I have done slab on grade projects where the posts sit on the concrete slab (with a metal or treated wood stand off) so the owner could use radiant floor heat in the slab. The tubing for the radiant floor was placed prior to pouring the slab, so an additional topping was not needed. Be sure to insulate under the slab. We used metal straps cast into the foundation at the outside face of each perimeter post to anchor the frame to the foundation. The straps are then hidden when the exterior wall goes up. How close is grade in relation to the top of the slab? This can impact exactly what the perimeter detail would be as you don't want the wood to be in direct contact with ground. If it is too close, you may want to consider a concrete or block curb at the perimeter to keep the wood construction away from grade. Feel free to send me an email if you want to discuss this in more detail. Best of luck.
