I walked around a house for sale today. It has a wonderful multi-tiered deck, at least I thought it was wonderful until I looked up from underneath at the "ceiling" of the lower decks. It looks like they put plywood under the decking to prevent water flowing through onto the heads of people on the lower, but now the plywood is all moldy. I have included the picture below. Is this a "run away from" situation , "don't touch that house", or is this something that can be easily remedied? Can/should this plywood be removed and replaced with something better? There are about 1000 sf of decking that has this plywood underneath it.

{{!gwi}}