I'm prepping my yard for sod that I'll install in about a month (I live in So. Cal) and need a few questions answered before I begin. My existing soil doesn't look bad, but just to be safe, I will remove a few inches of the existing soil, then will add new top soil. I already tilled the area once to aid in removal and leveling. So here's my questions: Do I need to till again to get the new soil mixed into the existing soil? Or is this optional? Does sod have a "standard" thickness? I need to know this so I can level the rolled top soil to the correct grade so the sod is level in height with my walkway and new irrigation.