Installing floating wood floor, need advice on fixing uneven floorboards
Hi everyone, first post to the site, hoping to find some advice on this issue and this forum seemed like a good place to start.
I just bought a place and we're putting in some floating wood floors on the main level. I've hit a bump in the road and feel like I'm at a point where I need to consider if this is stilla DIY project, or if I need to get professionals on this.
After removing all the previous flooring (carpet / laminate), one area of the house is pretty uneven and the floorboards are definitely sagging there. My best guess is that it looks like the house settling. No visible evidence of moisture damage. The house has a center beam and basically things "behind" that beam (the back half of the house) are all good and relatively even. However looking into the front, left corner of the house, there is sagging right after that beam. The area that's uneven due to the sagging is roughly 6ft by 4ft (rough estimate), and the sagging from the beam is about 1/2in - 1in deep.
Here's a link to a crappy sketch of the area. The gray is where the leveling compound already exists. The red line is the house's beam (joists are perpendicular to it). Blue is roughly the area that's uneven to where the beam/compound is.
Whoever did the last run of renovations laid down some self-leveling compound over the floorboards in the main trouble area, but the problem is that the sagging continues into the next room and they just blocked out that room when they laid the compound (seems idiotic to me). So on top of the sagging noted above, there's a 1/2in lip from the one room (bare floorboards) to the compound-covered board. That would be easy enough to remedy, it's just the larger area of unevenness that concerns me.
The blue area is also uneven in-and-of itself, meaning when I lay a straight edge within the room laying parallel to the beam, there is about 1/4-1/2in unevenness. Obviously the more prominent difference is noticed when laying the straight edge perpendicular to the beam, from the compound (gray) area into the other room.
It's difficult to get a full picture because the basement is fully finished, otherwise I could look underneath and consider reinforcing the joists. I'm hoping this doesn't warrant ripping up the finished basement's ceiling to jack up the house.
So here's where I'm at: Do I get some more self leveling compound and level out the adjacent room so it's at least flatter and can support the floating wood floor, or would that just add weight to the house, potentially increasing the unevenness down the road? Do I call in a pro to really assess the situation, knowing that jacking and maybe replacing the floorboards could be options? If anyone has experience dealing with this kind of stuff, I'd love to hear your advice!