I always though pressure treated lumber was to repel wood eating critters, not moisture rot. This is an important distinction. Here in VA where I live they like bare lumber on their decks for whatever reason. It is probably pressure treated, but if it is not weather proofed the sun in exterior exposed lumber will make it dry rot and in damp areas will let it mold. Anyone know the distinction?
Treatment serves two functions. It stops termites and it kills fungi which cause rot. There’s very little experience/history with the replacement treatments. I’m seeing something green growing on treated decking locally that was installed less than a year ago.
I’ve had some of the 2.4 pcf stuff in a similar application and it looks the same after 10+ years. In a freshwater environment, the 2.4 pcf treated lumber will be good for many decades.
Treated lumber is not treated with fungicide, and will still mold and dry rot. It will resist insects, however.