We’re in the process of expanding our front hallway and we’ve moved the front door some 6ft out on a new concrete slab that was just poured. The new front entrance wall was framed with double 2×6 sill plate. The bottom plate, which is sitting on the concrete slab, is pressure-treated lumber and there’s foam barrier under it. But the 2nd (top) plate is just regular lumber. We just realized we need to raise the slab height *outside* another 3 inches which means that both plates will be effectively embedded in concrete on the outside.
 
What’s recommended way of providing water/moisture barrier between the wood and concrete in this case in order to avoid long-term rot? My contractor suggested applying liquid flashing (Prosoco, Soprema) and then installing metal flashing as well before pouring that additional 3″ of concrete.

Any other suggestions? Would an inch of ISO insulation between the wood and concrete help (ie creating a channel of sorts on the outside wall perimeter)?

Thanks