Installing wood deck over concrete patio

My husband and I are wondering if it is possible to install a wood deck over a regular concrete covered patio (north facing, so almost no sunlight hits it - just a little in the morning). There is one thin crack running most of the width of it (developed about 1 year ago, got ever so slightly wider (1/16") over the next couple months, but now stable), but that is the only flaw.
We plan to screen in the patio, then "extend" it by installing a wood deck on the other side of the screening (for those times we'd like some sunshine:). We thought it would look great to place a wood deck over the covered patio, too, making it look like one large deck, half covered and screened.
The patio is currently approx. 15' x 20'.
If this is feasible, are there any special preparations we need to make to do this? Or can we just lay down some heavy-duty plastic sheeting to keep the moisture out of the wood, put down some plywood and attach the decking material to that?
Any thoughts on this???
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On May 14, 10:38 pm, snipped-for-privacy@yahoo.com wrote:

I wouldn't build any type of structure on a patio, unless it was originally built as a floating slab with thickened and extended edges to support the load of the structure and roof. That is how a free standing garage is typically built. You also don't say if you imagine connecting this screened structure to your house. Definitely don't do that because the patio will float around as the ground freezes and thaws and will crack where it connects to your house. I think the cheapest and easiest way to accomplish your stated objective would be to put support posts on concrete posthole footings around the outside of the perimeter of the patio, and build the screened structure so that it is completely independent of the patio, supported only by the load bearing posts. You can still put wood flooring on the concrete for effect if you choose to, and butt it right up to the walls but don't connect them. Build your wood deck adjacent to the structure, also not connected to the screened structure unless you're sure it is designed to carry the load along one wall. I wouldn't put plastic under the wood in this case. If you spill water or rain blows in, the plastic will keep it in contact with the wood for a long time. The concrete will at least absorb it and eventually dry. Use pressure treated wood, maybe paint the bottom with something to seal it and prevent rot. It might be easier to just put down 1x2 sleepers on the patio and build the wood floor on the sleepers. You could attach the flooring to the sleepers but not attach the sleepers to the patio so the whole thing floats.
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I'd take a concrete patio over a deck any day. Sounds to me like you are going to have a long term headache here when junk and dirt accumulates under the decking. Not to mention insect nests and mice homes under it in such a snug place. Trading in a maintenance free pad for a slab of wood that needs attention just does not make sense to me.
You also don't want plywood under a deck. Even the pressure treated stuff is not good in an application like you suggest. Sleepers on the ground would be better.
Just my thoughts, your money, your time.
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<snip>

Totally agree with Ed on the 'fashion decks' so popular now. In a few years the landfills will be loaded with treated timbers from razed decks leaching their nasties into the ground water. They might be useful for a summer cottage at the lake or similar, but in town? IMO makes much more sense to build an old fashioned screened porch (with even a porch swing) to enjoy the view of the neighbors as they struggle to power wash, sand, and stain their their seldom used ugly appurtenance. For the OP, installing a deck over the concrete patio will require a building permit and then show up as a nice little increase in next year's taxes. It's your home, your call.
Joe
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I have a small deck buit directly on top of a concrete slab.
I spent a few hours today trying to stabilize it, it needs replaced.
the wood is in fair shape, the concrete underneath is spalling and falling apart, the wood depends on the concrete. so the wood is moving and coming apart
the whole mess will have to go and it will be all concrete the next time
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