Unlevel sub floor

Have finally finished Kitchen, Living room area and moving upstairs. Putting 3/4 nailed hardwood down. Just took off the press board flooring that had a lot of squeaks. Found there is a dip of 1/2 inch in a 4 foot span between rafters. Am going with 3/4 sub floor and wondering if I should use a filler in the dips There is also another place with 1/4 dip. All this in a 12 foot hall way. With press board out squeaks went away. Planing on using 3/4 on top of the 1/2 already down. Should I use plywood or something else? No glue between layers and felt on top 3/4 layer? Thanks ahead of time.

 

Which direction do the floor joists go? Hopefully, perpendicular to the lay of the hardwood. Also, are you using random length hardwood or are all the pieces the same? Smaller pieces strategically used can help circumnavigate small dips and oddities. Good move getting rid of the particle board, its is good for nothing except giving me work when it eventually gets wet and needs to be removed.

3/4" T&G Advantech (big orange calls it Home Advantage) is the current industry standard for premium subfloor material. It may well bridge any gaps you have in the current framing and smooth things out. I would use 15# felt between the 1/2" and the 3/4" to cut down on noise and use deck screws to first secure the 1/2" to the joists and then the 3/4" to the 1/2".

Plan well as you will have stairs and other obstacles to deal with that will require precise measurements to hit the marks. Less of an issue on stairs if you hit them perpendicular to the lay of the floor.

 

yes perpendicular to joists. random lengths. Will screw 1/2 down and 3/4 Shouldn't have to fill dips than. Was worried about 1/2 dip in a 4 foot span.

 

Floor level issues can look more dramatic than they actually are. If you have one that is slightly high, and one slightly low, then the difference between then looks like a huge issue. But in the scheme of the whole floor it is minor. Have you stretched a mason line across the whole room to see the extent of the issue as it relates to the whole room vs the small area you are checking with a level? Is it definitely a low or high joists? and not a swollen subfloor panels edge that received a lot of water from rain during the building of the house? 1/2" isn't very stiff to begin with, is it just normal flex between the joists? I would probably put down the 3/4" and see what we are looking at and then address if we need to sand/plane the high joists or if we can work with it.

 

Hall 12 foot long, Have 3 level house and hall is eye level. Ran string line this AM and floor has high spot almost in center. Floor tapers down both sides of high spot about 1/2 inch each way. Not to worried about this but in front of one door way the floor dips to 7/8 inch. Thinking with that much dip it might squeak. Was squeaking with old press board and bedroom in same location squeaks. For bedroom thinking of getting the break off screws for now.
answer may show up 2 X did not post first time I tried.

 

Have had instances where it was not the floor that was squeaking, it was the wall that was moving in relation to the floor. Basically, riding a smooth shanked nail that missed a floor joist and was free floating in the subfloor. As the floor flexed, the nail squeaked. Used shims under the base plate on the wall to quiet things down.

Your call if adjusting the high joist will solve the problem. Now is of course the time to do this. Take the 1/2" out the nearest joist on either side. You can sister a nailing surface, or try to split the joists. Then you are open to wittle down the high joists to where it will work. Since you are adding 3/4" on top, you may be able to reuse the section of ply that you pulled.