Guitarsoup said:
After the posts rotted out on the deck that came with our house, I was looking at doing this, but couldn't find a way to not have wooden posts under it that would still need to be replaced. The top boards would be composite, but all the framing underneath is still wood and still my concern.
Treated lumber with joist tape on top would help with longevity. Using metal post bases that keep the posts up off of the ground instead of embedding them in concrete make it better, or you could do helical piers or something like that.
You can also look into framing it in steel and using the joist tape. That would probably be the longest lasting option. It can also let you do longer spans.
I agree that if I was springing for composite decking, I would only want to put it onto a structure that would last at least as long as the decking.