Hi all! I had gotten some suggestions a few weeks ago, but I have more info now on how the floors are sagging. I mapped out the floor elevations every 2 feet (in a grid pattern). Found that it looks like a sack of potatoes - - it goes up, then down, up then down. (Sometimes down then up - - not a straight-line sag at all.) Mostly "up" at the edges of the room, then down in the middle, but to varying degrees.
It looks like the source of the problem is the air handlers that are hung from the joists... everywhere I have an airhandler, I have a sag. The tile floors in the house seem mostly level, so I'm guessing they were laid after the joists sagged. I have 2 bedrooms, a den, and a hallway that sag; all with hardwood floors. Since the floors are not uniformly sagging, I'm hesitant to jack up the joists, since it would have to be fairly precise to fix the "sack of potatoes" look.
Is it worth thinking about supporting the joists where they are now (sagged), then ripping up the existing flooring and subflooring, then sistering a new set of joists to level, then re-laying new subflooring and flooring?? (The flooring just needed to be refinished if they were level, so it seems like a shame to rip it up, but it's not like just 1 or 2 joists need to be lifted, or all joists the same amount of lifting.)
Whaddayathink? What would you do?
P.S. I do have some leeway in the height of the finished floors - - the tile floors that lead to the sagging hardwood areas are all a pretty good bit above the hardwood floor elevation, so if I add a (shimmed) sheet of thin plywood on top of the current finished hardwood, then a new layer of hardwood, there might not be a big change in elevation from the tile floor surfaces leading into the sagging rooms.... Just a lot of wasted wood, but if that's the easy answer, I'm all for it! If that's the best idea, how would I do the shimming, since they'd all be different thicknesses everywhere??