I know IL, NY, CA and a few states have SE seperated from PE. How about the states (a majority I believe) taking care of this business - PE/Structural, PE/Geotechnical, PE/Civil..?
In Washington State the law reads significant structure and defines that by a number of criteria including 5 stories if it includes residential or 100 ft tall on any structure other than residential. The city of Seattle wrote their own Seattle Building Code (SBC) and require a structural license to do any structural calculations except for single story metal building.
Check with the building department where you will be building the structure. You may get a surprise if you don't check with the specific area.