I'm replacing hardwood flooring but the subfloor isn't flat. In the area above this picture, I can slide two fingers under a 6 foot framing level that's laying perpendicular to the joists. That spot, where the sag is the worst (circled in red). To level the floor, I'm anticipating buying a temporary screwjack to raise the offending joist about a half to 3/4 of an inch, then sistering it across the entire span, then removing the screwjack. As you can see the staggered blocking (yellow arrow) interferes along the span, and there is another block on the opposite side. Can I simply remove these blockings?

I'm also interested in alternative ideas for fixing the sag. I've read of shimming with roofing shingles but that strikes me as adding quite a lot of weight.

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  • Also a hat tip for any advice on working around the ductwork, which conveniently, passes through exactly where I need to raise the floor the most..
    – elrobis
    Jul 21, 2018 at 17:49
  • 1
    Although not an expert, I would think you would want to make plywood pads and jack in a few spots, then sister more than that single joist because the joists adjacent to the problem area could be contributing to the issue (by not contributing support). Jul 21, 2018 at 17:57
  • Makes sense. That's a good idea--thanks for commenting!
    – elrobis
    Jul 21, 2018 at 18:00

1 Answer 1


Yes, you can remove the blocking. Blocking is NOT structural.

Blocking is only used to keep structural members plumb so they don’t lay over to one side when “fully” loaded.

Actually, blocking is not required until the structural member gets to a ratio of 6:1 (i.e.: 2x12, etc.) (See IRC R502.7.1)

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