Bought a house Friday. House was built in 1975. Carpet with particleboard beneath looks to be relatively new. I pulled up the carpet and the particle board is in great shape. No stains or water damange. I think it's 3/4" but haven't actually measured. There's a gap between it and the wall so I can measure it next time I am there. I am leaning towards a Kahrs 5/8" click-lock in the Nouveau Collection. I have used their product in the past. I contacted them and they said that it would be acceptable over particleboard if it's in good shape:
"If the particle board is indeed ¾” and is firm, flat, and free of any moisture or damage then it can be used under a floating installation."
This is a big expensive project and I don't want to be sorry afterwards. In fact, my approach to house projects is generally to strive to do things that will last indefinitely. Would it be a mistake to leave the particleboard as the underlayment?
Edit: In one room I will probably install luxury vinyl so I have same question about that over particleboard.