds of defects so your work can be even less precise.

As far as your question goes, you can notch the blocking between the joists. The solid blocking between the joists allows your floor assembly to work as a single unit. Often cross bridging is installed instead of solid blocking and they have comparable performance. Blocking is also routinely knocked out by plumbers. A notch to the bottom of the blocking is not going to effect the function. The bottom of the blocking is not being loaded in tension. If you are worried about it

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  • short answer, Yes, you can just plane the protruding edge of that blocker board flush with the joist May 13, 2021 at 15:27
  • Or even notch the blocking 3/4" above the joist to allow the backer board to be inserted under the blocking. May 13, 2021 at 17:47
  • Agree with this answer. To be clear it's not "backer board", just backing, which does not have to be continuous.
    – P2000
    May 13, 2021 at 19:15
  • Thanks everyone for your input. I replaced the drywall but am still unsure about how to finish a corner piece that is sticking out (hangs lower than existing ceiling) that I can't force up any further without crumbling the drywall. I asked in a new question as this specific post is considered resolved. (<diy.stackexchange.com/questions/224498/…).
    – habrockc
    May 19, 2021 at 2:30

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