Hello. I am approaching the point of my crawlspace-to-basement dig out project where I will be building my retaining walls. The retaining walls are what will be giving me extra ceiling height by allowing the floor to extend below the level of the foundation footings. Naturally I want to have a good effective vapor barrier under the concrete slab. My question is how do I work a vapor barrier into the retaining wall. It seems like it should be run directly behind it and uder the upper slab (depicted by the red line in the sketch). However, is it really wise to run plastic between the wall and its footing? I'll have rebar tying it all together but still I wonder. Any thoughts? Thanks. P.S. The tan part between the retaining wall and foundation is my trying to represent gravel. I'll also have gravel under the floor slab and vapor barrier but I forgot to draw that in the picture.