We have a tree deck ( or tree house) supported by three trees and one post.

The structure is still good, but the floor ( 1" ply) is completely rotted. It is rotted to the point that it cannot support my weight.

I am wondering if I need to remove the ply and then put a new one or if I can put another layer of 1" ply on top of the rotthn ply? It will still be fastened to the frame under.

The reason is, to remove and put new ply, I will need to remove all the railing and then install those again. With other things and a short summer in new england, difficult to get completed.

 

I would remove what is there. Getting back to smooth, clean framing will make installing new much easier. I would not use ply as it doesn't really hold up well outdoors. I would consider decking material/boards.