BBlackford

Cadabra: I hardly think appropriate water proofing over a living space is "unnecessary." In addition, being a builder in California, we frequently have to "over build" for seismic reasons. Hence, the expense. Also, I'll take the extra expense to prevent water intrusion any day. I've seen way too many cases of water damage and the cost of repairing it far exceeds the cost of properly waterproofing in the first place.

Ipe is renewable if you buy form a certified seller.

I have done concrete over wood subdecks. They look good, they will last a long time if done properly, but they are expensive. Start with pressure treated joists (standard for any deck). Put down a surface of pressure treated plywood. Then install a water proofing system. There are many. I happen to prefer liquid Bituthane. Put down a layer of protection board or drain board, then pour your concrete. It is important to allow for drainage of water that will move through the concrete as well as surface drainage.

You can then apply stone to that surface if you wish, or instead of pouring concrete you can put a mortar float down and then put tile or stone on top. If you are going to use a float it is important to frame at 16" o.c. and use substantial joists in any case.

Redwood is no longer a viable decking material in my opinion. It doens't have the rot resistance because it isn't coming out of old growth trees anymore. I don't like the look of the plastic. With the cost the same as Ipe, for me, its a no brainer. Use the wood. It is a lifetime deck material, doesn't splinter, ages beautifully and wears like iron. I also question the actual "greeness" of these type of products. If they're not being made form 100% recycled materials, they are using oil and contributing to the shortage of that material. Wood is a renewable resource plastic is not.