Exterior plywood for deck surface

I want to replace my 10' X 10' deck boards with exterior treated plywood to make the area under the deck water tight, I would .like to then put outdoor carpet/astro turf on the deck. I then plan to enclose the area under this deck with an enclosed area with vinyl windows and storm doors to extend the seasons a bit. The entry into this new room from my house is from my walk out basement out to the level where my pool is.
So the question is, will the plywood stand up over some years to being almost flat and not delaminate etc.
Thanks, Rich
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found when redecking my pontoon boat that you can't apply carpet glue to treated plywood and expect it to work. I would recommend regular decking and then use the product that is designed to be installed under decking to funnel the water out and onto the patio. My mother has this under her deck and it remains dry in the patio area right under it. Kind of looks like metal roofing like mobile home patio covers.
Tom G.
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Rich wrote:

As Tom G says, the problem is flashing edges and sealing joints. TB
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I would suggest then that you are building a roof, so you should treat the problem as a flat roof with a deck on top.
Cheers, Wayne
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Exterior grade plywood is water resistant, not water tight. If all it took to make a watertight flat surface was some exterior plywood, you'd see lots of roofs made out of that (and nothing over it).
-Tim
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Just last year we replaced a deck at our cabin made of untreated 3/4" plywood. It was simply nailed to the deck structure and painted...it last about 15 years before delaminating enough to require replacement. The structure in question is in the Blue Mountain in Oregon at about 5,000' so gets a good amount of snow each winter but is dry and hot most of the summer. While I wouldn't use this approach at home, it was a cheap and effective way to build for the cabin. I suspect that treated, seam sealed, and painted plywood would last quite a while longer, especially if it's shielded from the rain as you describe.
-kiwanda
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replying to Kiwanda, Richard Gregory; Evans,Ga wrote:

We had the standard pressure treated 2x8 for the decking...It was hard to main- tain since water can easily seep thru the space gap...To replace this system, we remove every other plank and layed 3/4" 4x8 sheets of pressure treated on top. To make the joints water tight, we bevel about 1/4" off on all outer edges.. The space was filled/sealed w/ Bondo w/ fiber strands....Used a high rated bonding/ sealer primer & finished w/ exterior grade floor paint.....There is a roof cover overhead....The decking does have about 1% slope....So far, the joints have not open//s
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Rich, I've recently built a deck very similar to what you're describing. Key things: - gotta have slope for drainage. 4" over 14' is what I have - I plywooded, then put a modified torch down roofing membrane ($200/square). Square is 100sft - For decking, you can lay down sleepers above the old joist (1x4 or 2x4), and deck on top of that - some people build panels that they lay down on top of the roofing membrane, so it's floating and can be removed for cleaning and roof replacement - I'm doing something different. I'm tiling on top of the membrane. - Plan on it leaking at some time in the future. In other words, don't put hardwood flooring in the room beneath. Even avoid sheetrock in the ceiling if possible. Go with a removable ceiling so you can take it apart later, when it leaks....
good luck
Rich wrote:

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Thanks for the advise, the room below it has concrete pavers a picnic table 4 chairs and out door speakers, and will be basicly a screened in room with vinyl windows, I only have two things that can't get wet and those I can make special provisions for, if it leaks a little here or there big deal but I would still be able to use it for what I want it for. To extend the season a little and get away from the wind and the bugs.
I could add 2X4 by 10' ripped corner to corner for the proper slant and water shed away from the house easily enough. How noticeable is 3.5" over 10'?
Rich

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