New Deck over Old deck?
 

I just purchased a home with a deck. The previous owner built a new
screen room on top of the 20 year old deck without doing anything to
renew the deck. I have tried pressure washing it but the boards are
in poor shape. Turning or replacing the deck boards is not an option
without dis-assembling the entire screen room. Can I purchase 5/4x6
PT boards and just install them on top of the old deck? If so, how
long would I have to wait before I could stain them considering they
are shaded by roof of the screen room?