Persistent squeak (probably) at subfloor/bottom plate junction
OK, construction/engineering wonks, I’ve got a challenge for you:
The floor in the bedroom we’re redoing squeaks. After removing carpet, we found 1/2″ particle board underlayment over 3/4″ plywood over joists. Added screws through all layers; still squeaks. Removed the particleboard in the worst area, exposing the plywood subfloor. Still squeaks. Added screws through the subfloor into the joists. Still squeaks.
So now it gets interesting: most noise seems to come from the floor/exterior wall junction. Also, this room is over the garage (meaning: fairly long beam/joist spans), raising the possibility that even though the floor’s reasonably (though not perfectly) level, there’s some deflection causing the joists to rise slightly at the ends. (See drawing below of what I hypothesize might be happening.)
Garage ceiling is finished, so can’t work from below without removing drywall. Photo shows beam running crosswise in garage ceiling; joists run perpendicular from the beam to another beam over the car door.
So I removed some drywall to look at the exterior wall framing bottom plate (which rests on the subfloor sheathing), and saw a not-huge but still noticeable gap (photo). So, I drove shims under the bottom plate in several places, and was surprised that they went all the way under the base plate with fairly moderate tapping. Then I drove some screws at an angle through the base plate into the subfloor to snug the plate against the shims. (Photo)
STILL SQUEAKS.
Options I’m considering:
1. Floor fix: cut out a section of subfloor (starting about 6″ away from the wall), look for/fix any obvious defects, cross-brace the heck out of the joists, sister-frame around the opening, replace subfloor.
2. Wall framing fix: remove more drywall, confirm framing is still in place/correct, then drive big Spax lag screws through baseplate and subfloor into joists to make sure the whole dang thing’s rock solid.
Any other ideas? Any ways I could screw up and cause a bigger (structural) problem? Do I need a structural engineering consult? I’m open to all suggestions, up to and including “burn it, take the insurance money, and move to Bali.” 
Thanks, all!
Replies
Hi
I had a Similar problem with an Internal partition on my main floor. I tried all of the standard solutions and nothing worked. Fortunately I have access to the underside of the osb flooring so I drove flooring screws up through the floor into the plate of the wall. Made sure to use flooring screws to assure that the floor was pulled tightly to the plate. This didn’t fix everything however. Further examination showed that there were two sistered joists nearby. They were not tied together so I’d used a number of bolts to draw them together so that they would move in unison as the floor flexed. This solved the problem as I guess the joists would rub against each other before they were fixed. Not sure these ideas help your situation but I thought that I would describe a somewhat similar problem and how I fixed it.