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I'm trying to get things ready in my unfinished basement to frame walls and finish it. Currently, I'm trying to add solid blocking between my floor joists and sister a few joists before I start framing walls, and putting up strapping to drywall the ceiling.

The joists in my house are made from 2x12s on 16" centers. The issue I'm having is that a lot of the joists and twisted where they meet the main beam in the middle of my house and I can't seem to move them back into place. The homeowner who built the house did not install any blocking or bridging between the joists and over the past 24 years they started to twist pretty badly.

I'm having a very difficult time installing blocking between the joists because none of them are straight and I can't make cuts in the the lumber to precisely fit the space between the joists I'm trying to fill.

From everything I've read it's very important to ensure that the blocking is tight between the joists, but I have some gaps at least 1/4" after fastening the blocking in place.

Will shims help fix this if I stuff some in? Will the blocking do anything to help displace load or take some bounce out of my upstairs floor if the blocking isn't tight since I have these gaps everywhere?

I really want to fix the joists and install blocking because once everything is drywalled I ideally never want to have to rip the ceiling down to fix it again.

Any help or guidance would be greatly appreciated!

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    Twisted wood is not easy to untwist with proper space and equipment. In place almost impossible. Can you post pictures or describe the twists with measurments?
    – crip659
    Commented Feb 19 at 19:18
  • Pics with a measuring tape to show how far out would be the ideal description.
    – FreeMan
    Commented Feb 19 at 19:34
  • "I can't make cuts in the the lumber to precisely fit the space" - that's the problem. "I really want to fix the joists" - nope. stabilize as is. If it doesn't require more hammering into place then you want, then it's too small. If the first one you make seems to kinda fit everywhere; that's your template, off of which you custom fudge all the others. (also, there's no pics)
    – Mazura
    Commented Feb 19 at 21:15
  • The pics/links did not post. The amount of twist can be important, leave as is or maybe replace/repair.
    – crip659
    Commented Feb 20 at 0:25

2 Answers 2

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Some suggestions from my experience...

  • I wouldn't attempt to get everything perfectly square and straight. Over two decades your lumber has set and hardened, and you may find frustration and diminishing value in doing so. Instead, get the low-hanging fruit and trust that the design overhead will prevent catastrophe.

  • To that end, focus on blocking at the ends where the joists are supported. In addition to C-clamps and bar clamps you could use a lightweight car (scissor) jack to push off one joist and reposition another. Of course, the first needs to be stable and supported first; a block screwed well flat to the beam could hold a bottom, for example. By working one end to the other you can get things in shape and install blocking.

  • Don't try to use screws to pull warped boards into position. That usually doesn't work well in cases of heavy lumber--the first screw will pull some, but then it locks position. Subsequent screws would have to overcome the threads of that one, and so on. Position first, then add screws.

  • Your new strapping acts as bridging, so I wouldn't bother blocking in the field unless you're dealing with floor bounce or other inadequacies. The strapping will maintain joist position just fine.

  • Keep noise in mind. All blocking should be fit snugly, fastened well, and solidified with construction adhesive where appropriate. Adhesive isn't to be considered structural, but it can silence what would otherwise be very annoying squeaks and pops.

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I’m no expert, so I could be wrong, but can steam help make wooden joists more flexible? Then you could use G clamps at various intervals to twist the joists back into place, once they’ve dried from the steam, they could retain the position.

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    Yes, steaming wood is the main way it's bent. However, attempting to steam joists that are already installed will be fraught with issues. Usually, wood is placed inside a steam box where the steam is held, often for an hour or more. Nobody just waves a tea kettle around near it and expects it to soften enough to flex. There's also no guarantee whatsoever, that steamed construction lumber will hold its shape once dried. All that steam will also wander all around the basement, softening flooring above, studs in the walls, etc. Overall, not a particularly good idea.
    – FreeMan
    Commented Feb 19 at 19:33
  • Like I said “I could be wrong” I work in I.T but a family member replaced all the joists in a room which I helped with, just chucking an ideas out there. G clamps could be an idea though at intervals.
    – Matt
    Commented Feb 19 at 19:39
  • Yes, yes you did... That is the way to bend lumber, but it's probably not the way to bend 2x12s, even if they're not installed yet. Not familiar with a G-clamp. C-clamps, F-clamps, parallel clamps, yes, G-clamps, not so much... Huh. Guess that's another name for a C-clamp. Not sure how you'd use one to straighten a joist out in this situation, but I'm always open to new ideas.
    – FreeMan
    Commented Feb 19 at 19:43
  • Wild guesses from inexperienced laypeople are not helpful in structural matters. Maybe if we were trying to remove wallpaper.... Yeah, "C clamp".
    – isherwood
    Commented Feb 19 at 20:17
  • Lol, guess you’ve never used a G clamp before then, my family member has over 40 years experience with wood work (do you know what a pattern maker is?) and uses clamps.
    – Matt
    Commented Feb 19 at 20:58

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