The house I recently purchased, built in 1973, has particle board subfloors. To clarify, this is not OSB and this is not just a particle board overlay over plywood -- the entire subfloor is 3/4" particle board (looks like oatmeal).
There are several issues with this subfloor: the floors are creaky and warped in places and I've been strongly advised not to install hardwood floors over particle board, as they cannot hold nails and will deteriorate if water is spilled. I purchased hardwood floors (pre-finished 3/4"). Now I need to either 1. remove the particle board or 2. nail plywood over the particle board. I'm opting to remove it because with option "2" I'll end up with undesirable height differences in places.
The problem with removing it is the existing subfloor runs under the interior walls, so once I cut it out and add new, there won't be any support where it overlaps the joists. Additionally, if the interior wall is not sitting on a joist, it could drop. This problem also occurs for doors and closets. To solve this I could install blocking, but then this could get very labor intensive. Another option is to cut along the joist and leave a margin of particle board along the walls. I could leave particle board in the closets since there is no load there.
Another component to this problem is in the kitchen. The previous seller put in new cabinetry and granite counter tops. I don't really want to tear out the cabinets due to the expense. I could cut the subfloor out around the cabinet but then have the problem of what is supporting the cabinets (parallel with joists).
I'd appreciate to hear from anyone that has ideas on the best way to proceed.