Partial sub floor replacement

[69Northland]

I ripped the old carpet and pad up from the 69 Northland. Only 2 bad places that need new floor. About a 2-2x3 spots near the 2 main room vents(12' across here) . It broke through right next to the vents. I'm thinking 3/4" plywood. Set the circular saw to 7/8"? also should I screw or nail new flooring?

Not a carpenter but ready to try.

[ponch37300]

I set circular saw to just a hair over 3/4" and cut the square outline. Subfloor can be a real bear to get up. I also make a cut running parallel with the floor joists in between each joist. Then you can push in on one side and pull up on the other. This seemed to work better then just using a prybar. Then hope they didn't use a glue between the joists and subfloor. Once out pull all the staples or nails out. Cut your new piece and I screw it down, no chance of nail squeaks later on. I also add some 2x4 or 2x6 blocking between the joists to support the new seam. Just cut some blocks and screw them flat halfway under the old subfloor, screwing threw the subfloor into the blocks. Then there will be half the block sticking out for the new subfloor to sit on and you can screw the new subfloor to this blocking along with the floor joists. I just found that if you step right at the seam of the old floor and new floor in the middle of the floor joists it would flex, the blocking is quick, easy, and cheap and will prevent this.

Here's a rough sketch of what I mean with the blocking,

subfloor replacement.png