This is one of the items we check during the inspection of new construction.  One of the energy code requirements is to have proper insulation in the attic space.  The required depth depends upon the standard you follow, which is either prescriptive or performance.  Regardless of the standard required, we find they don’t even install insulation to the minimum depth they specify.  You can find the required depth on the energy code data tag typically found in the panel box and on an installer’s data tag placed at the attic access.  The depth required in the photo was 13.25 inches for an R-38.  Note the significant variation from the marker to the tape.