The industry standard base for the Midwest is 6 in.  However;  many companies just dig a 6-in hole,  When You Subtract out the 2” brick and ½” of leveling sand that go on top  many customers are left with less than three and a half inches of Base.  At Scott Flanagan landscape  it is always been our practice to dig a 12-in hole for patios leaving the customer with up to 10 in of compacted gravel.  in addition to that we don’t just use standard ca6 we start with 3 in stone  and large diesel compactors to integrate your base  into the undisturbed clay at the bottom of our excavation.  industry standard warranty is 2 years and covers only one freeze thaw cycle.  New Lenox Patio and Driveway Company gives the same 5 year warranty as scott flanagan landscape