Decks, Patios, Porches and Docks - Wood Boards over Concrete Patio

I would like to cover an existing concrete patio with wood decking. The space between my exisiting concrete and the patio door is 2.5 inches. The concrete patio has good water drainage and there is a roof overhang protecting the patio door. The concrete at the patio door never gets wet during rainfalls now, so I think I can bring the wood decking all the way up to floor height without risking water coming into the house. I've seen this done in my area, which is Northern California. The patio is about 300 square feet, and is surrounded by the house on three sides. The joist space is 16 feet.

I understand that this can be done by placing joists on the concrete which essentially float freely on the concrete. The decking is then nailed to the joists.
Will this method work?
If so, what size wood should I use for the joists, and centered how far apart. I was thinking 1X4, laid flat, 16 inches apart.
What size wood should I use for for the deck? I was thinking of someting called 5X4, which I understand is 1 inch deep.
Should I attach metal flashing and a ledger to the sides of the house, to protect against water collecting against the side of the house?
Thanks,
Bernardo

First, no matter what kind of wood you use for "joists" under the decking, it is going to rot if it lays directly on the concrete. Fir or pine might last 2 years. Redwood or cedar might last 5 years. A pressure treated 2X, maybe 6 or 7 years. If you use a 5/4 decking material, you will be placing these "joists" at 12" O.C.

That is a lot of wood, a lot of work, and a lot of money for something you will replacing every few years.

Flashing maybe, but forget the ledger. That would be just more more piece of wood you would be replacing. With the "joists" sitting directly on a concrete slab, the ledger certainly isn't needed for support!

Thank you. Your message is clear and concise. If I proceed, I do so at my own peril, knowing that I will be replacing the wood in 6-7 years.
Bernardo

Before I give up on this idea, here's a thought. Why not use plastic lumber for the "joists"? I understand platic lumber won't rot. I also understand plastyic lumber is more springy than wood and not used for weight bearing applications, but that's hardly an issue in this instance, where it is applied directly over the concrete pad. Any thoughts?
Bernardo

"Plastic lumber" -- you are referring to a composite, like Trex.

No. It's fine for an application like a mud sill on a concrete stem wall. There, it has no water getting to it that can be trapped under it and cause it to mildew. That's what would happen in your application. And, before you think about placing spacers under it, to provide an air space, again, no -- it would sag between the spacers, eliminating the air space along with creating waves in your deck.

Some houses just weren't meant to have decks.

What about building a deck the "right" way with a section cut out near the door? Basically a 4'x6' or what ever size you choose, section in front of the door. Use your idea with the boards directly on the concrete patio for this small section. Then one step up to the main section of the deck. This way you will only need to replace the small section every 3-6 years. It's easier to replace a 24 sqft deck than a 300 sqft deck. If you replaced it on a schedule of every 3-4 years regardless of condition, you might even be able to save the decking on the small deck so it will continue to match the fading and color of the other deck.

Andret's idea would work just fine. In fact, you could even leave the section (4' X 6' or so) at the door without any decking -- just the concrete.

You could step it up just 7", or you could designed it with one step between the slab and height of the deck, for a 14" rise. But that might be too high around the edges where you probably have eaves coming off of the house.