I had to remove portions of the existing subfloor chipboard panels (18mm depth), which now I need to replace (I already bought a new P5 panel).

The problem is that one edge of the hole is irregular, and I'm worried that parts of the new chipboard won't have sufficient resting contact with the joists to provide enough support. Particularly around the lower-right corner in the pics, where the exposed joist surface is really thin.

What is a good strategy in these situations? I would really want to avoid removing the surrounding subfloor. Thanks![enter image description here]1

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  1. Cut your new patch to a size that would lap the framing halfway.
  2. Lay it in place and trace it.
  3. Cut out the old subfloor to the trace line with your circular saw set to a suitable depth.

While you could add framing blocking, that's sometimes easier said than done in tight areas.

  • Thanks, I'll probably do follow your advice, because as you say adding support to the joists looks more complicated. One question, though: the nails fixing the other planks are already halfway the joists, which hampers the plan. Should I move them closer to the joist edge? And where do I place the ones for the new plank? Thanks – anon Feb 20 '20 at 12:47
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    Just cut out according to plan and renail as needed. Construction adhesive is helpful in reducing the chance of squeaks. – isherwood Feb 20 '20 at 13:20
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    It's not really calculated by area. Assuming framing to code, you should ideally have 1/2" (12mm) bearing on any edge (or tonge-and-groove support in the case of perpendicular seams). I'm not sure how code is worded, but that's enough. – isherwood Feb 20 '20 at 18:54
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    Well, collapse is the consequence. All you'd need to do is float scrap lumber under the rest of the seam and screw it to both sides. – isherwood Mar 10 '20 at 21:35
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    I don't know what a noggin is, but if you're referring to the blocks, I suggested that you float them. That means screw them to both sides of the sheathing and nothing else. They'll effectively transfer and share load. – isherwood Mar 11 '20 at 17:47

Just add (nail, screw, and/or glue) additional framing material to the side face of the joist to provide more bearing area for the subfloor.

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