I have a 10 x 11 front porch. It’s covered by a roof. There’s a room in my basement below it. Currently it’s 3/4 thick tongue and groove floor that is also the ceiling of the room below. It’s the opposite of waterproof and insulated. I waterproofed the whole foundation in the spring and want to finish the basement and use this room for storage. 

I live in Ohio. So I have freeze and thaw to deal with. Also I’m limited on space. Head space below and space below the bottom of my front door above (there’s about 1” below my door to the top of the floor). Right now there are 2×6 joists with the 3/4 T&G on top. I’d like to keep within this 6-1/4ish thick space. 

im thinking I have enough room for 2” rigid foam and 4” of concrete. I’m unsure of all the details. 

can the concrete support itself with a well constructed rebar reinforcement inside it?

could I put 2” foam, a waterproof membrane then concrete so that there is a total thermal break between the pad and the room? The foam would be between the concrete and the supporting wall structure all the around the perimeter. I don’t feel like the foam could handle that but I think it would be the best insulating option 

im thinking of wrapping a membrane up the walls of the house as the flashing so that I have a continuous waterproof membrane up the wall a bit and completely under the pad. I’d call the joint between the concrete and the house also. 

what am I doing right and wrong?

anyone have a cutaway pic showing a similar situation that details flashing, insulation, etc?

thanks