Twisting joists

[tomh]

Your approach to add blocking was the right way to address twisting in the joists. Green or treated lumber will twist if not supported, and the blocking should deal with this effectively. It also helps to distribute loads across the deck.

Adding blocking at 4-foot intervals may help, but at this point the wood should be stabilizing, and probably won’t move much more. If joists are unsupported at the end due to pulling out of the hanger, you may need to replace some of them. If they are screwed to the deck, they should be fairly easy to detach and replace. If nailed, it will be easiest to cut the joist in half using a sawzall and pry it off the deck from the bottom, back out the nails then replace the joist. Again, you did everything right to this point, but lumber does move until it reaches a moisture equilibrium, and sometimes you just have to replace badly warped pieces if they don’t serve their intended structural function due to warp. Once badly warped, I know of no way to make them straight.