In reading many of the advice posts it appears that in a mild climate like the Southern Oregon Coast most of the slab loss will be through the foundation if the slab is not isolated from it. That's based on a worst case air temp of 30F and ground temp of 50F. The structure is a 105' by 60' steel building with 20' wall sitting on a 2' concrete stem wall. The interior is completely insulated with R5 except for windows and light panels. Here are the things that worry me. 1) We have two seasons here, 6 months of rain, and 6 months of road repair. What do I need to put under the slab to keep it dry? The pad is part excavation part fill on the side of a hill. I put a French drain around the two sides that are below the banks. How much rock above grade do I need under the slab? 2) And my main question is; how does one insulate the slab from the foundation/stem wall? The method I have seen described here is 2' rigid foam running from the surface of the slab down to the frost line. We don't have a frost line here but the insulation will nevertheless be useful. What does one do with 2" of foam separating the slab from the stem wall? Seems it would be a dirt catcher, which in turn would diminish the R value. I am considering extending the foam to the top of the stem wall, covering it with exterior plywood, and capping the entire top of the stem wall with flashing. Any advice will be gratefully accepted.