Porch floor rotted-need a better idea

About 7 years ago, we converted an open deck to a covered screen porch. I cut some corners & used OSB interior plywood for floor - now it's rotting out (even with 2 coats of exterior latex on it).
Obvious replacement is treated plywood, but I wanted to look at other options. I'm looking for suggestions, sources, materials for an elevated porch floor that can be built on top of a wood frame - and will be water and decay resistant.
Any ideas?
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Treated ply will not rot soon , it may eventualy but will still mold from rain, maybe afecting the support. You need to use a floor that will dry out and have air movement throughout the undereath, treated or cedar plank with air spacing is usualy used. If this is above joists , first layer it should not be a problem. Air circulation above , under and sides is important for a deck. Closed in decks on all sides just trap moisture.
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Francis Rowe wrote:

I would suggest that for a start make sure the area under the floor is well ventilated. I suspect this was part of your problem. The other part was that interior plywood is very sensitive to moisture and will delaminate very easy if damp.
How much are you willing to pay? There are some great hardwoods you could use, but some are very expensive.
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Joseph Meehan

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Is the original decking still there? If so perhaps you could use that and just staple some screening to the underside to keep the bugs out.
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Francis Rowe wrote:

porch. I

rotting
elevated
water and

Nexwood makes a nice T&G composite 1x6 decking. It'd keep out the bugs, no painting involved, and it will last. Simple to install and no visible fasteners (except up against the building - and then they're smallish). A very small amount of water will drip down between the Nexwood planks, but unless you need perfectly waterproof, it's a very good choice.
R
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Francis, Is your porch installed over closed crawlspace. Where are you located. Answer for you is somewhatt location dependent.
Stretch
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Sorry, folks - I left out some important details
The porch is 10 ft up with plenty of ventilation underneath. In the conversion, we removed the original (6 x 1-1/4 in round-nose) decking & laid 3/4 in OSB T&G plywood. Then erected open stud walls, built a roof (lean-to off the house roof), and screened all around.
Now the floor is delaminating & rotting, and the base plates for the studs are rotting as well. This is due to collection of rainwater on the floor during storms
RicodJour's NexWood suggestion is intriguing, but there don't seem to be any NexWood dealers in my neighborhood (Georgia). I have seen similar produts locally, though - this is worth a look-see.
Still open to other suggestions, though. Is there any way I can put down a concrete subfloor over wooden framing?
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"The porch is 10 ft up with plenty of ventilation underneath. In the conversion, we removed the original (6 x 1-1/4 in round-nose) decking & laid 3/4 in OSB T&G plywood. Then erected open stud walls, built a roof
(lean-to off the house roof), and screened all around.
Now the floor is delaminating & rotting, and the base plates for the studs are rotting as well. This is due to collection of rainwater on the floor during storms
RicodJour's NexWood suggestion is intriguing, but there don't seem to be any NexWood dealers in my neighborhood (Georgia). I have seen similar produts locally, though - this is worth a look-see.
Still open to other suggestions, though. Is there any way I can put down a concrete subfloor over wooden framing? "
I'd suggest instead of throwing good money after bad, you get some estimates from professionals for straightening this out. Particularly since you're now thinking about putting a concrete floor 10' up in the air, supported by God knows what. This is starting to sound like one of those DIY decks that collapses every so often with 10 people on it, sending them into the street. I'll bet you didn't even have a building permit or inspection when you did the original conversion that lasted all of 7 years, did you?
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Forget concrete unless you dont mind puting in all new and extra supports of steel. Go back to planking treated, cedar, or one of the new composits. But many composits flex and will need additional supports.
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