I would use either insulation or specify free draining material to the frost depth. Insulation rule of thumb, 1"=1' of grade cover. Ofcourse depending on the R value of the material. If you use gran. material make sure there is a weeping tile at the bottom to get any water away.
Canadian codes does not alow 1 1/2" deck to be used as diaphragm. We put plywood band or steel plate bracing on top. 3" deck, we use lateral bolts to increase the capacity, if you can not have them running diagonlay. If you need I email you parts of the code.
ah Vulcraft. that is thier standard answer. they hardly keep any records. I have always taken the conservative approach to joists. In Canada thay are exposeed to the design live laod and I have seen many problems. They are designed very sharply. I avoid overstresing them more than 2%. Reinforce...
