Fixing bouncy floor with sistered joists- do I need to jack?

Are the present joists sagged? if so, then yes, Carriage bolts are usually used for attaching.

Here is another method

Unless they are sagging, I would not. Also, if it's just a bounce issue, I'd sister every other one first, that's probably enough.

Cross bracing too. Took the bounce out of my deck.

I'll second the cross bracing.All the cross bracing under my dining room was loose and "wonky" - before I put down the new hardwood the floor had some give in it, and squeaked. I screwed down the sub-floor, which helped - but then I screwed all the cross-bracing tightly in position, and it was lioke a whole new floor. No give. No squeak - and NO sistered joists required

replying to Kevin W., Iggy wrote: I'd agree...don't jack unless you're fixing a problem (creates squeaks) and add bridging. One bridging I'll be trying out is IBS2000's design, as I haven't found the traditional methods to be of any value beyond stopping twisting. See - IBS2000 Fix for Bouncy Floors

The X bracing is the only bracing we ever use up here.

replying to Clare Snyder, Iggy wrote: That's all I've ever had in any of my places. But, old (with full dimension lumber) and especially new places (with Glue-Lam and wooden I-Beam) with longer spans have always been quite bouncy and even saggy under rather lightweight things like a refrigerator. I thought when they went to solid block bridging that there was actually science behind it, but nope not a single thing changed. Therefore, I find the IBS2000 videos very credible. I haven't experienced nor witnessed a Floor Truss place yet, but I do hear good things and the IBS2000 is much like a truss in its engineering.