I've had projects where the engineer specified 2" of topsoil in the tree lawn. I've had projects where 6" was specified.
Can a professional explain if there is a standard thickness of topsoil that should be used and some of the ins and outs?
How much thickness does a good root growth section need?
Can the topsoil be thinned up over certain material types and not others, dense material, clay versus sand, etc.